linux-kernel - Re: [PATCH v2 1/2] drm/panel: jd9365da: Modify Kingdisplay and Melfas panel timing

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Message-ID: <CA+6=WdTTwXSyqGFGM6mqG3djDBH28mAzBUxUEUdr6z7W2g-A7A@mail.gmail.com>
Date: Tue, 24 Sep 2024 10:13:55 +0800
From: zhaoxiong lv <lvzhaoxiong@...qin.corp-partner.google.com>
To: Jessica Zhang <quic_jesszhan@...cinc.com>
Cc: neil.armstrong@...aro.org, sam@...nborg.org, 
	maarten.lankhorst@...ux.intel.com, mripard@...nel.org, tzimmermann@...e.de, 
	airlied@...il.com, simona@...ll.ch, dianders@...omium.org, hsinyi@...gle.com, 
	awarnecke002@...mail.com, dmitry.baryshkov@...aro.org, 
	dri-devel@...ts.freedesktop.org, devicetree@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] drm/panel: jd9365da: Modify Kingdisplay and Melfas
 panel timing

On Tue, Sep 24, 2024 at 5:14 AM Jessica Zhang <quic_jesszhan@...cinc.com> wrote:
>
>
>
> On 9/23/2024 6:42 AM, Zhaoxiong Lv wrote:
> > In MTK chips, if the system starts suspending before the DRM runtime
> > resume has not completed, there is a possibility of a black screen
> > after waking the machine. Reduce the disable delay resolves this issue,
>
> Hi Zhaoxiong,
>
> Do you mean "if the system starts suspending before the DRM runtime
> resume *has* completed" here?

Hi Jessica

Sorry, my description may not be clear enough. It should be when the
DRM runtime resume has not yet completed and the system enters sleep
mode at the same time.


>
> >
> > The "backlight_off_to_display_off_delay_ms" was added between
> > "backlight off" and "display off"  to prevent "display off" from being
> > executed when the backlight is not fully powered off, which may cause
> > a white screen. However, we removed this
> > "backlight_off_to_display_off_delay_ms" and found that this situation
> > did not occur. Therefore, in order to solve the problem mentioned
> > above, we We reduced it from 100ms to 3ms (tCMD_OFF >= 1ms).
>
> So from my understanding of this paragraph,
> `backlight_off_to_display_off_delay_ms` was added to prevent the display
> powering off before backlight is fully powered off. You recently tested
> dropping this completely and saw no issue with this.
>
> If that's the case, why not drop this delay completely?
>
> Thanks,
>
> Jessica Zhang

Yes, there are currently no other issue after removing this delay.
The reason why I didn't completely remove this delay is because the
panel spec states that a delay of more than 1ms  (tCMD_OFF >= 1ms) is
required when entering diaplay_off (0x28H), so I reserved 3ms.

>
> >
> > This is the timing specification for the two panels:
> > 1. Kingdisplay panel timing spec:
> > https://github.com/KD54183/-JD9365DA_Power-On-Off-Sequence_V0120240923
> > 2. LMFBX101117480 timing spec: https://github.com/chiohsin-lo/TDY-JD_LIB
> >
> >
> > Fixes: 2b976ad760dc ("drm/panel: jd9365da: Support for kd101ne3-40ti MIPI-DSI panel")
> > Fixes: c4ce398cf18a ("drm/panel: jd9365da: Support for Melfas lmfbx101117480 MIPI-DSI panel")
> >
> > Signed-off-by: Zhaoxiong Lv <lvzhaoxiong@...qin.corp-partner.google.com>
> > ---
> > Changes between V2 and V1:
> > -  1. Modify the commit message
> > -  2. Modify the value of backlight_off_to_display_off_delay_ms.
> > v1: https://lore.kernel.org/all/20240915080830.11318-2-lvzhaoxiong@huaqin.corp-partner.google.com/
> > ---
> >   drivers/gpu/drm/panel/panel-jadard-jd9365da-h3.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/panel/panel-jadard-jd9365da-h3.c b/drivers/gpu/drm/panel/panel-jadard-jd9365da-h3.c
> > index 44897e5218a6..486aa20e5518 100644
> > --- a/drivers/gpu/drm/panel/panel-jadard-jd9365da-h3.c
> > +++ b/drivers/gpu/drm/panel/panel-jadard-jd9365da-h3.c
> > @@ -858,7 +858,7 @@ static const struct jadard_panel_desc kingdisplay_kd101ne3_40ti_desc = {
> >       .reset_before_power_off_vcioo = true,
> >       .vcioo_to_lp11_delay_ms = 5,
> >       .lp11_to_reset_delay_ms = 10,
> > -     .backlight_off_to_display_off_delay_ms = 100,
> > +     .backlight_off_to_display_off_delay_ms = 3,
> >       .display_off_to_enter_sleep_delay_ms = 50,
> >       .enter_sleep_to_reset_down_delay_ms = 100,
> >   };
> > @@ -1109,7 +1109,7 @@ static const struct jadard_panel_desc melfas_lmfbx101117480_desc = {
> >       .reset_before_power_off_vcioo = true,
> >       .vcioo_to_lp11_delay_ms = 5,
> >       .lp11_to_reset_delay_ms = 10,
> > -     .backlight_off_to_display_off_delay_ms = 100,
> > +     .backlight_off_to_display_off_delay_ms = 3,
> >       .display_off_to_enter_sleep_delay_ms = 50,
> >       .enter_sleep_to_reset_down_delay_ms = 100,
> >   };
> > --
> > 2.17.1
> >
>