Re: [PATCH v3 3/3] media: mtk-mdp: Fix mdp device tree

[Matthias Brugger <matthias.bgg@gmail.com>]

On 12/05/17 05:22, Minghsiu Tsai wrote:
> From: Daniel Kurtz <djkurtz@chromium.org>
> 
> If the mdp_* nodes are under an mdp sub-node, their corresponding
> platform device does not automatically get its iommu assigned properly.
> 
> Fix this by moving the mdp component nodes up a level such that they are
> siblings of mdp and all other SoC subsystems.  This also simplifies the
> device tree.
> 
> Although it fixes iommu assignment issue, it also break compatibility
> with old device tree. So, the patch in driver is needed to iterate over
> sibling mdp device nodes, not child ones, to keep driver work properly.
> 

Couldn't we preserve backwards compatibility by doing something like this:
diff --git a/drivers/media/platform/mtk-mdp/mtk_mdp_core.c 
b/drivers/media/platform/mtk-mdp/mtk_mdp_core.c
index 9e4eb7dcc424..277d8fe6eb76 100644
--- a/drivers/media/platform/mtk-mdp/mtk_mdp_core.c
+++ b/drivers/media/platform/mtk-mdp/mtk_mdp_core.c
@@ -103,7 +103,7 @@ static int mtk_mdp_probe(struct platform_device *pdev)
  {
  	struct mtk_mdp_dev *mdp;
  	struct device *dev = &pdev->dev;
-	struct device_node *node;
+	struct device_node *node, *parent;
  	int i, ret = 0;

  	mdp = devm_kzalloc(dev, sizeof(*mdp), GFP_KERNEL);
@@ -117,8 +117,14 @@ static int mtk_mdp_probe(struct platform_device *pdev)
  	mutex_init(&mdp->lock);
  	mutex_init(&mdp->vpulock);

+	/* Old dts had the components as child nodes */
+	if (of_get_next_child(dev->of_node, NULL))
+		parent = dev->of_node;
+	else
+		parent = dev->of_node->parent;
+
  	/* Iterate over sibling MDP function blocks */
-	for_each_child_of_node(dev->of_node, node) {
+	for_each_child_of_node(parent, node) {
  		const struct of_device_id *of_id;
  		enum mtk_mdp_comp_type comp_type;
  		int comp_id;

Maybe even by putting a warning in the if branch to make sure, people 
are aware of their out-of-date device tree blobs.

Regards,
Matthias

> Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
> Signed-off-by: Minghsiu Tsai <minghsiu.tsai@mediatek.com>
> 
> ---
>   drivers/media/platform/mtk-mdp/mtk_mdp_core.c | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/media/platform/mtk-mdp/mtk_mdp_core.c b/drivers/media/platform/mtk-mdp/mtk_mdp_core.c
> index 9e4eb7d..a5ad586 100644
> --- a/drivers/media/platform/mtk-mdp/mtk_mdp_core.c
> +++ b/drivers/media/platform/mtk-mdp/mtk_mdp_core.c
> @@ -118,7 +118,7 @@ static int mtk_mdp_probe(struct platform_device *pdev)
>   	mutex_init(&mdp->vpulock);
>   
>   	/* Iterate over sibling MDP function blocks */
> -	for_each_child_of_node(dev->of_node, node) {
> +	for_each_child_of_node(dev->of_node->parent, node) {
>   		const struct of_device_id *of_id;
>   		enum mtk_mdp_comp_type comp_type;
>   		int comp_id;
>