linux-kernel - Re: [PATCH] gpio: pca953x: Fix NBANK calculation for PCA9536

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Date:	Mon, 13 Jun 2016 14:34:04 +0530
From:	Vignesh R <vigneshr@...com>
To:	Linus Walleij <linus.walleij@...aro.org>
CC:	Alexandre Courbot <gnurou@...il.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] gpio: pca953x: Fix NBANK calculation for PCA9536



On Monday 13 June 2016 12:52 PM, Linus Walleij wrote:
> On Thu, Jun 9, 2016 at 7:32 AM, Vignesh R <vigneshr@...com> wrote:
> 
>> NBANK() macro assumes that ngpios is a multiple of 8(BANK_SZ) and
>> hence results in 0 banks for PCA9536 which has just 4 gpios. This is
>> wrong as PCA9356 has 1 bank with 4 gpios. This results in uninitialized
>> PCA953X_INVERT register. Fix this by using DIV_ROUND_UP macro in
>> NBANK().
>>
>> Cc: stable@...r.kernel.org
>> Signed-off-by: Vignesh R <vigneshr@...com>
> 
> Patch applied.
> 
> Is this really a regression or affecting systems in development?
> 
> Which machine/device tree makes this problematic?
> 

I observed this on am335x-icev2 evm which is system in development.
Basically, variable with uninitialized value (junk) gets written to
PCA953X_INVERT register(in device_pca953x_init()) causing driver to
report wrong gpio pin status. So, this bug will affect any platform with
PCA9536 chip. Quick grep on arch/*/boot/dts/ folder shows one platform
already using pca9536 chip. Hence, I added Cc to stable kernel.

-- 
Regards
Vignesh