Re: [PATCH v3,4/4] drm/mediatek: Add pull-down MIPI operation in mtk_dsi_poweroff function

[xinlei.lee <xinlei.lee@mediatek.com>]

On Thu, 2022-03-17 at 20:20 +0800, Rex-BC Chen wrote:
> Hello Xinlei,
> 
> On Thu, 2022-03-17 at 15:53 +0800, xinlei.lee@mediatek.com wrote:
> > From: Xinlei Lee <xinlei.lee@mediatek.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@mediatek.com>
> > Signed-off-by: Xinlei Lee <xinlei.lee@mediatek.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);
> >  
> 
> 

Hi rex:

1. 
If you disable dsi without pulling the mipi signal low, the value of
the register will still maintain the setting of the mipi signal being
pulled high. 
After resume, even if the mipi signal is not pulled high, it will still
be in the high state.

2.So set lane num to 0 means pull down mipi
=> yes

Do you have any suggestions on the next version?

Best Regards!
xinlei
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