linux-kernel - Re: [PATCH v2] media: mediatek: vcodec: fix h264 cavlc bitstream fail

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Date:   Tue, 15 Nov 2022 09:48:38 +0100
From:   AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
To:     Yunfei Dong (董云飞) 
        <Yunfei.Dong@...iatek.com>,
        "wenst@...omium.org" <wenst@...omium.org>,
        Tiffany Lin (林慧珊) 
        <tiffany.lin@...iatek.com>,
        "nicolas@...fresne.ca" <nicolas@...fresne.ca>,
        "benjamin.gaignard@...labora.com" <benjamin.gaignard@...labora.com>,
        "hverkuil-cisco@...all.nl" <hverkuil-cisco@...all.nl>
Cc:     Xiaoyong Lu (卢小勇) 
        <Xiaoyong.Lu@...iatek.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        George Sun (孙林) <George.Sun@...iatek.com>,
        "frkoenig@...omium.org" <frkoenig@...omium.org>,
        "stevecho@...omium.org" <stevecho@...omium.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "mchehab@...nel.org" <mchehab@...nel.org>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        Project_Global_Chrome_Upstream_Group 
        <Project_Global_Chrome_Upstream_Group@...iatek.com>,
        "hsinyi@...omium.org" <hsinyi@...omium.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "matthias.bgg@...il.com" <matthias.bgg@...il.com>
Subject: Re: [PATCH v2] media: mediatek: vcodec: fix h264 cavlc bitstream fail

Il 15/11/22 03:00, Yunfei Dong (董云飞) ha scritto:
> Hi AngeloGioacchino,
> 
> Thanks for your detail suggestion.
> On Mon, 2022-11-14 at 12:08 +0100, AngeloGioacchino Del Regno wrote:
>> Il 18/10/22 13:41, Yunfei Dong ha scritto:
>>> Some cavlc bistream will decode fail when the frame size is small
>>> than
>>
>> s/small/smaller/g
> 
> Will fix in next patch.
>>
>>> 20 bytes. Need to add pending data at the end of the bitstream.
>>>
>>> For the minimum size of mapped memory is 256 bytes(16x16), adding
>>> four bytes data
>>> won't lead to access unknown virtual memory.
>>>
>>> Fixes: 59fba9eed5a7 ("media: mediatek: vcodec: support stateless
>>> H.264 decoding for mt8192")
>>> Signed-off-by: Yunfei Dong <yunfei.dong@...iatek.com>
>>> ---
>>> compared with v1:
>>> - add detail comments for function: vdec_h264_insert_startcode.
>>> - re-write commit message.
>>> ---
>>>    .../vcodec/vdec/vdec_h264_req_multi_if.c      | 32
>>> +++++++++++++++++--
>>>    1 file changed, 29 insertions(+), 3 deletions(-)
>>>
>>> diff --git
>>> a/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_i
>>> f.c
>>> b/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_i
>>> f.c
>>> index 4cc92700692b..18e048755d11 100644
>>> ---
>>> a/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_i
>>> f.c
>>> +++
>>> b/drivers/media/platform/mediatek/vcodec/vdec/vdec_h264_req_multi_i
>>> f.c
>>> @@ -539,6 +539,29 @@ static int vdec_h264_slice_core_decode(struct
>>> vdec_lat_buf *lat_buf)
>>>    	return 0;
>>>    }
>>>    
>>> +static void vdec_h264_insert_startcode(struct mtk_vcodec_dev
>>> *vcodec_dev, unsigned char *buf,
>>> +				       size_t *bs_size, struct
>>> mtk_h264_pps_param *pps)
>>> +{
>>> +	struct device *dev = &vcodec_dev->plat_dev->dev;
>>> +
>>> +	/* Need to add pending data at the end of bitstream when bs_sz
>>> is small than
>>> +	 * 20 bytes for cavlc bitstream, or lat will decode fail. This
>>> pending data is
>>> +	 * useful for mt8192 and mt8195 platform.
>>
>> What is the reason why other SoCs don't need this?
>>
> For the hardware not add this feature, and will add in the future Soc.
>>> +	 *
>>> +	 * cavlc bitstream when entropy_coding_mode_flag is false.
>>> +	 */
>>> +	if (pps->entropy_coding_mode_flag || *bs_size > 20 ||
>>> +	    !(of_device_is_compatible(dev->of_node, "mediatek,mt8192-
>>> vcodec-dec") ||
>>> +	    of_device_is_compatible(dev->of_node, "mediatek,mt8195-
>>> vcodec-dec")))
>>
>> I'm not comfortable seeing of_device_is_compatible... this list will
>> grow whenever
>> a new SoC needing this appears.
>> Please think about a good name for a flag/quirk, or a bool, in the
>> platform data
>> for these two SoCs and use it.
>>
> For this feature only need to add in these two Socs, and won't grow
> anymore. So just want to use compatible to separate, not add one flags.
> 
> So you think that using one flag to separate much better?
> 

A flag is better: please remember that calls to of_device_is_compatible()
will perform a string comparison which, as you know, as much optimized as
it can be, it's always going to be slower than a simple integer/bool/flag
check.

This means that even for functional (not just cosmetic) reasons we should
not use of_device_is_compatible() here :-)

Cheers,
Angelo