linux-kernel - Re: [PATCH v4] media: mtk-vpu: Ensure alignment of 8 for DTCM buffer

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Message-ID: <c01c2c6e2351c915fb6e55b025bf2ab5c449f045.camel@mediatek.com>
Date:   Wed, 3 Nov 2021 16:03:28 +0800
From:   houlong wei <houlong.wei@...iatek.com>
To:     <Irui.wang@...iatek.com>,
        Dafna Hirschfeld <dafna.hirschfeld@...labora.com>,
        Alexandre Courbot <acourbot@...omium.org>,
        Hans Verkuil <hverkuil@...all.nl>
CC:     Linux Media Mailing List <linux-media@...r.kernel.org>,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@...ts.infradead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "kernel@...labora.com" <kernel@...labora.com>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Dafna Hirschfeld <dafna3@...il.com>,
        "Tiffany Lin (林慧珊)" 
        <tiffany.lin@...iatek.com>,
        Andrew-CT Chen (陳智迪) 
        <Andrew-CT.Chen@...iatek.com>,
        Minghsiu Tsai (蔡明修) 
        <Minghsiu.Tsai@...iatek.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        <houlong.wei@...iatek.com>
Subject: Re: [PATCH v4] media: mtk-vpu: Ensure alignment of 8 for DTCM buffer

Add mtk-vpu driver expert irui.wang in the loop.

On Mon, 2021-10-18 at 15:07 +0800, Dafna Hirschfeld wrote:
> 
> On 18.10.21 03:16, Alexandre Courbot wrote:
> > Hi Hans!
> > 
> > On Mon, Oct 4, 2021 at 6:37 PM Hans Verkuil <hverkuil@...all.nl>
> > wrote:
> > > 
> > > On 20/09/2021 19:04, Dafna Hirschfeld wrote:
> > > > From: Alexandre Courbot <acourbot@...omium.org>
> > > > 
> > > > When running memcpy_toio:
> > > > memcpy_toio(send_obj->share_buf, buf, len);
> > > > it was found that errors appear if len is not a multiple of 8:
> > > > 
> > > > [58.350841] mtk-mdp 14001000.rdma: processing failed: -22
> > > 
> > > Why do errors appear? Is that due to a HW bug? Some other reason?
> > 
> > MTK folks would be the best placed to answer this, but since the
> > failure is reported by the firmware I'd suspect either a firmware
> > or
> > hardware limitation.
> > 
> > > 
> > > > 
> > > > This patch ensures the copy of a multiple of 8 size by calling
> > > > round_up(len, 8) when copying
> > > > 
> > > > Fixes: e6599adfad30 ("media: mtk-vpu: avoid unaligned access to
> > > > DTCM buffer.")
> > > > Signed-off-by: Alexandre Courbot <acourbot@...omium.org>
> > > > Signed-off-by: Enric Balletbo i Serra <
> > > > enric.balletbo@...labora.com>
> > > > Signed-off-by: Dafna Hirschfeld <dafna.hirschfeld@...labora.com
> > > > >
> > > > Reviewed-by: Houlong Wei <houlong.wei@...iatek.com>
> > > > ---
> > > > changes since v3:
> > > > 1. multile -> multiple
> > > > 2. add inline doc
> > > > 
> > > > changes since v2:
> > > > 1. do the extra copy only if len is not multiple of 8
> > > > 
> > > > changes since v1:
> > > > 1. change sign-off-by tags
> > > > 2. change values to memset
> > > > 
> > > >   drivers/media/platform/mtk-vpu/mtk_vpu.c | 15 ++++++++++++++-
> > > >   1 file changed, 14 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/drivers/media/platform/mtk-vpu/mtk_vpu.c
> > > > b/drivers/media/platform/mtk-vpu/mtk_vpu.c
> > > > index ec290dde59cf..1df031716c8f 100644
> > > > --- a/drivers/media/platform/mtk-vpu/mtk_vpu.c
> > > > +++ b/drivers/media/platform/mtk-vpu/mtk_vpu.c
> > > > @@ -349,7 +349,20 @@ int vpu_ipi_send(struct platform_device
> > > > *pdev,
> > > >                }
> > > >        } while (vpu_cfg_readl(vpu, HOST_TO_VPU));
> > > > 
> > > > -     memcpy_toio(send_obj->share_buf, buf, len);
> > > > +     /*
> > > > +      * when copying data to the vpu hardware, the memcpy_toio
> > > > operation must copy
> > > > +      * a multiple of 8. Otherwise the processing fails
> > > 
> > > Same here: it needs to explain why the processing fails.
> 
> Is writing 'due to hardware or firmware limitation' enough?
> If not, then we should wait for mediatek people's response to explain
> if they know more
> 
> > > 
> > > > +      */
> > > > +     if (len % 8 != 0) {
> > > > +             unsigned char data[SHARE_BUF_SIZE];
> > > 
> > > Wouldn't it be more robust if you say:
> > > 
> > >                  unsigned char data[sizeof(send_obj->share_buf)];
> > 
> > Definitely yes.
> 
> I'll send v5 fixing this
> 
> > 
> > > 
> > > I also think that the SHARE_BUF_SIZE define needs a comment
> > > stating that it must be a
> > > multiple of 8, otherwise unexpected things can happen.
> > > 
> > > You also noticed that the current SHARE_BUF_SIZE define is too
> > > low, but I saw
> > > no patch correcting this. Shouldn't that be fixed as well?
> > 
> > AFAICT the firmware expects this exact size on its end, so I don't
> > believe it can be changed that easily. But maybe someone from MTK
> > can
> > prove me wrong.
> > 
> 
> I looked further and noted that the structs that are larger than
> 'SHARE_BUF_SIZE'
> (venc_ap_ipi_msg_enc_ext venc_ap_ipi_msg_set_param_ext)
> are used by drivers that don't use this vpu api, so actually
> SHARE_BUF_SIZE is
> not too low and as Corurbot worte probably not changeable.
> 
> 
> Thanks,
> Dafna
> 
> > Cheers,
> > Alex.
> >