linux-kernel - Re: [PATCH v3,4/4] drm/mediatek: Add pull-down MIPI operation in mtk_dsi

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Date:   Thu, 17 Mar 2022 20:20:16 +0800
From:   Rex-BC Chen <rex-bc.chen@...iatek.com>
To:     <xinlei.lee@...iatek.com>, <chunkuang.hu@...nel.org>,
        <p.zabel@...gutronix.de>, <airlied@...ux.ie>, <daniel@...ll.ch>,
        <matthias.bgg@...il.com>
CC:     <dri-devel@...ts.freedesktop.org>,
        <linux-mediatek@...ts.infradead.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>,
        <Project_Global_Chrome_Upstream_Group@...iatek.com>,
        <jitao.shi@...iatek.com>
Subject: Re: [PATCH v3,4/4] drm/mediatek: Add pull-down MIPI operation in
 mtk_dsi_poweroff function

Hello Xinlei,

On Thu, 2022-03-17 at 15:53 +0800, xinlei.lee@...iatek.com wrote:
> From: Xinlei Lee <xinlei.lee@...iatek.com>
> 
> In the dsi_enable function, mtk_dsi_rxtx_control is to
> pull up the MIPI signal operation. Before dsi_disable,
> MIPI should also be pulled down by writing a register instead of
> disabling dsi.
> 

What will happen if you do not pulled down the mipi before disable dsi?
What's differnet for this two setting?

> Signed-off-by: Jitao Shi <jitao.shi@...iatek.com>
> Signed-off-by: Xinlei Lee <xinlei.lee@...iatek.com>
> ---
>  drivers/gpu/drm/mediatek/mtk_dsi.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c
> b/drivers/gpu/drm/mediatek/mtk_dsi.c
> index b509d59235e2..1c6a75a46b67 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> @@ -676,6 +676,8 @@ static void mtk_dsi_poweroff(struct mtk_dsi *dsi)
>  	mtk_dsi_reset_engine(dsi);
>  	mtk_dsi_lane0_ulp_mode_enter(dsi);
>  	mtk_dsi_clk_ulp_mode_enter(dsi);
> +	/* set the lane number as 0 */
> +	writel(0, dsi->regs + DSI_TXRX_CTRL);

So set lane num to 0 means pull down mipi?

BRs,
Rex

>  
>  	mtk_dsi_disable(dsi);
>