Re: [PATCH 1/3] dt-bindings: mmc: mmci: add a property to disable DMA LLI

Ulf Hansson
2022-03-11T15:47:32Z

On Thu, 10 Mar 2022 at 17:00, Yann Gautier <yann.gautier@foss.st.com> wrote:
>
> On 3/8/22 11:57, Ulf Hansson wrote:
> > Hi Yann,
> >
> > On Fri, 4 Mar 2022 at 14:52, Yann Gautier <yann.gautier@foss.st.com> wrote:
> >>
> >> On STMicroelectronics variant of PL18x, the DMA Linked Lists are supported
> >> starting from revision v2 of the peripheral. But it has limitations,
> >> as all the buffers should be aligned on block size (except the last one).
> >> But this cannot be guaranteed with SDIO. We should then have a property
> >> to disable the support of LLI.
> >
> > Indeed, the buffer handling with SDIO is somewhat special, which also
> > has been discussed several times on LKML before. In principle, we need
> > the SDIO func drivers to respect buffer limitations that should be
> > specified by the mmc host drivers. Quite similar to what we already
> > have for block devices, like ->max_seg_size, ->max_seg, etc, that is
> > set per mmc host.
> >
> > I realize that implementing something like the above requires bigger
> > changes, which is why mmc host drivers instead validates the sglists
> > and the elements. In some cases that means returning an error code and
> > in others it could mean falling back to a non-DMA based I/O mode.
> >
> > For the stm32_sdmmc variant, it looks like the sglist validation is
> > being managed in sdmmc_idma_validate_data() already. Can it be
> > extended to cover this case too, rather than using a DT property?
> >
> > Kind regards
> > Uffe
>
> Hi Ulf,
>
> OK, I'll check what can be done for this. Patches 1 and 2 can be
> dropped, they will be reworked.

Okay.

> But patch 3 of this series could be taken, as not linked to LLI
> management. Should I push it again alone, or could you review it directly?

I have some comments/questions on it, but perhaps it makes it easier
for people to follow the discussion if it is done separately. So
please push it alone, then I will review it.

[...]

Kind regards
Uffe