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

[Eugeniu Rosca]

Hi everyone,

On Thu, Nov 14, 2019 at 11:56:23AM +0100, Ulf Hansson wrote:
> 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.

FWIW we've discussed such concerns internally, based on past commits
which either disable [1-2] busy timeouts or increase their value [3].

To get a feeling if this is relevant for R-Car3, I've run blkdiscard on
a 64 GiB eMMC without noticing any issues on v5.4-rc7. Hopefully this
is sufficient as testing?

> 
> Once that is fixed for all, we can drop CAP_ERASE.
> 
> Kind regards
> Uffe

[1] 93caf8e69eac76 ("omap_hsmmc: add erase capability")
[2] b13d1f0f9ad64b ("mmc: omap: Add erase capability")
[3] ec30f11e821f2d ("mmc: rtsx_usb: Use the provided busy timeout from the mmc core")

-- 
Best Regards,
Eugeniu