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

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Date:	Thu, 2 Jun 2016 16:08:29 +0800
From:	Chen-Yu Tsai <wens@...e.org>
To:	Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:	Chen-Yu Tsai <wens@...e.org>, Ulf Hansson <ulf.hansson@...aro.org>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Hans de Goede <hdegoede@...hat.com>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH 1/3] mmc: fix mmc mode selection for HS-DDR and higher

On Thu, Jun 2, 2016 at 2:58 AM, Bjorn Andersson
<bjorn.andersson@...aro.org> wrote:
> On Sun, May 29, 2016 at 12:04 AM, Chen-Yu Tsai <wens@...e.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