Re: [PATCH] mmc: renesas_sdhi_internal_dmac: Add MMC_CAP_ERASE to Gen3 SoCs

[Ulf Hansson]

On Tue, 12 Nov 2019 at 21:49, Wolfram Sang <wsa@xxxxxxxxxxxxx> wrote:
>
> On Tue, Nov 12, 2019 at 02:48:08PM +0100, Eugeniu Rosca wrote:
> > From: Harish Jenny K N <harish_kandiga@xxxxxxxxxx>
> >
> > Enable MMC_CAP_ERASE capability in the driver to allow
> > erase/discard/trim requests.
> >
> > Suggested-by: Andrew Gabbasov <andrew_gabbasov@xxxxxxxxxx>
> > Signed-off-by: Harish Jenny K N <harish_kandiga@xxxxxxxxxx>
> > [erosca: Forward-port and test on v5.4-rc7 using H3ULCB-KF:
> >          "blkdiscard /dev/mmcblk0" passes with this patch applied
> >          and complains otherwise:
> >        "BLKDISCARD ioctl failed: Operation not supported"]
> > Signed-off-by: Eugeniu Rosca <erosca@xxxxxxxxxxxxxx>
>
> Looks good to me. Just a generic question, probably more for Ulf:
>
> Why does this CAP_ERASE exist? As I understand, the driver only needs to
> set the flag and no further handling is required. Why would a driver not
> set this flag and not support erase/trim commands?

I am working on removing the cap, altogether. Step by step, this is
getting closer now.

The main problem has been about busy detect timeouts, as an erase
command may have a very long busy timeout. On the host side, they
typically need to respect the cmd->busy_timeout for the request, and
if it can't because of some HW limitation, it needs to set
mmc->max_busy_timeout.

Once that is fixed for all, we can drop CAP_ERASE.

Kind regards
Uffe