Re: [PATCH v7 2/7] mtk-mdp: add driver to probe mdp components

From: Hans Verkuil <hverkuil@xs4all.nl>
To: Ezequiel Garcia <ezequiel@vanguardiasur.com.ar>
Cc: "houlong wei" <houlong.wei@mediatek.com>,
	"Eizan Miyamoto" <eizan@chromium.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"chunkuang.hu@kernel.org" <chunkuang.hu@kernel.org>,
	"Yong Wu (吴勇)" <Yong.Wu@mediatek.com>,
	"wenst@chromium.org" <wenst@chromium.org>,
	"CK Hu (胡俊光)" <ck.hu@mediatek.com>,
	"Enric Balletbo i Serra" <enric.balletbo@collabora.com>,
	"Yongqiang Niu (牛永强)" <yongqiang.niu@mediatek.com>,
	"Andrew-CT Chen (陳智迪)" <Andrew-CT.Chen@mediatek.com>,
	"Matthias Brugger" <matthias.bgg@gmail.com>,
	"Mauro Carvalho Chehab" <mchehab@kernel.org>,
	"Minghsiu Tsai (蔡明修)" <Minghsiu.Tsai@mediatek.com>,
	linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
	linux-media <linux-media@vger.kernel.org>,
	"moderated list:ARM/Mediatek SoC support"
	<linux-mediatek@lists.infradead.org>
Subject: Re: [PATCH v7 2/7] mtk-mdp: add driver to probe mdp components
Date: Tue, 7 Dec 2021 14:02:06 +0100	[thread overview]
Message-ID: <ed43d910-d293-fb27-39fe-119836672738@xs4all.nl> (raw)
In-Reply-To: <CAAEAJfDOU+tCjm=B8Mg0esZf=e99MM1cv+8SUN6sCBKq0hVvZw@mail.gmail.com>

On 12/7/21 1:46 PM, Ezequiel Garcia wrote:
> Hi everyone,
> 
> On Tue, 7 Dec 2021 at 09:37, Hans Verkuil <hverkuil@xs4all.nl> wrote:
>>
>> On 9/5/21 6:23 PM, houlong wei wrote:
>>> Hi Ezequiel,
>>>
>>> Thank you for your attention to this series of patches. I answer partial of your questions below.
>>> Regards,
>>> Houlong
>>>
>>> On Sat, 2021-09-04 at 20:34 +0800, Ezequiel Garcia wrote:
>>>> Hi Eizan,
>>>>
>>>> Sorry for seeing this series so late.
>>>>
>>>> On Wed, 25 Aug 2021 at 03:35, Eizan Miyamoto <eizan@chromium.org>
>>>> wrote:
>>>>>
>>>>> Broadly, this patch (1) adds a driver for various MTK MDP
>>>>> components to
>>>>> go alongside the main MTK MDP driver, and (2) hooks them all
>>>>> together
>>>>> using the component framework.
>>>>>
>>>>> (1) Up until now, the MTK MDP driver controls 8 devices in the
>>>>> device
>>>>> tree on its own. When running tests for the hardware video decoder,
>>>>> we
>>>>> found that the iommus and LARBs were not being properly configured.
>>>>
>>>> Why were not being properly configured? What was the problem?
>>>> Why not fixing that instead?
>>>>
>>>> Does this mean the driver is currently broken and unusable?
>>>
>>> This series of patches are supplements to another series, please refer
>>> to
>>> https://patchwork.kernel.org/project/linux-mediatek/list/?series=515129c
>>> , which add device link between the mtk-iommu consumer and the mtk-larb
>>> devices. Without that series of patches, the mtk-mdp driver can work
>>> well so far.
>>> But with that series, it seems the device link only can be established
>>> for the device which is registered as a platform driver. That's why
>>> Eizan adds this series of patches to make all mdp components to be
>>> registered as platform drivers.
>>
>> Hold on, so this means that if that iommu device-link series is merged,
>> then the mtk-mdp driver breaks? I posted a PR for that iommu series, but
>> I've just withdrawn that PR until this issue is clarified.
>>
>> Is it only mtk-mdp that is affected by this iommu device-link series, or
>> others as well?
>>
> 
> Like I said before, I think it's a mistake to introduce the component
> framework in V4L2. This whole idea looks like a hack to me.
> 
> If we merge this, then we validate using the component framework
> as a way to avoid fixing things properly.

I agree with Ezequiel.

	Hans