linux-kernel - Re: [PATCH v2 0/2] Refactor MDP driver and add dummy component driver

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Date:   Fri, 26 Jun 2020 11:37:31 +0200
From:   Enric Balletbo i Serra <enric.balletbo@...labora.com>
To:     Hans Verkuil <hverkuil@...all.nl>,
        Eizan Miyamoto <eizan@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>
Cc:     Andrew-CT Chen <andrew-ct.chen@...iatek.com>,
        Houlong Wei <houlong.wei@...iatek.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Minghsiu Tsai <minghsiu.tsai@...iatek.com>,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH v2 0/2] Refactor MDP driver and add dummy component driver

Hi Eizan and Hans,

On 24/6/20 16:05, Hans Verkuil wrote:
> On 06/05/2020 10:40, Eizan Miyamoto wrote:
>>
>> This series depends on all changes in the series:
>> https://patchwork.kernel.org/patch/11530275/
> 
> I plan on merging the v3 of this series.
> 
>>
>> We are adding a dummy MDP component driver so that all the components
>> are properly configured with IOMMUs and LARBs. This is required for
>> us to get hardware video decode working in 4.19, and possibly newer
>> kernels.
> 
> What is the status of this series?
> 

First of all, sorry, I should have had answer before but for some reason I
missed the track of this patchset.

> There was some discussion with Enric, but that didn't come to a conclusion,
> I think.
> 

Yes, my main concern is how this driver is instantiated, it is using one of the
rdma nodes, see the rdma0 node vs rdma1, to instantiate the driver,

       mdp_rdma0: rdma@...01000 {
                compatible = "mediatek,mt8173-mdp-rdma";
                             "mediatek,mt8173-mdp";
                reg = <0 0x14001000 0 0x1000>;
                clocks = <&mmsys CLK_MM_MDP_RDMA0>,
                         <&mmsys CLK_MM_MUTEX_32K>;
                power-domains = <&scpsys MT8173_POWER_DOMAIN_MM>;
                iommus = <&iommu M4U_PORT_MDP_RDMA0>;
                mediatek,larb = <&larb0>;
                mediatek,vpu = <&vpu>;
        };


        mdp_rdma1: rdma@...02000 {

                compatible = "mediatek,mt8173-mdp-rdma";
                reg = <0 0x14002000 0 0x1000>;
                clocks = <&mmsys CLK_MM_MDP_RDMA1>,
                         <&mmsys CLK_MM_MUTEX_32K>;
                power-domains = <&scpsys MT8173_POWER_DOMAIN_MM>;
                iommus = <&iommu M4U_PORT_MDP_RDMA1>;
                mediatek,larb = <&larb4>;
        };


My point is that DT is to describe hardware not a trick to instantiate drivers,
so the "mediatek,mt8173-mdp" is completely unnecessary. We had the same issue
with the MMSYS driver and the mediatek DRM driver, and we solved by having the
mmsys driver instantiating the drm driver. I think we should apply the same
solution here, see [1] for reference. If you want to continue the discussion
maybe would be better


Thanks,
 Enric

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/soc/mediatek/mtk-mmsys.c?id=667c769246b01c53ad0925d603d2a2531abd3ef2

> Regards,
> 
> 	Hans
> 
>>
>> Changes in v2:
>> - remove empty mtk_mdp_comp_init
>> - update documentation for enum mtk_mdp_comp_type
>> - remove comma after last element of mtk_mdp_comp_driver_dt_match
>>
>> Eizan Miyamoto (2):
>>   [media] mtk-mdp: add driver to probe mdp components
>>   [media] mtk-mdp: use pm_runtime in MDP component driver
>>
>>  drivers/media/platform/mtk-mdp/mtk_mdp_comp.c | 172 ++++++++++++++---
>>  drivers/media/platform/mtk-mdp/mtk_mdp_comp.h |  32 +--
>>  drivers/media/platform/mtk-mdp/mtk_mdp_core.c | 182 ++++++++++++------
>>  drivers/media/platform/mtk-mdp/mtk_mdp_core.h |   1 +
>>  4 files changed, 286 insertions(+), 101 deletions(-)
>>
>