Hi Neil, Thanks for the patch > Subject: [PATCH] drm/bridge: dw-hdmi: use safe format when first in bridge > chain > > When the dw-hdmi bridge is in first place of the bridge chain, this means > there is now way to select an input format of the dw-hdmi HW component. > > Since introduction of display-connector, negociation was broken since the > dw-hdmi negociation code only worked when the dw-hdmi bridge was in last > position of the bridge chain or behind another bridge also supporting > input & output format negociation. > > Commit 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts > callbacks") was introduced to make negociation work again by making > display-connector act as a pass-through concerning input & output format > negociation. > > But in the case were the dw-hdmi was single in the bridge chain, for > example on Renesas SoCs, with the disply-connector bridge the dw-hdmi is > no more single, breaking output format. > > Reported-by: Biju Das <biju.das.jz@xxxxxxxxxxxxxx> > Bisected-by: Kieran Bingham <kieran.bingham+renesas@xxxxxxxxxxxxxxxx> > Tested-by: Kieran Bingham <kieran.bingham+renesas@xxxxxxxxxxxxxxxx> > Fixes: 0656d1285b79 ("drm/bridge: display-connector: implement bus fmts > callbacks"). > Signed-off-by: Neil Armstrong <narmstrong@xxxxxxxxxxxx> > --- > drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 9 +++++++-- > 1 file changed, 7 insertions(+), 2 deletions(-) > > 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; > + Based on my debugging, this looks redundant, as get_output_bus_fmts already sets output_fmt = MEDIA_BUS_FMT_FIXED, And *num_output_fmts = 1, so the function parameter output_fmt in input_bus_fmts will have MEDIA_BUS_FMT_FIXED And no need to override output_fmt value. I may be wrong here. Regards, Biju > switch (output_fmt) { > /* If MEDIA_BUS_FMT_FIXED is tested, return default bus format */ > case MEDIA_BUS_FMT_FIXED: > -- > 2.25.1