RE: [PATCH V1 2/4] nvmem: core: introduce "reverse-data" property to reverse buffer

[Joakim Zhang]

> -----Original Message-----
> From: Srinivas Kandagatla <srinivas.kandagatla@xxxxxxxxxx>
> Sent: 2021年8月11日 17:52
> To: Joakim Zhang <qiangqing.zhang@xxxxxxx>; robh+dt@xxxxxxxxxx;
> shawnguo@xxxxxxxxxx
> Cc: kernel@xxxxxxxxxxxxxx; dl-linux-imx <linux-imx@xxxxxxx>;
> devicetree@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH V1 2/4] nvmem: core: introduce "reverse-data" property
> to reverse buffer
> 
> 
> 
> On 10/08/2021 08:35, Joakim Zhang wrote:
> > This patch intends to introduce "reverse-data" property at nvmem
> > provider side to reverse buffer.
> >
> > For a case used from Ethernet driver, of_get_mac_address() may call
> > of_get_mac_addr_nvmem() to get MAC address from nvmem device. MAC
> > address programed in imx-ocopt is MSB first in lowest address, so need
> > reverse
> 
> Is all the data stored in imx-ocopt reverse byte order?

No, it depends on how users program these data.

> or someone decided to change the order for only mac-address?

No, will not change the order for mac-address, would be consistent.

> 
> > data then feedback to nvmem consumer. E.g. MAC address read from
> > imx-ocopt is 98:e2:06:9f:04:00, after reversed the data is
> > 00:04:9f:06:e2:98.
> >
> > Signed-off-by: Joakim Zhang <qiangqing.zhang@xxxxxxx>
> > ---
> >   drivers/nvmem/core.c           | 30
> ++++++++++++++++++++++++++++++
> >   include/linux/nvmem-provider.h |  2 ++
> >   2 files changed, 32 insertions(+)
> >
> > diff --git a/drivers/nvmem/core.c b/drivers/nvmem/core.c index
> > b3bc30a04ed7..ccc2c5801c8e 100644
> > --- a/drivers/nvmem/core.c
> > +++ b/drivers/nvmem/core.c
> > @@ -55,6 +55,7 @@ struct nvmem_cell {
> >   	struct device_node	*np;
> >   	struct nvmem_device	*nvmem;
> >   	struct list_head	node;
> > +	u32			flags;
> 
> This flag also needs to go in struct nvmem_cell_info too.

OK.

> >   };
> >
> >   static DEFINE_MUTEX(nvmem_mutex);
> > @@ -92,6 +93,26 @@ static int __nvmem_reg_write(struct nvmem_device
> *nvmem, unsigned int offset,
> >   	return -EINVAL;
> >   }
> >
> > +static int nvmem_buffer_reverse(void *bufaddr, int len) {
> > +	u8 *buf = (u8 *)bufaddr;
> > +	u8 *temp;
> > +	int i;
> > +
> > +	temp = kzalloc(len, GFP_KERNEL);
> > +	if (!temp)
> > +		return -ENOMEM;
> > +
> > +	memcpy(temp, buf, len);
> > +
> > +	for (i = 0; i < len; i++)
> > +		buf[i] = temp[len - i - 1];
> > +
> 
> You could possibly simplify this.
> 
> static void nvmem_buffer_reverse(u8 *buf, int len) {
> 	int i;
> 
> 	for (i = 0; i < len/2; i++)
> 		swap(buf[i], buf[len - i - 1]);
> }

Thanks.

> > +	kfree(temp);
> > +
> > +	return 0;
> > +}
> > +
> >   static int nvmem_access_with_keepouts(struct nvmem_device *nvmem,
> >   				      unsigned int offset, void *val,
> >   				      size_t bytes, int write)
> > @@ -705,6 +726,9 @@ static int nvmem_add_cells_from_of(struct
> nvmem_device *nvmem)
> >   		cell->bytes = be32_to_cpup(addr);
> >   		cell->name = kasprintf(GFP_KERNEL, "%pOFn", child);
> >
> > +		if (of_property_read_bool(child, "reverse-data"))
> > +			cell->flags |= NVMEM_FLAGS_REVERSE_DATA;
> > +
> >   		addr = of_get_property(child, "bits", &len);
> >   		if (addr && len == (2 * sizeof(u32))) {
> >   			cell->bit_offset = be32_to_cpup(addr++); @@ -1398,6
> +1422,12 @@
> > static int __nvmem_cell_read(struct nvmem_device *nvmem,
> >   	if (cell->bit_offset || cell->nbits)
> >   		nvmem_shift_read_buffer_in_place(cell, buf);
> >
> > +	if (cell->flags & NVMEM_FLAGS_REVERSE_DATA) {
> > +		rc = nvmem_buffer_reverse(buf, cell->bytes);
> > +		if (rc < 0)
> > +			return rc;
> > +	}
> > +
> >   	if (len)
> >   		*len = cell->bytes;
> >
> > diff --git a/include/linux/nvmem-provider.h
> > b/include/linux/nvmem-provider.h index 104505e9028f..364ac2a61b11
> > 100644
> > --- a/include/linux/nvmem-provider.h
> > +++ b/include/linux/nvmem-provider.h
> > @@ -31,6 +31,8 @@ enum nvmem_type {
> >   #define NVMEM_DEVID_NONE	(-1)
> >   #define NVMEM_DEVID_AUTO	(-2)
> >
> > +#define NVMEM_FLAGS_REVERSE_DATA	BIT(0)
> 
> Maybe NVMEM_FLAGS_REVERSE_BYTE_ORDER and some kerneldoc would
> help new users.

Yes, will rename it, could you please point me where nvmem kerneldoc there to add new info?

Best Regards,
Joakim Zhang
> --srini
> > +
> >   /**
> >    * struct nvmem_keepout - NVMEM register keepout range.
> >    *
> >