Re: [PATCH] m25p80: Add the is25wp256 SFPD table

[Guenter Roeck <linux@roeck-us.net>]

On Mon, Jan 02, 2023 at 04:43:49PM +0100, Michael Walle wrote:
> Am 2023-01-02 14:53, schrieb Cédric Le Goater:
> > On 12/27/22 07:31, Tudor Ambarus wrote:
> > > 
> > > 
> > > On 25.12.2022 14:18, Ben Dooks wrote:
> > > > On Wed, Dec 21, 2022 at 06:36:02PM +0100, Cédric Le Goater wrote:
> > > > > On 12/21/22 13:22, Guenter Roeck wrote:
> > > > > > Generated from hardware using the following command and
> > > > > > then padding
> > > > > > with 0xff to fill out a power-of-2:
> > > > > >     xxd -p /sys/bus/spi/devices/spi0.0/spi-nor/sfdp
> > > > > > 
> > > > > > Cc: Michael Walle <michael@walle.cc>
> > > > > > Cc: Tudor Ambarus <tudor.ambarus@linaro.org>
> > > > > > Signed-off-by: Guenter Roeck <linux@roeck-us.net>
> > > > > 
> > > > > Reviewed-by: Cédric Le Goater <clg@kaod.org>
> > > > 
> > > > If SFDP is a standard, couldn't we have an function to generate
> > > > it from
> > > > the flash parameters?
> > > > 
> > > 
> > > No, it's not practical as you have to specify all the flash parameters
> > > at flash declaration.
> > 
> > Indeed and the definition of flash models in QEMU is far to cover all
> > the SFDP
> > features. The known_devices array of m25p80 would be huge ! However, we
> > could
> > generate some of the SFDP tables if no raw data is provided. It could be
> > useful
> > for testing drivers.
> 
> I don't think adding (incomplete) SFDP tables makes sense for any real
> devices. E.g. sometimes our linux driver will look at specific bits in
> SFDP to figure out what particular flash device is attached. For example
> when there are different flashes with the same jedec id.
> 
> But since the last released kernel, we support a generic SFDP driver, which
> is used when there is no matching driver for the flash's jedec id.
> Theoretically, you can build your own flash device (with a unique id) and
> generate the sfdp tables for that one.
> 
How about older kernels versions ? Would those still support such (virtual ?)
flash devices ?

Thanks,
Guenter