linux-kernel - Re: [PATCH] mmc: jz4740: Apply DMA engine limits to maximum segment size

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Message-ID: <CAPDyKFpuD1m68SRuCYj0q+KU2Ua1Jt+f3upbLavs8x4HS0-szA@mail.gmail.com>
Date:   Thu, 21 Apr 2022 15:54:16 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Aidan MacDonald <aidanmacdonald.0x0@...il.com>
Cc:     paul@...pouillou.net, linux-mips@...r.kernel.org,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mmc: jz4740: Apply DMA engine limits to maximum segment size

On Mon, 11 Apr 2022 at 17:37, Aidan MacDonald
<aidanmacdonald.0x0@...il.com> wrote:
>
> Do what is done in other DMA-enabled MMC host drivers (cf. host/mmci.c) and
> limit the maximum segment size based on the DMA engine's capabilities. This
> is needed to avoid warnings like the following with CONFIG_DMA_API_DEBUG=y.
>
> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 21 at kernel/dma/debug.c:1162 debug_dma_map_sg+0x2f4/0x39c
> DMA-API: jz4780-dma 13420000.dma-controller: mapping sg segment longer than device claims to support [len=98304] [max=65536]
> CPU: 0 PID: 21 Comm: kworker/0:1H Not tainted 5.18.0-rc1 #19
> Workqueue: kblockd blk_mq_run_work_fn
> Stack : 81575aec 00000004 80620000 80620000 80620000 805e7358 00000009 801537ac
>         814c832c 806276e3 806e34b4 80620000 81575aec 00000001 81575ab8 09291444
>         00000000 00000000 805e7358 81575958 ffffffea 8157596c 00000000 636f6c62
>         6220646b 80387a70 0000000f 6d5f6b6c 80620000 00000000 81575ba4 00000009
>         805e170c 80896640 00000001 00010000 00000000 00000000 00006098 806e0000
>         ...
> Call Trace:
> [<80107670>] show_stack+0x84/0x120
> [<80528cd8>] __warn+0xb8/0xec
> [<80528d78>] warn_slowpath_fmt+0x6c/0xb8
> [<8016f1d4>] debug_dma_map_sg+0x2f4/0x39c
> [<80169d4c>] __dma_map_sg_attrs+0xf0/0x118
> [<8016a27c>] dma_map_sg_attrs+0x14/0x28
> [<804f66b4>] jz4740_mmc_prepare_dma_data+0x74/0xa4
> [<804f6714>] jz4740_mmc_pre_request+0x30/0x54
> [<804f4ff4>] mmc_blk_mq_issue_rq+0x6e0/0x7bc
> [<804f5590>] mmc_mq_queue_rq+0x220/0x2d4
> [<8038b2c0>] blk_mq_dispatch_rq_list+0x480/0x664
> [<80391040>] blk_mq_do_dispatch_sched+0x2dc/0x370
> [<80391468>] __blk_mq_sched_dispatch_requests+0xec/0x164
> [<80391540>] blk_mq_sched_dispatch_requests+0x44/0x94
> [<80387900>] __blk_mq_run_hw_queue+0xb0/0xcc
> [<80134c14>] process_one_work+0x1b8/0x264
> [<80134ff8>] worker_thread+0x2ec/0x3b8
> [<8013b13c>] kthread+0x104/0x10c
> [<80101dcc>] ret_from_kernel_thread+0x14/0x1c
>
> ---[ end trace 0000000000000000 ]---
>
> Signed-off-by: Aidan MacDonald <aidanmacdonald.0x0@...il.com>

Applied for next, thanks!

Kind regards
Uffe


> ---
>  drivers/mmc/host/jz4740_mmc.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/drivers/mmc/host/jz4740_mmc.c b/drivers/mmc/host/jz4740_mmc.c
> index 7ab1b38a7be5..b1d563b2ed1b 100644
> --- a/drivers/mmc/host/jz4740_mmc.c
> +++ b/drivers/mmc/host/jz4740_mmc.c
> @@ -247,6 +247,26 @@ static int jz4740_mmc_acquire_dma_channels(struct jz4740_mmc_host *host)
>                 return PTR_ERR(host->dma_rx);
>         }
>
> +       /*
> +        * Limit the maximum segment size in any SG entry according to
> +        * the parameters of the DMA engine device.
> +        */
> +       if (host->dma_tx) {
> +               struct device *dev = host->dma_tx->device->dev;
> +               unsigned int max_seg_size = dma_get_max_seg_size(dev);
> +
> +               if (max_seg_size < host->mmc->max_seg_size)
> +                       host->mmc->max_seg_size = max_seg_size;
> +       }
> +
> +       if (host->dma_rx) {
> +               struct device *dev = host->dma_rx->device->dev;
> +               unsigned int max_seg_size = dma_get_max_seg_size(dev);
> +
> +               if (max_seg_size < host->mmc->max_seg_size)
> +                       host->mmc->max_seg_size = max_seg_size;
> +       }
> +
>         return 0;
>  }
>
> --
> 2.35.1
>