linux-kernel - Re: [PATCH] mmc: dw_mmc: Fix IDMAC operation with pages bigger than 4K

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Message-ID: <CAPDyKFrviGd6ECV-8LOENgepUZZ1OV2j+d+H5NPCjnHYfrijWQ@mail.gmail.com>
Date: Wed, 28 Aug 2024 17:23:28 +0200
From: Ulf Hansson <ulf.hansson@...aro.org>
To: Sam Protsenko <semen.protsenko@...aro.org>
Cc: Jaehoon Chung <jh80.chung@...sung.com>, Arnd Bergmann <arnd@...db.de>, 
	Christoph Hellwig <hch@....de>, Chris Ball <cjb@...top.org>, Will Newton <will.newton@...il.com>, 
	Matt Fleming <matt@...sole-pimps.org>, Christian Brauner <brauner@...nel.org>, 
	Jens Axboe <axboe@...nel.dk>, Sumit Semwal <sumit.semwal@...aro.org>, 
	Dan Carpenter <dan.carpenter@...aro.org>, Anders Roxell <anders.roxell@...aro.org>, 
	Naresh Kamboju <naresh.kamboju@...aro.org>, linux-mmc@...r.kernel.org, 
	linux-block <linux-block@...r.kernel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmc: dw_mmc: Fix IDMAC operation with pages bigger than 4K

On Thu, 7 Mar 2024 at 00:20, Sam Protsenko <semen.protsenko@...aro.org> wrote:
>
> Commit 616f87661792 ("mmc: pass queue_limits to blk_mq_alloc_disk") [1]
> revealed the long living issue in dw_mmc.c driver, existing since the
> time when it was first introduced in commit f95f3850f7a9 ("mmc: dw_mmc:
> Add Synopsys DesignWare mmc host driver."), also making kernel boot
> broken on platforms using dw_mmc driver with 16K or 64K pages enabled,
> with this message in dmesg:
>
>     mmcblk: probe of mmc0:0001 failed with error -22
>
> That's happening because mmc_blk_probe() fails when it calls
> blk_validate_limits() consequently, which returns the error due to
> failed max_segment_size check in this code:
>
>     /*
>      * The maximum segment size has an odd historic 64k default that
>      * drivers probably should override.  Just like the I/O size we
>      * require drivers to at least handle a full page per segment.
>      */
>     ...
>     if (WARN_ON_ONCE(lim->max_segment_size < PAGE_SIZE))
>         return -EINVAL;
>
> In case when IDMAC (Internal DMA Controller) is used, dw_mmc.c always
> sets .max_seg_size to 4 KiB:
>
>     mmc->max_seg_size = 0x1000;
>
> The comment in the code above explains why it's incorrect. Arnd
> suggested setting .max_seg_size to .max_req_size to fix it, which is
> also what some other drivers are doing:
>
>    $ grep -rl 'max_seg_size.*=.*max_req_size' drivers/mmc/host/ | \
>      wc -l
>    18
>
> This change is not only fixing the boot with 16K/64K pages, but also
> leads to a better MMC performance. The linear write performance was
> tested on E850-96 board (eMMC only), before commit [1] (where it's
> possible to boot with 16K/64K pages without this fix, to be able to do
> a comparison). It was tested with this command:
>
>     # dd if=/dev/zero of=somefile bs=1M count=500 oflag=sync
>
> Test results are as follows:
>
>   - 4K pages,  .max_seg_size = 4 KiB:                   94.2 MB/s
>   - 4K pages,  .max_seg_size = .max_req_size = 512 KiB: 96.9 MB/s
>   - 16K pages, .max_seg_size = 4 KiB:                   126 MB/s
>   - 16K pages, .max_seg_size = .max_req_size = 2 MiB:   128 MB/s
>   - 64K pages, .max_seg_size = 4 KiB:                   138 MB/s
>   - 64K pages, .max_seg_size = .max_req_size = 8 MiB:   138 MB/s
>
> Unfortunately, SD card controller is not enabled in E850-96 yet, so it
> wasn't possible for me to run the test on some cheap SD cards to check
> this patch's impact on those. But it's possible that this change might
> also reduce the writes count, thus improving SD/eMMC longevity.
>
> All credit for the analysis and the suggested solution goes to Arnd.
>
> [1] https://lore.kernel.org/all/20240215070300.2200308-18-hch@lst.de/
>
> Fixes: f95f3850f7a9 ("mmc: dw_mmc: Add Synopsys DesignWare mmc host driver.")
> Suggested-by: Arnd Bergmann <arnd@...db.de>
> Reported-by: Linux Kernel Functional Testing <lkft@...aro.org>
> Closes: https://lore.kernel.org/all/CA+G9fYtddf2Fd3be+YShHP6CmSDNcn0ptW8qg+stUKW+Cn0rjQ@mail.gmail.com/
> Signed-off-by: Sam Protsenko <semen.protsenko@...aro.org>

Applied for fixes and by adding a stable-tag, thanks!

Kind regards
Uffe


> ---
>  drivers/mmc/host/dw_mmc.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index 8e2d676b9239..cccd5633ff40 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -2951,8 +2951,8 @@ static int dw_mci_init_slot(struct dw_mci *host)
>         if (host->use_dma == TRANS_MODE_IDMAC) {
>                 mmc->max_segs = host->ring_size;
>                 mmc->max_blk_size = 65535;
> -               mmc->max_seg_size = 0x1000;
> -               mmc->max_req_size = mmc->max_seg_size * host->ring_size;
> +               mmc->max_req_size = DW_MCI_DESC_DATA_LENGTH * host->ring_size;
> +               mmc->max_seg_size = mmc->max_req_size;
>                 mmc->max_blk_count = mmc->max_req_size / 512;
>         } else if (host->use_dma == TRANS_MODE_EDMAC) {
>                 mmc->max_segs = 64;
> --
> 2.39.2
>