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References: <20220324134031.2648315-1-shraash@google.com>
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From:   Alex Deucher <alexdeucher@gmail.com>
Date:   Fri, 1 Apr 2022 11:28:31 -0400
Message-ID: <CADnq5_NTkB3xrZnT44pCBXercCT7225V2Ui5XTKsY4H45EcXrA@mail.gmail.com>
Subject: Re: [PATCH v2] drm/amd/display: Fix unused-but-set-variable warning
To:     Aashish Sharma <shraash@google.com>
Cc:     Harry Wentland <harry.wentland@amd.com>,
        Leo Li <sunpeng.li@amd.com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Pan Xinhui <Xinhui.Pan@amd.com>,
        David Airlie <airlied@linux.ie>,
        Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>,
        Meenakshikumar Somasundaram <meenakshikumar.somasundaram@amd.com>,
        Jake Wang <haonan.wang2@amd.com>,
        Anson Jacob <Anson.Jacob@amd.com>,
        Guenter Roeck <groeck@chromium.org>,
        kernel test robot <lkp@intel.com>,
        LKML <linux-kernel@vger.kernel.org>,
        Maling list - DRI developers 
        <dri-devel@lists.freedesktop.org>,
        amd-gfx list <amd-gfx@lists.freedesktop.org>,
        Daniel Vetter <daniel@ffwll.ch>, Wayne Lin <wayne.lin@amd.com>,
        Anthony Koo <Anthony.Koo@amd.com>
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Applied.  Thanks!

Alex

On Thu, Mar 24, 2022 at 9:46 AM Aashish Sharma <shraash@google.com> wrote:
>
> Fix the kernel test robot warning below:
>
> drivers/gpu/drm/amd/amdgpu/../display/dmub/inc/dmub_cmd.h:2893:12:
> warning: variable 'temp' set but not used [-Wunused-but-set-variable]
>
> Replaced the assignment to the unused temp variable with READ_ONCE()
> macro to flush the writes. READ_ONCE() helps avoid the use of
> volatile and makes it obvious from the code that the read here is
> intentional. Also verified on x86 that the generated code is exactly the
> same as before.
>
> Reported-by: kernel test robot <lkp@intel.com>
> Signed-off-by: Aashish Sharma <shraash@google.com>
> ---
> v2: Removed unnecessary volatile qualifier in the typecast and an unnecessary comment. Also reworded the commit message.
> ---
>  drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h b/drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h
> index 873ecd04e01d..a58f460f431d 100644
> --- a/drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h
> +++ b/drivers/gpu/drm/amd/display/dmub/inc/dmub_cmd.h
> @@ -2913,13 +2913,11 @@ static inline void dmub_rb_flush_pending(const struct dmub_rb *rb)
>         uint32_t wptr = rb->wrpt;
>
>         while (rptr != wptr) {
> -               uint64_t volatile *data = (uint64_t volatile *)((uint8_t *)(rb->base_address) + rptr);
> -               //uint64_t volatile *p = (uint64_t volatile *)data;
> -               uint64_t temp;
> +               uint64_t *data = (uint64_t *)((uint8_t *)(rb->base_address) + rptr);
>                 uint8_t i;
>
>                 for (i = 0; i < DMUB_RB_CMD_SIZE / sizeof(uint64_t); i++)
> -                       temp = *data++;
> +                       (void)READ_ONCE(*data++);
>
>                 rptr += DMUB_RB_CMD_SIZE;
>                 if (rptr >= rb->capacity)
> --
> 2.35.1.894.gb6a874cedc-goog
>