Re: [PATCH] drm/panel: Add prepare_prev_first flag to Visionox VTDR6130

[Abhinav Kumar]

Hi Neil

On 8/3/2023 10:19 AM, Jessica Zhang wrote:
> On 7/31/2023 6:00 AM, Neil Armstrong wrote:
> > Hi,
> >
> > On 26/07/2023 00:56, Jessica Zhang wrote:
> > > Due to a recent introduction of the pre_enable_prev_first bridge flag 
> > > [1],
> > > the panel driver will be probed before the DSI is enabled, causing the
> > > DCS commands to fail to send.
> > >
> > > Ensure that DSI is enabled before panel probe by setting the
> > > prepare_prev_first flag for the panel.
> >
> > Well this is specific to MSM DSI driver, it's not related at all to 
> > the panel.

I dont fully agree this is a MSM DSI driver specific thing.

If the panel can send its commands in its enable() callback, then this 
flag need not be set.

When a panel sends its DCS commands in its pre_enable() callback, any 
DSI controller will need to be ON before that otherwise DCS commands 
cannot be sent.

With this in mind, may I know why is this a MSM change and not a panel 
change?

As per my discussion with Dmitry during the last sync up, we were 
aligned on this expectation.

Thanks

Abhinav

> Hi Neil,
>
> I think there might be some confusion caused by the commit message -- 
> instead of "enabled before panel probe", it should be "enabled before 
> panel pre_enable()" as the panel on commands are sent during prepare(), 
> which is matched to bridge pre_enable().
>
> IIRC the general rule is that the panel driver should set the 
> prepare_prev_first flag if the on commands are sent during pre_enable(), 
> so I'll keep the code change but correct the commit message if that's ok 
> with you.
>
> Thanks,

> Jessica Zhang
>
> > Neil
> >
> > > [1] commit 4fb912e5e190 ("drm/bridge: Introduce pre_enable_prev_first 
> > > to alter bridge init order")
> > >
> > > Fixes: 2349183d32d8 ("drm/panel: add visionox vtdr6130 DSI panel 
> > > driver")
> > > Signed-off-by: Jessica Zhang <quic_jesszhan@xxxxxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/panel/panel-visionox-vtdr6130.c | 1 +
> > >   1 file changed, 1 insertion(+)
> > >
> > > diff --git a/drivers/gpu/drm/panel/panel-visionox-vtdr6130.c 
> > > b/drivers/gpu/drm/panel/panel-visionox-vtdr6130.c
> > > index bb0dfd86ea67..e1363e128e7e 100644
> > > --- a/drivers/gpu/drm/panel/panel-visionox-vtdr6130.c
> > > +++ b/drivers/gpu/drm/panel/panel-visionox-vtdr6130.c
> > > @@ -296,6 +296,7 @@ static int visionox_vtdr6130_probe(struct 
> > > mipi_dsi_device *dsi)
> > >       dsi->format = MIPI_DSI_FMT_RGB888;
> > >       dsi->mode_flags = MIPI_DSI_MODE_VIDEO | 
> > > MIPI_DSI_MODE_NO_EOT_PACKET |
> > >                 MIPI_DSI_CLOCK_NON_CONTINUOUS;
> > > +    ctx->panel.prepare_prev_first = true;
> > >       drm_panel_init(&ctx->panel, dev, &visionox_vtdr6130_panel_funcs,
> > >                  DRM_MODE_CONNECTOR_DSI);
> > >
> > > ---
> > > base-commit: 28a5c036b05fc5c935cc72d76abd3589825ea9cd
> > > change-id: 20230717-visionox-vtdr-prev-first-e00ae02eec9f
> > >
> > > Best regards,