linux-kernel - Re: [PATCH] media: mtk-vpu: avoid unaligned access to DTCM buffer.

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Date:   Fri, 14 Feb 2020 19:59:30 +0800
From:   Hsin-Yi Wang <hsinyi@...omium.org>
To:     Hans Verkuil <hverkuil-cisco@...all.nl>
Cc:     "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Minghsiu Tsai <minghsiu.tsai@...iatek.com>,
        Houlong Wei <houlong.wei@...iatek.com>,
        Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        Tiffany Lin <tiffany.lin@...iatek.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        linux-media@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] media: mtk-vpu: avoid unaligned access to DTCM buffer.

On Fri, Feb 14, 2020 at 6:52 PM Hans Verkuil <hverkuil-cisco@...all.nl> wrote:
>
> Hi Hsin-Yi Wang,
>
> On 2/10/20 4:53 AM, Hsin-Yi Wang wrote:
> > struct vpu_run *run in vpu_init_ipi_handler() is an ioremapped DTCM (Data
> > Tightly Coupled Memory) buffer shared with AP.  It's not able to do
> > unaligned access. Otherwise kernel would crash due to unable to handle
> > kernel paging request.
> >
> > struct vpu_run {
> >       u32 signaled;
> >       char fw_ver[VPU_FW_VER_LEN];
> >       unsigned int    dec_capability;
> >       unsigned int    enc_capability;
> >       wait_queue_head_t wq;
> > };
> >
> > fw_ver starts at 4 byte boundary. If system enables
> > CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS, strscpy() will do
> > read_word_at_a_time(), which tries to read 8-byte: *(unsigned long *)addr
> >
> > Copy the string by memcpy_fromio() for this buffer to avoid unaligned
> > access.
> >
> > Fixes: 85709cbf1524 ("media: replace strncpy() by strscpy()")
> > Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
>
> This patch results in the following sparse warnings:
>
> sparse: WARNINGS
> SPARSE:mtk-vpu/mtk_vpu.c mtk-vpu/mtk_vpu.c:834:52:  warning: incorrect type in argument 3 (incompatible argument 1 (different address spaces))
> SPARSE:mtk-vpu/mtk_vpu.c mtk-vpu/mtk_vpu.c:609:29:  warning: dereference of noderef expression
> SPARSE:mtk-vpu/mtk_vpu.c mtk-vpu/mtk_vpu.c:613:35:  warning: dereference of noderef expression
> SPARSE:mtk-vpu/mtk_vpu.c mtk-vpu/mtk_vpu.c:614:35:  warning: dereference of noderef expression
>
> Can you take a look?
>
> Regards,
>
>         Hans
>
Thanks, I'll send a v2 to fix this