Re: [PATCH v9 03/14] drm/mediatek: Add DSI sub driver

[Philipp Zabel <p.zabel@pengutronix.de>]

Am Donnerstag, den 04.02.2016, 14:37 +0800 schrieb CK Hu:
> Hi Philipp:
> 
> On Wed, 2016-02-03 at 12:01 +0100, Philipp Zabel wrote:
> > Hi Daniel,
> > 
> 
> > > > +static void mtk_output_dsi_disable(struct mtk_dsi *dsi)
> > > > +{
> > > > +       if (!dsi->enabled)
> > > > +               return;
> > > > +
> > > > +       if (dsi->panel) {
> > > > +               if (drm_panel_disable(dsi->panel)) {
> > > > +                       DRM_ERROR("failed to disable the panel\n");
> > > > +                       return;
> > > > +               }
> > > > +       }
> > > > +
> > > > +       mtk_dsi_poweroff(dsi);
> > > 
> > > The order is a bit suspicious here; I would expect to poweroff dsi
> > > before the panel to mirror the turn on order.
> > 
> > CK, could you comment on this?
> > 
> 
> According to the experience of other Mediatek SoC,
> In mtk_output_dsi_enable(), we should do power on dsi first and then
> prepare panel because dsi should be ready to receive panel prepare error
> message. So we should disable panel and then power off dsi in
> mtk_output_dsi_disable().
> 
> > I can reorder this, but I'm not sure about the reasoning (what happens
> > hardware wise if we just cut panel power vs. if the DSI panel first sees
> > the ULP transition). Further, I don't have a panel to test, just the
> > PS8640.
> > 
> > thanks
> > Philipp

I just realized that this code isn't even using drm_panel_enable and
drm_panel_unprepare. I suppose the order generally should be:

prepare and enable dsi (but don't start stream yet)
drm_panel_prepare()
enable dsi output
drm_panel_enable()

and to disable:

drm_panel_disable()
disable dsi output
drm_panel_unprepare()
power off dsi

?

regards
Philipp

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