Re: [PATCH v3 05/17] mtd: spinand: Define ctrl_ops for non-page read/write op templates

[Apurva Nandan]

Hi Boris,

On 03/01/22 15:31, Boris Brezillon wrote:
> On Sat, 1 Jan 2022 13:12:38 +0530
> Apurva Nandan <a-nandan@xxxxxx> wrote:
>
> > 'ctrl_ops' are op templates for non-page read/write operations,
> > which are: reset, get_feature, set_feature, write_enable, block_erase,
> > page_read and program_execute ops. The 'ctrl_ops' struct contains in it
> > op templates for each of this op, as well as enum spinand_protocol
> > denoting protocol of all these ops.
> >
> > We require these new op templates because of deviation in standard
> > SPINAND ops by manufacturers and also due to changes when there is a
> > change in SPI protocol/mode. This prevents the core from live-patching
> > and vendor-specific adjustments in ops.
> >
> > Define 'ctrl_ops', add macros to initialize it and add it in
> > spinand_device.
> >
> > Signed-off-by: Apurva Nandan <a-nandan@xxxxxx>
> > ---
> >   include/linux/mtd/spinand.h | 33 +++++++++++++++++++++++++++++++++
> >   1 file changed, 33 insertions(+)
> >
> > diff --git a/include/linux/mtd/spinand.h b/include/linux/mtd/spinand.h
> > index 439d8ce40e1d..e5df6220ec1e 100644
> > --- a/include/linux/mtd/spinand.h
> > +++ b/include/linux/mtd/spinand.h
> > @@ -356,6 +356,35 @@ struct spinand_op_variants {
> >   			sizeof(struct spi_mem_op),			\
> >   	}
> >   
> > +struct spinand_ctrl_ops {
> > +	const struct {
> > +		struct spi_mem_op reset;
> > +		struct spi_mem_op get_feature;
> > +		struct spi_mem_op set_feature;
> > +		struct spi_mem_op write_enable;
> > +		struct spi_mem_op block_erase;
> > +		struct spi_mem_op page_read;
> > +		struct spi_mem_op program_execute;
> > +	} ops;
> > +	const enum spinand_protocol protocol;
> Do you really need that protocol field?
>
> > +};
> > +
> > +#define SPINAND_CTRL_OPS(__protocol, __reset, __get_feature, __set_feature,	\
> > +			 __write_enable, __block_erase, __page_read,		\
> > +			 __program_execute)					\
> > +	{									\
> > +		.ops = {							\
> > +			.reset = __reset,					\
> > +			.get_feature = __get_feature,				\
> > +			.set_feature = __set_feature,				\
> > +			.write_enable = __write_enable,				\
> > +			.block_erase = __block_erase,				\
> > +			.page_read = __page_read,				\
> > +			.program_execute = __program_execute,			\
> > +		},								\
> > +		.protocol = __protocol,						\
> > +	}
> > +
> >   /**
> >    * spinand_ecc_info - description of the on-die ECC implemented by a SPI NAND
> >    *		      chip
> > @@ -468,6 +497,8 @@ struct spinand_dirmap {
> >    * @data_ops.read_cache: read cache op template
> >    * @data_ops.write_cache: write cache op template
> >    * @data_ops.update_cache: update cache op template
> > + * @ctrl_ops: various SPI mem op templates for handling the flash device, i.e.
> > + *	      non page-read/write ops.
> >    * @select_target: select a specific target/die. Usually called before sending
> >    *		   a command addressing a page or an eraseblock embedded in
> >    *		   this die. Only required if your chip exposes several dies
> > @@ -498,6 +529,8 @@ struct spinand_device {
> >   		const struct spi_mem_op *update_cache;
> >   	} data_ops;
> >   
> > +	const struct spinand_ctrl_ops *ctrl_ops;
> > +
> Okay, I had something slightly different in mind. First, I'd put all
> templates in a struct:
>
> struct spinand_op_templates {
> 	const struct spi_mem_op *read_cache;
> 	const struct spi_mem_op *write_cache;
> 	const struct spi_mem_op *update_cache;
> 	const struct spi_mem_op *reset;
> 	const struct spi_mem_op *get_feature;
> 	const struct spi_mem_op *set_feature;
> 	const struct spi_mem_op *write_enable;
> 	const struct spi_mem_op *block_erase;
> 	const struct spi_mem_op *page_load;
> 	const struct spi_mem_op *program_execute;
> };
>
> Then, at the spinand level, I'd define an array of templates:
>
> enum spinand_protocol {
> 	SPINAND_1S_1S_1S,
> 	SPINAND_2S_2S_2S,
> 	SPINAND_4S_4S_4S,
> 	SPINAND_8S_8S_8S,
> 	SPINAND_8D_8D_8D,
> 	SPINAND_NUM_PROTOCOLS,
> };
>
> struct spinand_device {
> 	...
> 	enum spinand_protocol protocol;
> 	const struct spinand_op_templates *op_templates[SPINAND_NUM_PROTOCOLS];
> 	...
> };
>
> This way, you can easily pick the right set of operations based
> on the protocol/mode you're in:
>
> #define spinand_get_op_template(spinand, opname) \
> 	((spinand)->op_templates[(spinand)->protocol]->opname)
>
> static int spinand_read_reg_op(struct spinand_device *spinand, u8 reg, u8 *val)
> {
> 	struct spi_mem_op op = *spinand_get_op_template(spinand, get_feature);
> 	int ret;
>
> 	...
> }

I find a couple of issues with this  method,

1. read_cache, write_cache, update_cache op templates don't fit well 
with the other non-data ops, as
these data ops are used to create a dirmap, and that can be done only 
once at probe time. Hence, there
is a different mechanism of selecting of data ops and non-data ops. 
Hence, this division in the op templates
struct as data_ops and ctrl_ops is required. Currently, the core only 
supports using a single protocol for
data ops, chosen at the time of probing.

2. If we use this single op_templates struct, I can't think of any good 
way to initialize these in the
manufacturers driver (winbond.c), refer to 17th patch in this series. 
Could you please suggest a macro
implementation also for winbond.c with the suggested op_templates struct.

Thanks,
Apurva Nandan