Re: [PATCH v17 13/21] drm/mediatek: add display merge async reset control

[Philipp Zabel <p.zabel@pengutronix.de>]

On Sa, 2022-04-16 at 10:07 +0800, Nancy.Lin wrote:
> Add merge async reset control in mtk_merge_stop. Async hw doesn't do self
> reset on each sof signal(start of frame), so need to reset the async to
> clear the hw status for the next merge start.
> 
> Signed-off-by: Nancy.Lin <nancy.lin@mediatek.com>
> Reviewed-by: CK Hu <ck.hu@mediatek.com>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_disp_merge.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_disp_merge.c b/drivers/gpu/drm/mediatek/mtk_disp_merge.c
> index 9dca145cfb71..177473fa8160 100644
> --- a/drivers/gpu/drm/mediatek/mtk_disp_merge.c
> +++ b/drivers/gpu/drm/mediatek/mtk_disp_merge.c
> @@ -8,6 +8,7 @@
>  #include <linux/of_device.h>
>  #include <linux/of_irq.h>
>  #include <linux/platform_device.h>
> +#include <linux/reset.h>
>  #include <linux/soc/mediatek/mtk-cmdq.h>
>  
> 
> 
> 
>  #include "mtk_drm_ddp_comp.h"
> @@ -79,6 +80,9 @@ void mtk_merge_stop(struct device *dev)
>  	struct mtk_disp_merge *priv = dev_get_drvdata(dev);
>  
> 
> 
> 
>  	mtk_merge_stop_cmdq(dev, NULL);
> +
> +	if (priv->async_clk)
> +		device_reset_optional(dev);

To avoid the overhead of looking up the reset control in the device
tree every time, it would be better to request a reset control during
probe using devm_reset_control_get_optional_exclusive(). Here you'd
just call reset_control_reset().

regards
Philipp