Re: [PATCH 2/2] mmc: mmci_sdmmc: fix DMA API warning max segment size

From: Ulf Hansson <ulf.hansson@linaro.org>
To: Ludovic Barre <ludovic.barre@st.com>
Cc: Rob Herring <robh+dt@kernel.org>,
	Srini Kandagatla <srinivas.kandagatla@linaro.org>,
	Maxime Coquelin <mcoquelin.stm32@gmail.com>,
	Alexandre Torgue <alexandre.torgue@st.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	DTML <devicetree@vger.kernel.org>,
	"linux-mmc@vger.kernel.org" <linux-mmc@vger.kernel.org>,
	linux-stm32@st-md-mailman.stormreply.com
Subject: Re: [PATCH 2/2] mmc: mmci_sdmmc: fix DMA API warning max segment size
Date: Thu, 28 May 2020 12:14:28 +0200	[thread overview]
Message-ID: <CAPDyKForRHZFGEzn=5OVY8YP6okFj7G2e6QTJFH5-Q_xP3QLBw@mail.gmail.com> (raw)
In-Reply-To: <20200526155103.12514-3-ludovic.barre@st.com>

On Tue, 26 May 2020 at 17:51, Ludovic Barre <ludovic.barre@st.com> wrote:
>
> Turning on CONFIG_DMA_API_DEBUG_SG results in the following warning:
> WARNING: CPU: 1 PID: 85 at kernel/dma/debug.c:1302 debug_dma_map_sg+0x2a0/0x3cc
> mmci-pl18x 58005000.sdmmc: DMA-API: mapping sg segment longer than device claims to support [len=126976] [max=65536]
>
> dma api debug checks and compares the segment size to
> dma_get_max_seg_size (dev->dma_parms->max_segment_size),
> the sdmmc variant has an internal DMA and should define
> its max_segment_size constraint to avoid this warning.
>
> This Patch defines the dev->dma_parms->max_segment_size
> with the constraint already set for mmc core
> (host->mmc->max_seg_size).
>
> Signed-off-by: Ludovic Barre <ludovic.barre@st.com>

Applied for next, thanks!

Note, a manual backport is needed for stable, as
dma_set_max_seg_size() will fail for older kernels.
We needed to revert 9495b7e92f7 ("driver core: platform: Initialize
dma_parms for platform devices"), for stable kernels [1].

Kind regards
Uffe

[1]
https://lkml.org/lkml/2020/5/26/1216

> ---
>  drivers/mmc/host/mmci_stm32_sdmmc.c | 11 +++++------
>  1 file changed, 5 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/mmc/host/mmci_stm32_sdmmc.c b/drivers/mmc/host/mmci_stm32_sdmmc.c
> index 2965b1c062e1..51db30acf4dc 100644
> --- a/drivers/mmc/host/mmci_stm32_sdmmc.c
> +++ b/drivers/mmc/host/mmci_stm32_sdmmc.c
> @@ -119,20 +119,19 @@ static void sdmmc_idma_unprep_data(struct mmci_host *host,
>  static int sdmmc_idma_setup(struct mmci_host *host)
>  {
>         struct sdmmc_idma *idma;
> +       struct device *dev = mmc_dev(host->mmc);
>
> -       idma = devm_kzalloc(mmc_dev(host->mmc), sizeof(*idma), GFP_KERNEL);
> +       idma = devm_kzalloc(dev, sizeof(*idma), GFP_KERNEL);
>         if (!idma)
>                 return -ENOMEM;
>
>         host->dma_priv = idma;
>
>         if (host->variant->dma_lli) {
> -               idma->sg_cpu = dmam_alloc_coherent(mmc_dev(host->mmc),
> -                                                  SDMMC_LLI_BUF_LEN,
> +               idma->sg_cpu = dmam_alloc_coherent(dev, SDMMC_LLI_BUF_LEN,
>                                                    &idma->sg_dma, GFP_KERNEL);
>                 if (!idma->sg_cpu) {
> -                       dev_err(mmc_dev(host->mmc),
> -                               "Failed to alloc IDMA descriptor\n");
> +                       dev_err(dev, "Failed to alloc IDMA descriptor\n");
>                         return -ENOMEM;
>                 }
>                 host->mmc->max_segs = SDMMC_LLI_BUF_LEN /
> @@ -143,7 +142,7 @@ static int sdmmc_idma_setup(struct mmci_host *host)
>                 host->mmc->max_seg_size = host->mmc->max_req_size;
>         }
>
> -       return 0;
> +       return dma_set_max_seg_size(dev, host->mmc->max_seg_size);
>  }
>
>  static int sdmmc_idma_start(struct mmci_host *host, unsigned int *datactrl)
> --
> 2.17.1
>