dw_hdmi is showing wrong colour after commit 7cd70656d1285b79("drm/bridge: display-connector: implement bus fmts callbacks")

[Kieran Bingham]

Quoting Neil Armstrong (2022-01-17 13:53:47)
> On 17/01/2022 11:58, Kieran Bingham wrote:
> > Hi Neil,

<big snips to clear up contexts>

> > This fixes the issue for me here on an H3 Salvator-XS.
> > 
> > Could you add...
> > 
> > Bisected-by: Kieran Bingham <kieran.bingham+renesas at ideasonboard.com>
> > Tested-by: Kieran Bingham <kieran.bingham+renesas at ideasonboard.com>
> > 
> > alongside Biju's Reported-by: tag when posting as a fix please?
> 
> 
> Which patch did you test ?

Ah, yes that's not clear is it - sorry! I replied in the wrong place on
the thread when I went back to the mail ... see below...

> >> I'm not happy with this version since it's merely a hack which makes it work.
> >>
> >> Can you test the following change instead, it's correctly handles your situation in a generic manner.
> >>
> >> ========================><=============================
> >> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> >> index 54d8fdad395f..9f2e1cac0ae2 100644
> >> --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> >> +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> >> @@ -2551,8 +2551,9 @@ static u32 *dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
> >>         if (!output_fmts)
> >>                 return NULL;
> >>
> >> -       /* If dw-hdmi is the only bridge, avoid negociating with ourselves */
> >> -       if (list_is_singular(&bridge->encoder->bridge_chain)) {
> >> +       /* If dw-hdmi is the first or only bridge, avoid negociating with ourselves */
> >> +       if (list_is_singular(&bridge->encoder->bridge_chain) ||
> >> +           list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain)) {
> >>                 *num_output_fmts = 1;
> >>                 output_fmts[0] = MEDIA_BUS_FMT_FIXED;
> >>
> >> @@ -2673,6 +2674,10 @@ static u32 *dw_hdmi_bridge_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
> >>         if (!input_fmts)
> >>                 return NULL;
> >>
> >> +       /* If dw-hdmi is the first bridge fall-back to safe output format */
> >> +       if (list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain))
> >> +               output_fmt = MEDIA_BUS_FMT_FIXED;
> >> +
> >>         switch (output_fmt) {
> >>         /* If MEDIA_BUS_FMT_FIXED is tested, return default bus format */
> >>         case MEDIA_BUS_FMT_FIXED:
> >> ========================><=============================

Sorry, I replied in the wrong part of the thread.

Here's the direct diff on my local tree:


diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
index 54d8fdad395f..cac9a87949f1 100644
--- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
+++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
@@ -2551,8 +2551,10 @@ static u32 *dw_hdmi_bridge_atomic_get_output_bus_fmts(struct drm_bridge *bridge,
        if (!output_fmts)
                return NULL;
 
-       /* If dw-hdmi is the only bridge, avoid negociating with ourselves */
-       if (list_is_singular(&bridge->encoder->bridge_chain)) {
+       /* If dw-hdmi is the first or only bridge, avoid negociating with ourselves */
+       if (list_is_singular(&bridge->encoder->bridge_chain) ||
+           list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain)) {
+
                *num_output_fmts = 1;
                output_fmts[0] = MEDIA_BUS_FMT_FIXED;
 
@@ -2673,6 +2675,10 @@ static u32 *dw_hdmi_bridge_atomic_get_input_bus_fmts(struct drm_bridge *bridge,
        if (!input_fmts)
                return NULL;
 
+       /* If dw-hdmi is the first bridge fall-back to safe output format */
+       if (list_is_first(&bridge->chain_node, &bridge->encoder->bridge_chain))
+               output_fmt = MEDIA_BUS_FMT_FIXED;
+
        switch (output_fmt) {
        /* If MEDIA_BUS_FMT_FIXED is tested, return default bus format */
        case MEDIA_BUS_FMT_FIXED:

Which I believe matches the above.

--
Kieran