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

[Dafna Hirschfeld]

On 03.11.21 10:19, Irui Wang wrote:
> Hi,
>
> The "len" of share_buf copied should be always 8 alignment;
> do you have other logs to prove the len is not 8 alignment when errors
> appear?

Hi, I found out that "sizeof(mdp_ipi_comm) = 20"
this is due to the macro #pragma pack(push, 4) in mtk_mdp_ipi.h

see [1]

[1] http://lkml.iu.edu/hypermail/linux/kernel/2109.2/04978.html

Thanks,
Dafna

> > > [58.350841] mtk-mdp 14001000.rdma: processing failed: -22
>
> On Wed, 2021-11-03 at 16:03 +0800, houlong wei wrote:
> > 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@xxxxxxxxx>
> > > > wrote:
> > > > > On 20/09/2021 19:04, Dafna Hirschfeld wrote:
> > > > > > From: Alexandre Courbot <acourbot@xxxxxxxxxxxx>
> > > > > >
> > > > > > 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@xxxxxxxxxxxx>
> > > > > > Signed-off-by: Enric Balletbo i Serra <
> > > > > > enric.balletbo@xxxxxxxxxxxxx>
> > > > > > Signed-off-by: Dafna Hirschfeld <
> > > > > > dafna.hirschfeld@xxxxxxxxxxxxx
> > > > > > >
> > > > > >
> > > > > > Reviewed-by: Houlong Wei <houlong.wei@xxxxxxxxxxxx>
> > > > > > ---
> > > > > > 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.