From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ulf Hansson Subject: Re: [PATCH] mmc: renesas_sdhi_internal_dmac: Add MMC_CAP_ERASE to Gen3 SoCs Date: Thu, 14 Nov 2019 13:48:41 +0100 Message-ID: References: <20191112134808.23546-1-erosca@de.adit-jv.com> <20191112204952.GA2976@kunai> <20191114113743.GA19656@vmlxhi-102.adit-jv.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Return-path: In-Reply-To: <20191114113743.GA19656@vmlxhi-102.adit-jv.com> Sender: linux-kernel-owner@vger.kernel.org To: Eugeniu Rosca Cc: Wolfram Sang , Wolfram Sang , Yoshihiro Shimoda , =?UTF-8?Q?Niklas_S=C3=B6derlund?= , Geert Uytterhoeven , Simon Horman , "linux-mmc@vger.kernel.org" , Linux Kernel Mailing List , Linux-Renesas , Eugeniu Rosca , Harish Jenny K N , Andrew Gabbasov List-Id: linux-mmc@vger.kernel.org On Thu, 14 Nov 2019 at 12:37, Eugeniu Rosca wrote: > > 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 wrote: > > > > > > On Tue, Nov 12, 2019 at 02:48:08PM +0100, Eugeniu Rosca wrote: > > > > From: Harish Jenny K N > > > > > > > > Enable MMC_CAP_ERASE capability in the driver to allow > > > > erase/discard/trim requests. > > > > > > > > Suggested-by: Andrew Gabbasov > > > > Signed-off-by: Harish Jenny K N > > > > [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 > > > > > > 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? Let's first take a step back, because I don't know how the HW busy detection works for your controller. I have noticed there is TMIO_STAT_CMD_BUSY bit being set for some variants, which seems to cause renesas_sdhi_wait_idle() to loop for a pre-defined number of loops/timeout. This looks scary, but I can't tell if it's really a problem. BTW, do you know what TMIO_STAT_CMD_BUSY actually is monitoring? I have also noticed that MMC_CAP_WAIT_WHILE_BUSY isn't set for any of the renesas/tmio variant hosts. Is that simply because the HW doesn't support this? Or because implementation is missing? If you want to run a test that stretches the behaviour on the timeout path, I would rather use an SD-card (the older the better). For eMMCs the erase likely translates to a trim/discard, which is far more quicker than a real erase - as is what happens on an old SD card. > > > > > 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 Kind regards Uffe