linux-kernel - Re: [PATCH] sdhci-esdhc-imx: fix bus-width for 1-bit operation.

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Date:   Wed, 2 Nov 2016 16:42:38 +0800
From:   Dong Aisheng <dongas86@...il.com>
To:     "Leonardo G. Veiga" <leogveiga@...il.com>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stefan Agner <stefan@...er.ch>, raul.munoz@...adex.com,
        leonardo.veiga@...adex.com, Haibo Chen <haibo.chen@....com>
Subject: Re: [PATCH] sdhci-esdhc-imx: fix bus-width for 1-bit operation.

Hi Leonardo,

On Tue, Nov 1, 2016 at 11:58 PM, Leonardo G. Veiga <leogveiga@...il.com> wrote:
> From: Leonardo Graboski Veiga <leonardo.veiga@...adex.com>
>
> The 1-bit operation mode, enabled by seeting the 'bus-width' property of
> the device tree 'esdhc' node to <1>, not work while using SD card.
>
> The behavior is only noticed when only the data pin 0 is connected to the
> hardware. A series of kernel errors are printed to the console, all of them
> returning the following error message followed by some explanation:
> mmcblk0: error -84 transferring data
>
> If four data lines are connected, it ignores the device-tree
> property and works in 4-bit mode of operation without errors. The hardware
> used for testing does not support 8-bit mode.
>
> Check the 'bus-width' property and if set to <1>, enable the
> SDHCI_QUIRK_FORCE_1_BIT_DATA quirk.
>
> Signed-off-by: Leonardo Graboski Veiga <leonardo.veiga@...adex.com>
> ---
>  drivers/mmc/host/sdhci-esdhc-imx.c | 4 ++++
>  1 file changed, 4 insertions(+)
>
> diff --git a/drivers/mmc/host/sdhci-esdhc-imx.c b/drivers/mmc/host/sdhci-esdhc-imx.c
> index c9fbc4c3..88d7d22 100644
> --- a/drivers/mmc/host/sdhci-esdhc-imx.c
> +++ b/drivers/mmc/host/sdhci-esdhc-imx.c
> @@ -1003,6 +1003,10 @@ sdhci_esdhc_imx_probe_dt(struct platform_device *pdev,
>                 host->quirks2 |= SDHCI_QUIRK2_NO_1_8_V;
>         }
>
> +       if (!of_property_read_u32(np, "bus-width", &boarddata->max_bus_width)
> +               && boarddata->max_bus_width == 1)
> +               host->quirks |= SDHCI_QUIRK_FORCE_1_BIT_DATA;
> +

This looks like a common SDHCI driver issue that it assumes the default
bus-width as 4 bit if no SDHCI_QUIRK_FORCE_1_BIT_DATA specified.
        if (!(host->quirks & SDHCI_QUIRK_FORCE_1_BIT_DATA))
                mmc->caps |= MMC_CAP_4_BIT_DATA;

And I'm not sure Andrian or Ulf would like to see people keep using this quirk.
IMHO we probably could totally remove it since bus-width already tells
what the driver needs.

Andrian & Ulf,
Comments?

>         /* call to generic mmc_of_parse to support additional capabilities */
>         ret = mmc_of_parse(host->mmc);
>         if (ret)
> --
> 2.7.4
>

Regards
Dong Aisheng