[U-Boot] [PATCH v2 14/38] spi: Add support for memory-mapped flash

[Simon Glass]

Hi,

On Thu, 17 Oct 2019 at 08:28, Simon Glass <sjg at chromium.org> wrote:
>
> Hi Vignesh,
>
> On Wed, 16 Oct 2019 at 04:28, Vignesh Raghavendra <vigneshr at ti.com> wrote:
> >
> > Hi Simon,
> >
> > On 12/10/19 10:03 AM, Bin Meng wrote:
> > > Hi Simon,
> > >
> > > On Sat, Oct 12, 2019 at 11:08 AM Simon Glass <sjg at chromium.org> wrote:
> > >>
> > >> Hi Bin,
> > >>
> > >> On Wed, 9 Oct 2019 at 07:55, Bin Meng <bmeng.cn at gmail.com> wrote:
> > >>>
> > >>> Hi Simon,
> > >>>
> > >>> On Wed, Sep 25, 2019 at 10:12 PM Simon Glass <sjg at chromium.org> wrote:
> > >>>>
> > >>>> On x86 platforms the SPI flash can be mapped into memory so that the
> > >>>> contents can be read with normal memory accesses.
> > >>>>
> > >>>> Add a new SPI flash method to find the location of the SPI flash in
> > >>>> memory. This differs from the existing device-tree "memory-map" mechanism
> > >>>> in that the location can be discovered at run-time.
> > >>>>
> >
> > Whats is the usecase? Why can't spi_flash_read() be used instead?
> > Flash + Controller driver can underneath take care of using memory
> > mapped mode to read data from flash right while making sure that access
> > is within valid window?
>
> I can see spi_flash_read_dm() but it does not support returning a
> pointer to the data, only reading it.
>
> Also I cannot find any documentation about any of this. I've been
> looking in the doc/ directory.
>
> I found the spi_mem.h file but it doesn't mention the meaning of the
> in and out buffer pointers so I don't know how to use them.
>
> Is there an API missing or just comments/documentation?

Apart from this I have found that the ich_spi driver does not work for
APL since it apparently only supports 'hardware sequencing'. I did try
getting software sequencing to work, but no dice.

In addition, I found that enabling SPI flash, etc. added about 6KB of code!

So I think it might be best to have two SPI drivers for x86 - one for
software sequencing and one for hardware?

Regards,
Simon