Date:   Fri, 11 Jun 2021 12:31:39 +0800
From:   Chen-Yu Tsai <wenst@...omium.org>
To:     Eizan Miyamoto <eizan@...omium.org>
Cc:     linux-kernel@...r.kernel.org, houlong.wei@...iatek.com,
        enric.balletbo@...labora.com, yong.wu@...iatek.com,
        chunkuang.hu@...nel.org,
        Andrew-CT Chen <andrew-ct.chen@...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 7/8] media: mtk-mdp: treat rdma@...01000 specially when probing

Hi,

On Fri, Jun 11, 2021 at 12:05 PM Eizan Miyamoto <eizan@...omium.org> wrote:
>
> ... Instead of depending on the presence of a mediatek,vpu property in
> the device node.
>
> This property was originally added to link to the vpu node so that the
> mtk_mdp_core driver could pass the right device to
> vpu_wdt_reg_handler(). However in a previous patch in this series,
> the driver has been modified to search the device tree for that node
> instead.
>
> This property was also used to indicate the primary MDP device, so that
> it can be passed to the V4L2 subsystem as well as register it to be
> used when setting up queues in the open() callback for the filesystem
> device node that is created. In this case, assuming that the primary
> MDP device is the one with a specific name at a specific address seems
> useable because the alternative is to add a property to the device tree
> which doesn't actually represent any facet of hardware (i.e., this
> being the primary MDP device is a software decision). In other words,
> this solution is equally as arbitrary, but doesn't add a property to
> a device node which is unrelated to the hardware present.
>
> Signed-off-by: Eizan Miyamoto <eizan@...omium.org>
> ---
>
> (no changes since v1)
>
>  drivers/media/platform/mtk-mdp/mtk_mdp_comp.c | 15 ++++-----------
>  drivers/media/platform/mtk-mdp/mtk_mdp_core.c |  6 ++++++
>  2 files changed, 10 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/media/platform/mtk-mdp/mtk_mdp_comp.c b/drivers/media/platform/mtk-mdp/mtk_mdp_comp.c
> index 59911ee063c1..77ddc18c90e2 100644
> --- a/drivers/media/platform/mtk-mdp/mtk_mdp_comp.c
> +++ b/drivers/media/platform/mtk-mdp/mtk_mdp_comp.c
> @@ -146,17 +146,11 @@ static int mtk_mdp_comp_bind(struct device *dev, struct device *master,
>  {
>         struct mtk_mdp_comp *comp = dev_get_drvdata(dev);
>         struct mtk_mdp_dev *mdp = data;
> -       struct device_node *vpu_node;
>
>         mtk_mdp_register_component(mdp, comp);
>
> -       /*
> -        * If this component has a "mediatek-vpu" property, it is responsible for
> -        * notifying the mdp master driver about it so it can be further initialized
> -        * later.
> -        */
> -       vpu_node = of_parse_phandle(dev->of_node, "mediatek,vpu", 0);
> -       if (vpu_node) {
> +       if (strcmp(dev->of_node->full_name, "rdma@...01000") == 0) {
> +               /* This is the primary MDP device node. */

This seems quite fragile as it likely doesn't hold true across different SoCs.
You would then end up with a bunch of of_device_is_compatible() and
name checking
combinations.

Would it make more sense to check against DT aliases? Since this
device already has
the mdp-rdma0 alias associated with it, we could mandate some alias
naming scheme
going forward?


ChenYu

>                 int ret;
>
>                 ret = v4l2_device_register(dev, &mdp->v4l2_dev);
> @@ -172,9 +166,8 @@ static int mtk_mdp_comp_bind(struct device *dev, struct device *master,
>                 }
>
>                 /*
> -                * presence of the "mediatek,vpu" property in a device node
> -                * indicates that it is the primary MDP rdma device and MDP DMA
> -                * ops should be handled by its DMA callbacks.
> +                * MDP DMA ops will be handled by the DMA callbacks associated with this
> +                * device;
>                  */
>                 mdp->rdma_dev = dev;
>         }
> diff --git a/drivers/media/platform/mtk-mdp/mtk_mdp_core.c b/drivers/media/platform/mtk-mdp/mtk_mdp_core.c
> index 523e3c2798e1..be7d35b3e3ff 100644
> --- a/drivers/media/platform/mtk-mdp/mtk_mdp_core.c
> +++ b/drivers/media/platform/mtk-mdp/mtk_mdp_core.c
> @@ -157,6 +157,12 @@ static int mtk_mdp_master_bind(struct device *dev)
>                 goto err_component_bind_all;
>         }
>
> +       if (mdp->rdma_dev == NULL) {
> +               dev_err(dev, "Primary MDP device not found");
> +               status = -ENODEV;
> +               goto err_component_bind_all;
> +       }
> +
>         vpu_node = of_find_node_by_name(NULL, "vpu");
>         if (!vpu_node) {
>                 dev_err(dev, "unable to finddrivers/soc/mediatek/mtk-mmsys.c vpu node");
> --
> 2.32.0.272.g935e593368-goog
>
>
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