linux-kernel - Re: [PATCH v4, 3/4] drm/mediatek: keep dsi as LP00 before dcs cmds transfer

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Message-ID: <3c9140fbba123550b5532f9917dae4ef10ed5611.camel@mediatek.com>
Date:   Tue, 12 Apr 2022 15:43:34 +0800
From:   Rex-BC Chen <rex-bc.chen@...iatek.com>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>,
        <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-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <jitao.shi@...iatek.com>,
        <Project_Global_Chrome_Upstream_Group@...iatek.com>
Subject: Re: [PATCH v4, 3/4] drm/mediatek: keep dsi as LP00 before dcs cmds
 transfer

On Mon, 2022-04-11 at 11:07 +0200, AngeloGioacchino Del Regno wrote:
> Il 11/04/22 04:31, xinlei.lee@...iatek.com ha scritto:
> > From: Jitao Shi <jitao.shi@...iatek.com>
> > 
> > To comply with the panel sequence, hold the mipi signal to LP00
> > before the dcs cmds transmission,
> > and pull the mipi signal high from LP00 to LP11 until the start of
> > the dcs cmds transmission.
> > The normal panel timing is :
> > (1) pp1800 DC pull up
> > (2) avdd & avee AC pull high
> > (3) lcm_reset pull high -> pull low -> pull high
> > (4) Pull MIPI signal high (LP11) -> initial code -> send video
> > data(HS mode)
> > The power-off sequence is reversed.
> > If dsi is not in cmd mode, then dsi will pull the mipi signal high
> > in the mtk_output_dsi_enable function.
> > 
> > Fixes: 2dd8075d2185 ("drm/mediatek: mtk_dsi: Use the
> > drm_panel_bridge API")
> > 
> > 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 | 28 +++++++++++++++++++++--
> > -----
> >   1 file changed, 21 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c
> > b/drivers/gpu/drm/mediatek/mtk_dsi.c
> > index cf76c53a1af6..9ad6f08c8bfe 100644
> > --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> > +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> > @@ -203,6 +203,7 @@ struct mtk_dsi {
> >   	struct mtk_phy_timing phy_timing;
> >   	int refcount;
> >   	bool enabled;
> > +	bool lanes_ready;
> >   	u32 irq_data;
> >   	wait_queue_head_t irq_wait_queue;
> >   	const struct mtk_dsi_driver_data *driver_data;
> > @@ -654,13 +655,6 @@ static int mtk_dsi_poweron(struct mtk_dsi
> > *dsi)
> >   	mtk_dsi_config_vdo_timing(dsi);
> >   	mtk_dsi_set_interrupt_enable(dsi);
> >   
> > -	mtk_dsi_rxtx_control(dsi);
> > -	usleep_range(30, 100);
> > -	mtk_dsi_reset_dphy(dsi);
> > -	mtk_dsi_clk_ulp_mode_leave(dsi);
> > -	mtk_dsi_lane0_ulp_mode_leave(dsi);
> > -	mtk_dsi_clk_hs_mode(dsi, 0);
> > -
> >   	return 0;
> >   err_disable_engine_clk:
> >   	clk_disable_unprepare(dsi->engine_clk);
> > @@ -689,6 +683,23 @@ static void mtk_dsi_poweroff(struct mtk_dsi
> > *dsi)
> >   	clk_disable_unprepare(dsi->digital_clk);
> >   
> >   	phy_power_off(dsi->phy);
> > +
> > +	dsi->lanes_ready = false;
> > +}
> > +
> > +static void mtk_dsi_lane_ready(struct mtk_dsi *dsi)
> > +{
> > +	if (!dsi->lanes_ready) {
> > +		dsi->lanes_ready = true;
> > +		mtk_dsi_rxtx_control(dsi);
> > +		usleep_range(30, 100);
> > +		mtk_dsi_reset_dphy(dsi);
> > +		mtk_dsi_clk_ulp_mode_leave(dsi);
> > +		mtk_dsi_lane0_ulp_mode_leave(dsi);
> > +		mtk_dsi_clk_hs_mode(dsi, 0);
> > +		msleep(20);
> 
> This is a very long sleep, which wasn't present before this change.
> Please document the reasons why we need this 20ms sleep with a
> comment
> in the code.
> 
> Regards,
> Angelo
> 
> 

Hello Xinlei,

As Angelo mentioned.
I think you should add this in commit message and driver comments.
(Your reply in v3.)
"The 20ms delay in mtk_dsi_lane_ready() is because dsi needs to give
dsi_rx(panel) a reaction time after pulling up the mipi signal."

BRs,
Rex