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

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Message-ID: <b4f438026fe208f8f6511de34c7e84c8c59d843c.camel@pengutronix.de>
Date:   Mon, 25 Apr 2022 11:58:04 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     "Nancy.Lin" <nancy.lin@...iatek.com>,
        Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        wim@...ux-watchdog.org,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, linux@...ck-us.net
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Nathan Chancellor <nathan@...nel.org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        "jason-jh . lin" <jason-jh.lin@...iatek.com>,
        Yongqiang Niu <yongqiang.niu@...iatek.com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        dri-devel@...ts.freedesktop.org, llvm@...ts.linux.dev,
        singo.chang@...iatek.com, srv_heupstream@...iatek.com,
        Project_Global_Chrome_Upstream_Group@...iatek.com
Subject: Re: [PATCH v17 13/21] drm/mediatek: add display merge async reset
 control

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@...iatek.com>
> Reviewed-by: CK Hu <ck.hu@...iatek.com>
> Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.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