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

[Simon Glass]

Hi Vignesh,

On Fri, 18 Oct 2019 at 03:48, Vignesh Raghavendra <vigneshr at ti.com> wrote:
>
>
>
> On 18/10/19 7:52 AM, Simon Glass wrote:
> > 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.
> >>
>
> No, I was merely suggesting to use spi_flash_read_dm() (which underneath
> can be implemented by spi_mem_ops) to get data from flash instead of
> using get_mmap() to get MMIO pointer and then reading the data using
> that potiner.

OK I see.

>
> >> 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?
> >
>
> spi-mem.h has struct and APIs documented as kerneldoc:
> https://elixir.bootlin.com/u-boot/latest/source/include/spi-mem.h#L72
> https://elixir.bootlin.com/u-boot/latest/source/include/spi-mem.h#L168

Yes I see that, but these appear to be undocumented, or not documented
enough to understand their purpose/use:

opcode
in
out

Could you please update that?

>
> Note that clients should still use spi_flash_*() APIs to interact with
> flash. spi_mem_ops are not an alternative to spi_flash_*() APIs which
> are used by other drivers to read/write data from/to flash. This
> continues to be the same.

OK.

Regards,
Simon