linux-kernel - Re: [PATCH] pinctrl: tegra: use signed bitfields for optional fields

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Date:	Mon, 16 Mar 2015 21:30:02 +0100
From:	Stefan Agner <stefan@...er.ch>
To:	swarren@...dotorg.org
Cc:	linus.walleij@...aro.org, thierry.reding@...il.com,
	gnurou@...il.com, linux-gpio@...r.kernel.org,
	linux-tegra@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pinctrl: tegra: use signed bitfields for optional fields

On 2015-03-15 01:05, Stefan Agner wrote:
> Optional fields are set to -1 by various preprocessor macros. Make
> sure the struct fields can actually store them.
> 
> Signed-off-by: Stefan Agner <stefan@...er.ch>
> ---
> This lead to a lot of warnings when compiling the Tegra pinctrl drivers
> using LLVM/clang:
> 
> drivers/pinctrl/pinctrl-tegra124.c:2048:2: warning: implicit truncation from
> 'int' to bitfield changes value from -1 to 63 [-Wbitfield-constant-conversion]
>         MIPI_PAD_CTRL_PINGROUP(dsi_b,   0x820, 1, CSI, DSI_B)
>         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> drivers/pinctrl/pinctrl-tegra124.c:1807:18: note: expanded from macro
> 'MIPI_PAD_CTRL_PINGROUP'
>                 .rcv_sel_bit = -1,                                      \
>                                ^~
> 
> However, I did not check if this could actually lead to an unintended
> pin configuration...

Stephen, what do you think about this? While I think the patch  is the
right thing to do, it could actually introduce nasty regressions (stuff
which was working due to  "accidentally" wrong pin configuration)...

I need to admit that I did not actually run a kernel with that patch.

--
Stefan
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