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

[Dafna Hirschfeld <dafna.hirschfeld@collabora.com>]

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

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