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

[Michael Walle <michael@walle.cc>]

Am 2023-01-02 17:23, schrieb Guenter Roeck:
> 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 ?

No with older kernels you'd be out of luck. They will just print 
"unknown flash
id" and skip the device.

-michael