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

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Date:   Wed, 16 Nov 2016 16:28:45 -0800
From:   Stefan Agner <stefan@...er.ch>
To:     Dong Aisheng <dongas86@...il.com>,
        Ulf Hansson <ulf.hansson@...aro.org>
Cc:     "Leonardo G. Veiga" <leogveiga@...il.com>,
        linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
        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.

On 2016-11-02 09:40, Stefan Agner wrote:
> On 2016-11-02 01:42, Dong Aisheng wrote:
>> 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.
> 
> Hm, I see what you are saying, the problem is that the core
> (sdhci_setup_host) falls back to 4-bit if SDHCI_QUIRK_FORCE_1_BIT_DATA
> is not set... Removing that should be fine for DT enabled SDHC drivers,
> since mmc_of_parse sets MMC_CAP_4_BIT_DATA. But not sure about drivers
> which parse dt on their own or still support platform data.... Those
> might rely on MMC_CAP_4_BIT_DATA being set by default...

Any thoughts on this?

Btw, I just realized that this used to work in 4.1 because back then the
device tree properties got parsed into struct esdhc_platform_data, which
does set the 1-bit quirk.. So this can be seen as a regression...

--
Stefan

> 
> --
> Stefan
> 
> 
> 
>>
>> 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