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Re: [PATCH 1/3] mmc: fix mmc mode selection for HS-DDR and higher

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  Re: [PATCH 1/3] mmc: fix mmc mode selection for HS-DDR and higher Bjorn Andersson <bjorn.andersson@linaro.org> - 2016-06-01 21:10 +0200
    Re: [PATCH 1/3] mmc: fix mmc mode selection for HS-DDR and higher Chen-Yu Tsai <wens@csie.org> - 2016-06-02 10:10 +0200

#1411481 — Re: [PATCH 1/3] mmc: fix mmc mode selection for HS-DDR and higher

On Sun, May 29, 2016 at 12:04 AM, Chen-Yu Tsai <wens@csie.org> wrote:
> When IS_ERR_VALUE was removed from the mmc core code, it was replaced
> with a simple not-zero check. This does not work, as the value checked
> is the return value for mmc_select_bus_width, which returns the set
> bit width on success. This made eMMC modes higher than HS-DDR unusable.
>
> Fix this by checking for a positive return value instead.

mmc_select_bus_width() can return 0 on "success" as well and the
previous check was !IS_ERR_VALUE(err), which coverts that. So I
believe these checks should be for err >= 0 rather than just > 0.


Either way this fixes the boot failures seen on my Qualcomm based
boards with v4.7-rc1.

Regards,
Bjorn

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#1411977

On Thu, Jun 2, 2016 at 2:58 AM, Bjorn Andersson
<bjorn.andersson@linaro.org> wrote:
> On Sun, May 29, 2016 at 12:04 AM, Chen-Yu Tsai <wens@csie.org> wrote:
>> When IS_ERR_VALUE was removed from the mmc core code, it was replaced
>> with a simple not-zero check. This does not work, as the value checked
>> is the return value for mmc_select_bus_width, which returns the set
>> bit width on success. This made eMMC modes higher than HS-DDR unusable.
>>
>> Fix this by checking for a positive return value instead.
>
> mmc_select_bus_width() can return 0 on "success" as well and the
> previous check was !IS_ERR_VALUE(err), which coverts that. So I
> believe these checks should be for err >= 0 rather than just > 0.

From the comments above the function:
"Zero is returned instead of error value if the wide width is not supported."

The documents I found, which were more vendor datasheets, only list
bit widths 4 and 8 for high speed SDR/DDR and HS200.

Not sure what the MMC spec actually says though, as I do not have
it.

Regards
ChenYu

>
>
> Either way this fixes the boot failures seen on my Qualcomm based
> boards with v4.7-rc1.
>
> Regards,
> Bjorn

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