RE: [PATCH V8 1/7] spi: Add stacked and parallel memories support in SPI core

[Mahapatra, Amit Kumar]

Hello Pratyush,

> -----Original Message-----
> From: Pratyush Yadav <pratyush@xxxxxxxxxx>
> Sent: Tuesday, May 30, 2023 9:56 PM
> To: Mahapatra, Amit Kumar <amit.kumar-mahapatra@xxxxxxx>
> Cc: broonie@xxxxxxxxxx; tudor.ambarus@xxxxxxxxxx; pratyush@xxxxxxxxxx;
> miquel.raynal@xxxxxxxxxxx; richard@xxxxxx; vigneshr@xxxxxx;
> michael@xxxxxxxx; sbinding@xxxxxxxxxxxxxxxxxxxxx; git (AMD-Xilinx)
> <git@xxxxxxx>; linux-spi@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> linux-mtd@xxxxxxxxxxxxxxxxxxx; nicolas.ferre@xxxxxxxxxxxxx;
> alexandre.belloni@xxxxxxxxxxx; claudiu.beznea@xxxxxxxxxxxxx; Simek,
> Michal <michal.simek@xxxxxxx>; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx;
> amitrkcian2002@xxxxxxxxx
> Subject: Re: [PATCH V8 1/7] spi: Add stacked and parallel memories support in
> SPI core
> 
> Hi Amit,
> 
> I did not get a chance to look at all the old comments in the previous versions.
> So apologies in advance if I comment something that has already been
> mentioned before.
> 
> On Thu, May 11 2023, Amit Kumar Mahapatra wrote:
> 
> > For supporting multiple CS the SPI device need to be aware of all the
> > CS values. So, the "chip_select" member in the spi_device structure is
> > now an array that holds all the CS values.
> >
> > spi_device structure now has a "cs_index_mask" member. This acts as an
> > index to the chip_select array. If nth bit of spi->cs_index_mask is
> > set then the driver would assert spi->chip_select[n].
> >
> > In parallel mode all the chip selects are asserted/de-asserted
> > simultaneously and each byte of data is stored in both devices, the
> > even bits in one, the odd bits in the other. The split is
> > automatically handled by the GQSPI controller. The GQSPI controller
> > supports a maximum of two flashes connected in parallel mode. A
> > SPI_CONTROLLER_MULTI_CS flag bit is added in the spi controntroller
> > flags, through ctlr->flags the spi core
> 
> Typo: s/controntroller/controller/

I will fix it.
> 
> > will make sure that the controller is capable of handling multiple
> > chip selects at once.
> >
> > For supporting multiple CS via GPIO the cs_gpiod member of the
> > spi_device structure is now an array that holds the gpio descriptor
> > for each chipselect.
> 
> General comment: For large changes, it is useful to describe a high-level
> overview of your new design so reviewers and future readers can get a
> mental model of what is going on. I did not see anything of that sort in this
> series.

I will add a high-level overview of multi-cs and stacked connection mode.
> 
> >
> > Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@xxxxxxx>
> > ---
> > CS GPIO is not tested on our hardware but it has been tested by
> > @Stefan
> > https://lore.kernel.org/all/3f148a0c-8885-0425-28f4-2a53937a388f@opens
> > ource.cirrus.com/ Stefan, could you please provide your Tested-by tag
> > for this patch
> > ---
> >  drivers/spi/spi.c       | 231 ++++++++++++++++++++++++++++------------
> >  include/linux/spi/spi.h |  32 ++++--
> >  2 files changed, 189 insertions(+), 74 deletions(-)
> >
> > diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
> >
> > index 9291b2a0e887..a793e56f6a21 100644
> > --- a/drivers/spi/spi.c
> > +++ b/drivers/spi/spi.c
> > @@ -612,10 +612,24 @@ static int spi_dev_check(struct device *dev,
> > void *data)  {
> >  	struct spi_device *spi = to_spi_device(dev);
> >  	struct spi_device *new_spi = data;
> > +	int idx, nw_idx;
> >
> > -	if (spi->controller == new_spi->controller &&
> > -	    spi_get_chipselect(spi, 0) == spi_get_chipselect(new_spi, 0))
> > -		return -EBUSY;
> > +	if (spi->controller == new_spi->controller) {
> > +		for (idx = 0; idx < SPI_CS_CNT_MAX; idx++) {
> > +			for (nw_idx = 0; nw_idx < SPI_CS_CNT_MAX;
> nw_idx++) {
> > +				if ((idx != 0 && !spi_get_chipselect(spi, idx))
> ||
> > +				    (nw_idx != 0 && !spi_get_chipselect(spi,
> nw_idx))) {
> 
> Hmm, from what I can understand, spi->chipselect[i] gives the corresponding
> physical CS for logical CS i. So for example, if both old and new devices map
> logical CS 1 to physical CS 0, this would not detect the conflict.

Yes that's correct. 
> 
> What exactly are you trying to do here?

Initially by default all the spi->chip_select[i] are initialized to 0. 
If a single slave device is connected to the physical CS 1 of the 
controller, then the spi->chip_select[0] will hold 1 and 
spi->chip_select[0] will hold 0 (the default value).  
So, both the old and new devices spi->chip_select[1] holds the default 
value 0 and spi_dev_check() will error out by saying that 
physical CS 0 (i.e., spi->chip_select[1]) is already in use, which is not actually true as 
spi->chip_select[1] doesn't contain any valid CS number. 
To avoid this false trigger, we have this check in which we assume that 
except logical CS 0(i.e., spi->chip_select[0]) if any other logical CS 
holds 0 then it's not a valid physical CS but rather the default value.
This logic though has the downside as mentioned in your previous comment.

As an alternate solution we can initialize all the unused 
spi->chip_select[i] to FF, in that case we can remove this check and any 
combination of logical CS to physical CS can be covered. But if some 
controller has FF (which is unlikely but still a possibility) as a valid 
physical CS then this logic might not work.

please provide your thoughts on the same.
> 
> > +					continue;
> > +				} else if (spi_get_chipselect(spi, idx) ==
> > +				    spi_get_chipselect(new_spi, nw_idx)) {
> > +					dev_err(dev,
> > +						"chipselect %d already in
> use\n",
> > +						spi_get_chipselect(new_spi,
> nw_idx));
> > +					return -EBUSY;
> > +				}
> > +			}
> > +		}
> > +	}
> >  	return 0;
> >  }
> >
> > @@ -629,7 +643,7 @@ static int __spi_add_device(struct spi_device
> > *spi)  {
> >  	struct spi_controller *ctlr = spi->controller;
> >  	struct device *dev = ctlr->dev.parent;
> > -	int status;
> > +	int status, idx;
> >
> >  	/*
> >  	 * We need to make sure there's no other device with this @@ -638,8
> > +652,6 @@ static int __spi_add_device(struct spi_device *spi)
> >  	 */
> >  	status = bus_for_each_dev(&spi_bus_type, NULL, spi, spi_dev_check);
> >  	if (status) {
> > -		dev_err(dev, "chipselect %d already in use\n",
> > -				spi_get_chipselect(spi, 0));
> 
> Nitpick: No need for the braces around if anymore.

Will fix it in next version.
> 
> >  		return status;
> >  	}
> >
> > @@ -649,8 +661,13 @@ static int __spi_add_device(struct spi_device *spi)
> >  		return -ENODEV;
> >  	}
> >
> > -	if (ctlr->cs_gpiods)
> > -		spi_set_csgpiod(spi, 0, ctlr->cs_gpiods[spi_get_chipselect(spi,
> 0)]);
> > +	if (ctlr->cs_gpiods) {
> > +		for (idx = 0; idx < SPI_CS_CNT_MAX; idx++) {
> > +			if (!(idx != 0 && !spi_get_chipselect(spi, idx)))
> 
> Again, I don't get why you do this. This would simply fail for any device that
> maps logical CS 1 to physical CS 0.

I have explained the reason above.
> 
> > +				spi_set_csgpiod(spi, idx,
> > +						ctlr-
> >cs_gpiods[spi_get_chipselect(spi, idx)]);
> > +		}
> > +	}
> >
> >  	/*
> >  	 * Drivers may modify this initial i/o setup, but will @@ -690,13
> > +707,15 @@ int spi_add_device(struct spi_device *spi)  {
> >  	struct spi_controller *ctlr = spi->controller;
> >  	struct device *dev = ctlr->dev.parent;
> > -	int status;
> > +	int status, idx;
> >
> > -	/* Chipselects are numbered 0..max; validate. */
> > -	if (spi_get_chipselect(spi, 0) >= ctlr->num_chipselect) {
> > -		dev_err(dev, "cs%d >= max %d\n", spi_get_chipselect(spi, 0),
> > -			ctlr->num_chipselect);
> > -		return -EINVAL;
> > +	for (idx = 0; idx < SPI_CS_CNT_MAX; idx++) {
> > +		/* Chipselects are numbered 0..max; validate. */
> > +		if (spi_get_chipselect(spi, idx) >= ctlr->num_chipselect) {
> > +			dev_err(dev, "cs%d >= max %d\n",
> spi_get_chipselect(spi, idx),
> > +				ctlr->num_chipselect);
> > +			return -EINVAL;
> > +		}
> 
> Since this function is doing a bunch of sanity checks, I think you should also
> make sure multiple logical CS don't map to the same physical CS. For
> example, make sure that spi->chip_select[0] !=
> spi->chip_select[1] and so on.

I will add the check.
> 
> >  	}
> >
> >  	/* Set the bus ID string */
> > @@ -713,12 +732,15 @@ static int spi_add_device_locked(struct
> > spi_device *spi)  {
> >  	struct spi_controller *ctlr = spi->controller;
> >  	struct device *dev = ctlr->dev.parent;
> > +	int idx;
> >
> > -	/* Chipselects are numbered 0..max; validate. */
> > -	if (spi_get_chipselect(spi, 0) >= ctlr->num_chipselect) {
> > -		dev_err(dev, "cs%d >= max %d\n", spi_get_chipselect(spi, 0),
> > -			ctlr->num_chipselect);
> > -		return -EINVAL;
> > +	for (idx = 0; idx < SPI_CS_CNT_MAX; idx++) {
> > +		/* Chipselects are numbered 0..max; validate. */
> > +		if (spi_get_chipselect(spi, idx) >= ctlr->num_chipselect) {
> > +			dev_err(dev, "cs%d >= max %d\n",
> spi_get_chipselect(spi, idx),
> > +				ctlr->num_chipselect);
> > +			return -EINVAL;
> > +		}
> 
> As adding a new device gets more complex, we should stop duplicating code
> between here and spi_add_device(). So you should either move this code to
> another function and call it from both places or add a new parameter called
> "locked" and merge spi_add_device() and spi_add_device_locked(). I do not
> have string preferences for either, but I do like the latter a bit more.

Agreed, will try to merge the functions into one.
> 
> >  	}
> >
> >  	/* Set the bus ID string */
> > @@ -966,58 +988,122 @@ static void spi_res_release(struct
> > spi_controller *ctlr, struct spi_message *mes  static void
> > spi_set_cs(struct spi_device *spi, bool enable, bool force)  {
> >  	bool activate = enable;
> > +	u32 cs_num = 0;
> > +	int idx;
> >
> >  	/*
> > -	 * Avoid calling into the driver (or doing delays) if the chip select
> > -	 * isn't actually changing from the last time this was called.
> > +	 * In parallel mode all the chip selects are asserted/de-asserted
> > +	 * at once
> >  	 */
> > -	if (!force && ((enable && spi->controller->last_cs ==
> spi_get_chipselect(spi, 0)) ||
> > -		       (!enable && spi->controller->last_cs !=
> spi_get_chipselect(spi, 0))) &&
> > -	    (spi->controller->last_cs_mode_high == (spi->mode &
> SPI_CS_HIGH)))
> > -		return;
> > -
> > -	trace_spi_set_cs(spi, activate);
> > +	if ((spi->cs_index_mask & SPI_PARALLEL_CS_MASK) ==
> > +SPI_PARALLEL_CS_MASK) {
> 
> This check only works if you support a maximum of 2 CS in parallel. If you
> support up to, say, 4 then a chip which sets only CS 0 and 2 would not fall
> under this check.


Yes correct, this support is not added.
> 
> I think your code in general should treat SPI_CS_CNT_MAX as an arbitrary
> value and should be able to handle changing it to any reasonable value.

I will rework on the logic.
> 
> > +		spi->controller->last_cs_mode_high = spi->mode &
> SPI_CS_HIGH;
> > +
> > +		if ((spi_get_csgpiod(spi, 0) || !spi->controller->set_cs_timing)
> && !activate)
> > +			spi_delay_exec(&spi->cs_hold, NULL);
> > +
> > +		if (spi->mode & SPI_CS_HIGH)
> > +			enable = !enable;
> > +
> > +		if (spi_get_csgpiod(spi, 0) && spi_get_csgpiod(spi, 1)) {
> > +			if (!(spi->mode & SPI_NO_CS)) {
> > +				/*
> > +				 * Historically ACPI has no means of the GPIO
> polarity and
> > +				 * thus the SPISerialBus() resource defines it
> on the per-chip
> > +				 * basis. In order to avoid a chain of
> negations, the GPIO
> > +				 * polarity is considered being Active High.
> Even for the cases
> > +				 * when _DSD() is involved (in the updated
> versions of ACPI)
> > +				 * the GPIO CS polarity must be defined Active
> High to avoid
> > +				 * ambiguity. That's why we use enable, that
> takes SPI_CS_HIGH
> > +				 * into account.
> > +				 */
> > +				if (has_acpi_companion(&spi->dev)) {
> > +					for (idx = 0; idx < SPI_CS_CNT_MAX;
> idx++)
> > +
> 	gpiod_set_value_cansleep(spi_get_csgpiod(spi, idx),
> > +
> !enable);
> > +				} else {
> > +					for (idx = 0; idx < SPI_CS_CNT_MAX;
> idx++)
> > +						/* Polarity handled by GPIO
> library */
> > +
> 	gpiod_set_value_cansleep(spi_get_csgpiod(spi, idx),
> > +
> activate);
> > +				}
> > +			}
> > +			/* Some SPI masters need both GPIO CS &
> slave_select */
> > +			if ((spi->controller->flags & SPI_MASTER_GPIO_SS)
> &&
> > +			    spi->controller->set_cs)
> > +				spi->controller->set_cs(spi, !enable);
> > +		} else if (spi->controller->set_cs) {
> > +			spi->controller->set_cs(spi, !enable);
> > +		}
> >
> > -	spi->controller->last_cs = enable ? spi_get_chipselect(spi, 0) : -1;
> > -	spi->controller->last_cs_mode_high = spi->mode & SPI_CS_HIGH;
> > +		if (spi_get_csgpiod(spi, 0) || spi_get_csgpiod(spi, 1) ||
> > +		    !spi->controller->set_cs_timing) {
> > +			if (activate)
> > +				spi_delay_exec(&spi->cs_setup, NULL);
> > +			else
> > +				spi_delay_exec(&spi->cs_inactive, NULL);
> > +		}
> > +	} else {
> >
> > -	if ((spi_get_csgpiod(spi, 0) || !spi->controller->set_cs_timing) &&
> !activate)
> > -		spi_delay_exec(&spi->cs_hold, NULL);
> > +		if (spi->cs_index_mask)
> > +			cs_num = ffs(spi->cs_index_mask) - 1;
> >
> > -	if (spi->mode & SPI_CS_HIGH)
> > -		enable = !enable;
> > +		/*
> > +		 * Avoid calling into the driver (or doing delays) if the chip
> select
> > +		 * isn't actually changing from the last time this was called.
> > +		 */
> > +		if (!force && ((enable && spi->controller->last_cs ==
> > +				spi_get_chipselect(spi, cs_num)) ||
> > +				(!enable && spi->controller->last_cs !=
> > +				 spi_get_chipselect(spi, cs_num))) &&
> > +		    (spi->controller->last_cs_mode_high ==
> > +		     (spi->mode & SPI_CS_HIGH)))
> > +			return;
> > +
> > +		trace_spi_set_cs(spi, activate);
> > +
> > +		spi->controller->last_cs = enable ? spi_get_chipselect(spi,
> cs_num) : -1;
> > +		spi->controller->last_cs_mode_high = spi->mode &
> SPI_CS_HIGH;
> > +
> > +		if ((spi_get_csgpiod(spi, cs_num) || !spi->controller-
> >set_cs_timing) && !activate)
> > +			spi_delay_exec(&spi->cs_hold, NULL);
> > +
> > +		if (spi->mode & SPI_CS_HIGH)
> > +			enable = !enable;
> > +
> > +		if (spi_get_csgpiod(spi, cs_num)) {
> > +			if (!(spi->mode & SPI_NO_CS)) {
> > +				/*
> > +				 * Historically ACPI has no means of the GPIO
> polarity and
> > +				 * thus the SPISerialBus() resource defines it
> on the per-chip
> > +				 * basis. In order to avoid a chain of
> negations, the GPIO
> > +				 * polarity is considered being Active High.
> Even for the cases
> > +				 * when _DSD() is involved (in the updated
> versions of ACPI)
> > +				 * the GPIO CS polarity must be defined Active
> High to avoid
> > +				 * ambiguity. That's why we use enable, that
> takes SPI_CS_HIGH
> > +				 * into account.
> > +				 */
> > +				if (has_acpi_companion(&spi->dev))
> > +
> 	gpiod_set_value_cansleep(spi_get_csgpiod(spi, cs_num),
> > +								 !enable);
> > +				else
> > +					/* Polarity handled by GPIO library */
> > +
> 	gpiod_set_value_cansleep(spi_get_csgpiod(spi, cs_num),
> > +								 activate);
> > +			}
> > +			/* Some SPI masters need both GPIO CS &
> slave_select */
> > +			if ((spi->controller->flags & SPI_MASTER_GPIO_SS)
> &&
> > +			    spi->controller->set_cs)
> > +				spi->controller->set_cs(spi, !enable);
> > +		} else if (spi->controller->set_cs) {
> > +			spi->controller->set_cs(spi, !enable);
> > +		}
> >
> > -	if (spi_get_csgpiod(spi, 0)) {
> > -		if (!(spi->mode & SPI_NO_CS)) {
> > -			/*
> > -			 * Historically ACPI has no means of the GPIO polarity
> and
> > -			 * thus the SPISerialBus() resource defines it on the
> per-chip
> > -			 * basis. In order to avoid a chain of negations, the
> GPIO
> > -			 * polarity is considered being Active High. Even for
> the cases
> > -			 * when _DSD() is involved (in the updated versions of
> ACPI)
> > -			 * the GPIO CS polarity must be defined Active High to
> avoid
> > -			 * ambiguity. That's why we use enable, that takes
> SPI_CS_HIGH
> > -			 * into account.
> > -			 */
> > -			if (has_acpi_companion(&spi->dev))
> > -
> 	gpiod_set_value_cansleep(spi_get_csgpiod(spi, 0), !enable);
> > +		if (spi_get_csgpiod(spi, cs_num) || !spi->controller-
> >set_cs_timing) {
> > +			if (activate)
> > +				spi_delay_exec(&spi->cs_setup, NULL);
> >  			else
> > -				/* Polarity handled by GPIO library */
> > -
> 	gpiod_set_value_cansleep(spi_get_csgpiod(spi, 0), activate);
> > +				spi_delay_exec(&spi->cs_inactive, NULL);
> >  		}
> > -		/* Some SPI masters need both GPIO CS & slave_select */
> > -		if ((spi->controller->flags & SPI_MASTER_GPIO_SS) &&
> > -		    spi->controller->set_cs)
> > -			spi->controller->set_cs(spi, !enable);
> > -	} else if (spi->controller->set_cs) {
> > -		spi->controller->set_cs(spi, !enable);
> > -	}
> > -
> > -	if (spi_get_csgpiod(spi, 0) || !spi->controller->set_cs_timing) {
> > -		if (activate)
> > -			spi_delay_exec(&spi->cs_setup, NULL);
> > -		else
> > -			spi_delay_exec(&spi->cs_inactive, NULL);
> 
> I did not read this blob of code in detail yet. A couple of general comments
> though. You seem to be special-casing the multi-CS path. I do not think that is
> a good idea in general. Can you refactor it in such a way that the same bit of
> code handles an arbitrary number of chip selects being asserted at the same
> time?

Ok, I will rework to make a common code for asserting an arbitrary number of chip selects.
> 
> >  	}
> >  }
> >
> > @@ -2246,8 +2332,8 @@ static void of_spi_parse_dt_cs_delay(struct
> > device_node *nc,  static int of_spi_parse_dt(struct spi_controller *ctlr, struct
> spi_device *spi,
> >  			   struct device_node *nc)
> >  {
> > -	u32 value;
> > -	int rc;
> > +	u32 value, cs[SPI_CS_CNT_MAX] = {0};
> > +	int rc, idx;
> >
> >  	/* Mode (clock phase/polarity/etc.) */
> >  	if (of_property_read_bool(nc, "spi-cpha")) @@ -2320,13 +2406,21
> @@
> > static int of_spi_parse_dt(struct spi_controller *ctlr, struct spi_device *spi,
> >  	}
> >
> >  	/* Device address */
> > -	rc = of_property_read_u32(nc, "reg", &value);
> > -	if (rc) {
> > +	rc = of_property_read_variable_u32_array(nc, "reg", &cs[0], 1,
> > +						 SPI_CS_CNT_MAX);
> > +	if (rc < 0 || rc > ctlr->num_chipselect) {
> >  		dev_err(&ctlr->dev, "%pOF has no valid 'reg' property
> (%d)\n",
> >  			nc, rc);
> 
> This error message is not very helpful for the rc > ctlr->num_chipselect case. I
> think you should make them separate checks and error messages.

Ok,  will separate the error checks.
> 
> >  		return rc;
> > +	} else if ((of_property_read_bool(nc, "parallel-memories")) &&
> 
> Nitpick: Why make it an else-if chain? Independent if statements would be
> better since these are not directly related.

Agreed.
> 
> > +		   (!(ctlr->flags & SPI_CONTROLLER_MULTI_CS))) {
> > +		dev_err(&ctlr->dev, "SPI controller doesn't support multi
> CS\n");
> > +		return -EINVAL;
> >  	}
> 
> You should also make sure that no cs[idx] is greater than

Agreed, I will add the check. 
> ctlr->num_chipselect. Perhaps also check for multple cs[idx] pointing to
> ctlr->the
> same physical CS? It might be better to check that in spi_add_device() though.
> Not sure...
> 
> > -	spi_set_chipselect(spi, 0, value);
> > +	for (idx = 0; idx < rc; idx++)
> > +		spi_set_chipselect(spi, idx, cs[idx]);
> > +	/* By default set the spi->cs_index_mask as 1 */
> 
> Nitpick: We can infer this fact quite easily by reading the code. The comment
> should instead explain _why_ it is doing so.

I will add the explanation in comment.
> 
> > +	spi->cs_index_mask = 0x01;
> >
> >  	/* Device speed */
> >  	if (!of_property_read_u32(nc, "spi-max-frequency", &value)) @@
> > -3905,7 +3999,8 @@ static int __spi_validate(struct spi_device *spi, struct
> spi_message *message)
> >  	 * cs_change is set for each transfer.
> >  	 */
> >  	if ((spi->mode & SPI_CS_WORD) && (!(ctlr->mode_bits &
> SPI_CS_WORD) ||
> > -					  spi_get_csgpiod(spi, 0))) {
> > +					  spi_get_csgpiod(spi, 0) ||
> > +					  spi_get_csgpiod(spi, 1))) {
> 
> Again, you hard-code this to only ever supporting 2 CS in parallel.
> Please make it generic.

Ok, will make it generic. 
> 
> >  		size_t maxsize;
> >  		int ret;
> >
> > diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h index
> > cfe42f8cd7a4..d0f9a9a8b6d8 100644
> > --- a/include/linux/spi/spi.h
> > +++ b/include/linux/spi/spi.h
> > @@ -19,6 +19,11 @@
> >  #include <linux/acpi.h>
> >  #include <linux/u64_stats_sync.h>
> >
> > +/* Max no. of CS supported per spi device */ #define SPI_CS_CNT_MAX 2
> 
> This is fine, but...
> 
> > +
> > +/* chip select mask */
> > +#define SPI_PARALLEL_CS_MASK	(BIT(0) | BIT(1))
> 
> ... as I mentioned above, the way you write this patch you makes it difficult to
> change the limit in the future. Please refactor it so that if you just change
> SPI_CS_CNT_MAX to any arbitrary value, the core is able to handle it.
> 
> I also think calling it "parallel" can be a bit confusing. Perhaps use "Multi CS"
> everywhere?

I named it parallel to align it with the DT property "parallel-memories"?  
> 
> >  struct dma_chan;
> >  struct software_node;
> >  struct ptp_system_timestamp;
> > @@ -166,6 +171,7 @@ extern void
> spi_transfer_cs_change_delay_exec(struct spi_message *msg,
> >   *	deasserted. If @cs_change_delay is used from @spi_transfer, then
> the
> >   *	two delays will be added up.
> >   * @pcpu_statistics: statistics for the spi_device
> > + * @cs_index_mask: Bit mask of the active chipselect(s) in the
> > + chipselect array
> >   *
> >   * A @spi_device is used to interchange data between an SPI slave
> >   * (usually a discrete chip) and CPU memory.
> > @@ -181,7 +187,7 @@ struct spi_device {
> >  	struct spi_controller	*controller;
> >  	struct spi_controller	*master;	/* Compatibility layer */
> >  	u32			max_speed_hz;
> > -	u8			chip_select;
> > +	u8			chip_select[SPI_CS_CNT_MAX];
> 
> Should also update documentation for chip_select.

Will update it.

Regards,
Amit
> 
> >  	u8			bits_per_word;
> >  	bool			rt;
> >  #define SPI_NO_TX		BIT(31)		/* No transmit wire */
> > @@ -212,7 +218,7 @@ struct spi_device {
> >  	void			*controller_data;
> >  	char			modalias[SPI_NAME_SIZE];
> >  	const char		*driver_override;
> > -	struct gpio_desc	*cs_gpiod;	/* Chip select gpio desc */
> > +	struct gpio_desc	*cs_gpiod[SPI_CS_CNT_MAX];	/* Chip select
> gpio desc */
> >  	struct spi_delay	word_delay; /* Inter-word delay */
> >  	/* CS delays */
> >  	struct spi_delay	cs_setup;
> > @@ -222,6 +228,13 @@ struct spi_device {
> >  	/* The statistics */
> >  	struct spi_statistics __percpu	*pcpu_statistics;
> >
> > +	/* Bit mask of the chipselect(s) that the driver need to use from
> > +	 * the chipselect array.When the controller is capable to handle
> > +	 * multiple chip selects & memories are connected in parallel
> > +	 * then more than one bit need to be set in cs_index_mask.
> > +	 */
> > +	u32			cs_index_mask : SPI_CS_CNT_MAX;
> > +
> >  	/*
> >  	 * likely need more hooks for more protocol options affecting how
> >  	 * the controller talks to each chip, like:
> > @@ -278,22 +291,22 @@ static inline void *spi_get_drvdata(const struct
> > spi_device *spi)
> >
> >  static inline u8 spi_get_chipselect(const struct spi_device *spi, u8
> > idx)  {
> > -	return spi->chip_select;
> > +	return spi->chip_select[idx];
> >  }
> >
> >  static inline void spi_set_chipselect(struct spi_device *spi, u8 idx,
> > u8 chipselect)  {
> > -	spi->chip_select = chipselect;
> > +	spi->chip_select[idx] = chipselect;
> >  }
> >
> >  static inline struct gpio_desc *spi_get_csgpiod(const struct
> > spi_device *spi, u8 idx)  {
> > -	return spi->cs_gpiod;
> > +	return spi->cs_gpiod[idx];
> >  }
> >
> >  static inline void spi_set_csgpiod(struct spi_device *spi, u8 idx,
> > struct gpio_desc *csgpiod)  {
> > -	spi->cs_gpiod = csgpiod;
> > +	spi->cs_gpiod[idx] = csgpiod;
> >  }
> >
> >  /**
> > @@ -398,6 +411,8 @@ extern struct spi_device
> *spi_new_ancillary_device(struct spi_device *spi, u8 ch
> >   * @bus_lock_spinlock: spinlock for SPI bus locking
> >   * @bus_lock_mutex: mutex for exclusion of multiple callers
> >   * @bus_lock_flag: indicates that the SPI bus is locked for exclusive
> > use
> > + * @multi_cs_cap: indicates that the SPI Controller can assert/de-assert
> > + *	more than one chip select at once.
> >   * @setup: updates the device mode and clocking records used by a
> >   *	device's SPI controller; protocol code may call this.  This
> >   *	must fail if an unrecognized or unsupported mode is requested.
> > @@ -564,6 +579,11 @@ struct spi_controller {
> >  #define SPI_CONTROLLER_MUST_TX		BIT(4)	/* Requires tx */
> >
> >  #define SPI_MASTER_GPIO_SS		BIT(5)	/* GPIO CS must
> select slave */
> > +	/*
> > +	 * The spi-controller has multi chip select capability and can
> > +	 * assert/de-assert more than one chip select at once.
> > +	 */
> > +#define SPI_CONTROLLER_MULTI_CS		BIT(6)
> >
> >  	/* Flag indicating if the allocation of this struct is devres-managed */
> >  	bool			devm_allocated;
> 
> I only took a high level overview of this patch and I think it needs some
> reworking. I will take another look later when it gets in better shape. I am
> especially worried about interactions with SPI MEM (not sure if there need to
> be any, but still I should take a look) and ACPI support. But I think you have
> your work cut out for you for the next version :-)
> 
> I also want to look at the SPI NOR parts, let's see if I can find some more time
> this week.
> 
> --
> Regards,
> Pratyush Yadav