Re: [PATCH v5 3/7] drm: sun4i: dsi: Convert to bridge driver

[Jagan Teki <jagan@amarulasolutions.com>]

Hi Neil,

On Mon, Nov 22, 2021 at 6:22 PM Neil Armstrong <narmstrong@baylibre.com> wrote:
>
> On 22/11/2021 07:52, Jagan Teki wrote:
> > Some display panels would come up with a non-DSI output, those
> > can have an option to connect the DSI host by means of interface
> > bridge converter.
> >
> > This DSI to non-DSI interface bridge converter would requires
> > DSI Host to handle drm bridge functionalities in order to DSI
> > Host to Interface bridge.
> >
> > This patch convert the existing to a drm bridge driver with a
> > built-in encoder support for compatibility with existing
> > component drivers.
> >
> > Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
> > ---
> > Changes for v5:
> > - add atomic APIs
> > - find host and device variant DSI devices.
> > Changes for v4, v3:
> > - none
> >
> >  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c | 112 ++++++++++++++++++++-----
> >  drivers/gpu/drm/sun4i/sun6i_mipi_dsi.h |   7 ++
> >  2 files changed, 96 insertions(+), 23 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > index 43d9c9e5198d..a6a272b55f77 100644
> > --- a/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > +++ b/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c
> > @@ -21,6 +21,7 @@
> >
> >  #include <drm/drm_atomic_helper.h>
> >  #include <drm/drm_mipi_dsi.h>
> > +#include <drm/drm_of.h>
> >  #include <drm/drm_panel.h>
> >  #include <drm/drm_print.h>
> >  #include <drm/drm_probe_helper.h>
> > @@ -713,10 +714,11 @@ static int sun6i_dsi_start(struct sun6i_dsi *dsi,
> >       return 0;
> >  }
> >
> > -static void sun6i_dsi_encoder_enable(struct drm_encoder *encoder)
> > +static void sun6i_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
> > +                                        struct drm_bridge_state *old_bridge_state)
> >  {
> > -     struct drm_display_mode *mode = &encoder->crtc->state->adjusted_mode;
> > -     struct sun6i_dsi *dsi = encoder_to_sun6i_dsi(encoder);
> > +     struct sun6i_dsi *dsi = bridge_to_sun6i_dsi(bridge);
> > +     struct drm_display_mode *mode = &bridge->encoder->crtc->state->adjusted_mode;
> >       struct mipi_dsi_device *device = dsi->device;
> >       union phy_configure_opts opts = { };
> >       struct phy_configure_opts_mipi_dphy *cfg = &opts.mipi_dphy;
> > @@ -772,6 +774,9 @@ static void sun6i_dsi_encoder_enable(struct drm_encoder *encoder)
> >       if (dsi->panel)
> >               drm_panel_prepare(dsi->panel);
> >
> > +     if (dsi->next_bridge)
> > +             dsi->next_bridge->funcs->atomic_pre_enable(dsi->next_bridge, old_bridge_state);
> > +
> >       /*
> >        * FIXME: This should be moved after the switch to HS mode.
> >        *
> > @@ -787,6 +792,9 @@ static void sun6i_dsi_encoder_enable(struct drm_encoder *encoder)
> >       if (dsi->panel)
> >               drm_panel_enable(dsi->panel);
> >
> > +     if (dsi->next_bridge)
> > +             dsi->next_bridge->funcs->atomic_enable(dsi->next_bridge, old_bridge_state);
> > +
>
>
> No need to call the next bridge atomic pre_enable/enable/disable/post_disable since they will
> be called automatically on the bridge chain.

Correct, but the existing bridge chain (stack) is not compatible with
sun6i DSI start sequence. We cannot send any DCS once we start HS
mode.
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/tree/drivers/gpu/drm/sun4i/sun6i_mipi_dsi.c#n775

This specific problem can be fixed only if we change the bridge chain
from stack to queue. Please check this series
https://patchwork.kernel.org/project/dri-devel/patch/20210214194102.126146-6-jagan@amarulasolutions.com/

Jagan.