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

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

On 10.11.21 05:11, Irui Wang wrote:
> 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.

In such case shouldn't we also make sure that the address of
send_obj->share_buf is 8 aligend before calling memcpy_toio,
and also shouldn't we make the same checks for the memcpy_fromio ?

Thanks,
Dafna

> 
> 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@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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