linux-kernel - Re: [PATCHv10 4/6] drm/meson: Fix overflow implicit truncation warnings

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Message-ID: <65531cb4-efff-1e0e-2bac-7c7759ff55cd@quicinc.com>
Date:   Thu, 28 Apr 2022 08:33:15 +0530
From:   Sai Prakash Ranjan <quic_saipraka@...cinc.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Marc Zyngier <maz@...nel.org>,
        "Trilok Soni" <quic_tsoni@...cinc.com>,
        <quic_psodagud@...cinc.com>, gregkh <gregkh@...uxfoundation.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        kernel test robot <lkp@...el.com>
Subject: Re: [PATCHv10 4/6] drm/meson: Fix overflow implicit truncation
 warnings

On 4/27/2022 9:29 PM, Arnd Bergmann wrote:
> On Thu, Feb 24, 2022 at 7:07 AM Sai Prakash Ranjan
> <quic_saipraka@...cinc.com> wrote:
>> Fix -Woverflow warnings for drm/meson driver which is a result
>> of moving arm64 custom MMIO accessor macros to asm-generic function
>> implementations giving a bonus type-checking now and uncovering these
>> overflow warnings.
>>
>> drivers/gpu/drm/meson/meson_viu.c: In function ‘meson_viu_init’:
>> drivers/gpu/drm/meson/meson_registers.h:1826:48: error: large integer implicitly truncated to unsigned type [-Werror=overflow]
>>   #define  VIU_OSD_BLEND_REORDER(dest, src)      ((src) << (dest * 4))
>>                                                  ^
>> drivers/gpu/drm/meson/meson_viu.c:472:18: note: in expansion of macro ‘VIU_OSD_BLEND_REORDER’
>>     writel_relaxed(VIU_OSD_BLEND_REORDER(0, 1) |
>>                    ^~~~~~~~~~~~~~~~~~~~~
>>
>> Cc: Arnd Bergmann <arnd@...db.de>
>> Cc: Neil Armstrong <narmstrong@...libre.com>
>> Reported-by: kernel test robot <lkp@...el.com>
>> Signed-off-by: Sai Prakash Ranjan <quic_saipraka@...cinc.com>
> Reviewed-by: Arnd Bergmann <arnd@...db.de>
>
> It took me a bit to understand why we got the warning in the first place, but I
> should have just read the patch description, it's all there....

Right :)

Thanks,
Sai