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

Tue Nov 9 19:11:30 PST 2021

Hi, Dafna,

Thanks for the patch.
On Tue, 2021-11-09 at 10:46 +0200, Dafna Hirschfeld wrote:
> 
> On 03.11.21 13:04, Dafna Hirschfeld wrote:
> > 
> > 
> > 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
> > 
> 
> Hi Irui Wang,
> Any update regarding that patch?
> Can you give more explanation for that errors that we see
> when the buffer size is not a multiple of 8?
> 
> Thanks,
> Dafna

share_buf is a mapped memory by ioremap, it should be better use
memcpy_to/fromio instead of memcpy because of alignment.

As for memcpy_toio, it may also have requirements for alignment, we can
also get such information from:

https://elixir.bootlin.com/linux/v5.15/source/drivers/mtd/spi-nor/controllers/aspeed-smc.c#L207
.

So, it's not VPU HW bug or limitation, it's memcpy_toio requirements,
maybe we can modify IPI message to do alignment, but it need modify
both kernel and vpu firmware, which will break upstream backward
compatible, we think it's unacceptale.

If this patch can solve the issue, we think it's OK.

Thanks
> 
> > 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 at xs4all.nl>
> > > > > > wrote:
> > > > > > > 
> > > > > > > On 20/09/2021 19:04, Dafna Hirschfeld wrote:
> > > > > > > > From: Alexandre Courbot <acourbot at chromium.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 at chromium.org
> > > > > > > > >
> > > > > > > > Signed-off-by: Enric Balletbo i Serra <
> > > > > > > > enric.balletbo at collabora.com>
> > > > > > > > Signed-off-by: Dafna Hirschfeld <
> > > > > > > > dafna.hirschfeld at collabora.com
> > > > > > > > > 
> > > > > > > > 
> > > > > > > > Reviewed-by: Houlong Wei <houlong.wei at mediatek.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.
> > > > > > 
> > > > 
> > > > 