linux-kernel - Re: [PATCH] mmc: pwrseq_simple: Fix incorrect handling of GPIO bitmap

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Date:   Wed, 26 Sep 2018 10:14:43 +0200
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Janusz Krzysztofik <jmkrzyszt@...il.com>,
        Linus Walleij <linus.walleij@...aro.org>
Cc:     Ulf Hansson <ulf.hansson@...aro.org>, linux-mmc@...r.kernel.org,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        Krzysztof Kozlowski <krzk@...nel.org>,
        Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH] mmc: pwrseq_simple: Fix incorrect handling of GPIO
 bitmap

Hi Janusz,

On 2018-09-25 21:24, Janusz Krzysztofik wrote:
> Commit b9762bebc633 ("gpiolib: Pass bitmaps, not integer arrays, to
> get/set array") changed the way GPIO values are passed to
> gpiod_get/set_array_value() and friends.  The updated code of
> mmc_pwrseq_simple_set_gpios_value() incorrectly uses the 'value'
> argument as a bitmap of GPIO values and assigns it directly to the
> 'values' bitmap variable passed to gpiod_set_array_value_cansleep()
> instead of filling that bitmap with bits equal to the 'value' argument.
> As a result, boot hanging caused by incorrectly handled MMC device
> has been observed.
>
> As a side effect of that incorrect interpreation of the 'value'
> argument, wrong assumption is taken about the 'values' bitmap size
> never exceding the number of bits of the 'value' argument type.
>
> Fix it.
>
> Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Signed-off-by: Janusz Krzysztofik <jmkrzyszt@...il.com>
> ---
> Hi,
>
> I hope I've finally identified the root cause of the boot hang reported
> by Marek Szyprowski.  I've reviewed the code of other divers updated for
> the modified GPIO API and found no more issues of that kind.
>
> Marek, can you please test this fix on top of next-20180920 with the fix
> "gpiolib: Fix missing updates of bitmap index" also applied?

Yes, I've just did such test (next-20180920 + "gpiolib: Fix missing
updates of bitmap index" + "mmc: pwrseq_simple: Fix incorrect handling
of GPIO bitmap") and sadly it doesn't fix the boot hang.

With some more debugs in mmc_pwrseq_simple I've noticed that
gpiod_set_array_value_cansleep() never ends and busyloops somewhere.
I'm checking this now.

> I've assumed this fix, if tested successfully, will be merged via GPIO
> tree, hence I've selected Linus as the main recipient of this message.
>
> Thanks,
> Janusz
>
>   drivers/mmc/core/pwrseq_simple.c | 13 +++++++++++--
>   1 file changed, 11 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/mmc/core/pwrseq_simple.c b/drivers/mmc/core/pwrseq_simple.c
> index 7f882a2bb872..ece34c734693 100644
> --- a/drivers/mmc/core/pwrseq_simple.c
> +++ b/drivers/mmc/core/pwrseq_simple.c
> @@ -40,13 +40,22 @@ static void mmc_pwrseq_simple_set_gpios_value(struct mmc_pwrseq_simple *pwrseq,
>   	struct gpio_descs *reset_gpios = pwrseq->reset_gpios;
>   
>   	if (!IS_ERR(reset_gpios)) {
> -		DECLARE_BITMAP(values, BITS_PER_TYPE(value));
> +		unsigned long *values;
>   		int nvalues = reset_gpios->ndescs;
>   
> -		values[0] = value;
> +		values = bitmap_alloc(nvalues, GFP_KERNEL);
> +		if (!values)
> +			return;
> +
> +		if (value)
> +			bitmap_fill(values, nvalues);
> +		else
> +			bitmap_zero(values, nvalues);
>   
>   		gpiod_set_array_value_cansleep(nvalues, reset_gpios->desc,
>   					       reset_gpios->info, values);
> +
> +		kfree(values);
>   	}
>   }
>   

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland