Re: [PATCH] mtd: spi-nor: intel-spi: Add support for second flash chip

[Pratyush Yadav <p.yadav@xxxxxx>]

+Mark, linux-spi list,

On 03/06/21 02:07PM, Mika Westerberg wrote:
> Hi Tudor,
> 
> On Mon, May 31, 2021 at 02:29:59PM +0300, Mika Westerberg wrote:
> > Hi guys,
> > 
> > On Wed, May 26, 2021 at 01:28:16PM +0300, Mika Westerberg wrote:
> > > Hi,
> > > 
> > > On Wed, May 26, 2021 at 11:31:58AM +0200, Michael Walle wrote:
> > > > > Oh, I see now this commit:
> > > > > 
> > > > > a314f6367787 ("mtd: spi-nor: Convert cadence-quadspi to use spi-mem
> > > > > framework")
> > > > > 
> > > > > So "SPI MEM" means generic SPI subsystem for memory mapped devices.
> > > > > Unfortunately Intel controller at least is not capable of running
> > > > > generic SPI transactions. It only supports accessing SPI-NOR flashes and
> > > > > for those there is small set of commands that supports. I don't think it
> > > > > is even possible to convert the driver to generic SPI subsystem.
> > > > 
> > > > AFAIK it stands for SPI memory device (memory mapped is not a requirement).
> > > > Eg. spi-nxp-fspi doesn't support generic SPI devices either, but just SPI
> > > > flashes. So I'd guess SPI MEM is exactly what you are looking for.
> > > 
> > > OK, I see that there is ->mem_ops that can be used to implement
> > > different higher level commands. What I'm not seeing is that how the
> > > child SPI flash is created using this scheme? DeviceTree and ACPI are
> > > supported fine but what about scanning? I mean the intel_spi driver has
> > > this:
> > > 
> > >   spi_nor_scan(&ispi->nor, NULL, &hwcaps);
> > > 
> > > But if the driver is to be moved under drivers/spi/* you can't really
> > > call these functions anymore or can you? Or the point is to keep the
> > > driver under controllers/ and just call spi_nor_scan(), and in addition
> > > implement the new mem_ops?
> > > 
> > > Thanks in advance and sorry about many questions but there does not seem
> > > to be a conversion guide nor any (non-DT/ACPI) examples that I can take
> > > a look. :-)
> > 
> > Can you provide some guidance here? So in order to use the generic SPI
> > subsystem with "SPI MEM" parts of it, I would need to be able to create
> > the child SPI-NOR flash device without using ACPI or DT (as these
> > systems do not have any ACPI/DT description), or use spi_nor_scan() but
> > none of the driver under drivers/spi are calling it.
> 
> As the main SPI-NOR maintainer, what's your take on this?

I think this is more of a SPI or SPI MEM question, and less of a SPI NOR 
question. SPI MEM would call spi_nor_probe() which in turn calls 
spi_nor_scan().

So the question that needs to be answered is how to probe SPI MEM based
drivers without ACPI/DT.

> 
> Thanks!

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.