Re: [PATCH 01/13] drm/atomic: Handle max bpc properties before connector state allocation

[Xilin Wu]

On 9/30/2026 9:26 PM, Dmitry Baryshkov wrote:
> On Wed, Sep 30, 2026 at 08:41:45PM +0800, Xilin Wu wrote:
> > Bridge connectors can attach the max bpc property before their atomic
> > state is allocated by drm_mode_config_reset(). Unconditionally updating
> > connector->state in drm_connector_attach_max_bpc_property() dereferences
> > a NULL pointer in this case. Adding max bpc support to MSM DP and eDP
> > exposes this during display initialization, before a framebuffer console
> > is available.
> >
> > Only update an existing state when attaching the property. Initialize
> > max_requested_bpc and max_bpc from the property range when creating a
> > connector state so that deferred allocation and subsequent resets both
> > restore the default. Avoid leaving the bit depth at zero after reset,
> > which would otherwise cause valid display configurations to be rejected.
> >
> > With MSM DP max bpc support applied, this also restores boot on the Lenovo
> > Yoga Slim 7x.
>
> Hmm?

The boot failure occurred with the later max bpc patch in this series 
applied. I'll drop the "restores boot" sentence and describe this as 
preparatory support instead.

> > Assisted-by: LLM
> > Signed-off-by: Xilin Wu <sophon@xxxxxxxxx>
>
> Can we rather update drm_bridge_connector_init() to register this
> property in non-HDMI cases if max_bpc is more than 8?

Yes, that makes sense. I'll advertise the MSM DP/eDP capability through 
bridge->max_bpc and let drm_bridge_connector_init() attach the property 
for non-HDMI bridges with max_bpc > 8. I'll also handle state creation 
and bpc defaults there, following the HDMI path.

Thanks for the suggestion.


> > ---
> >   drivers/gpu/drm/drm_atomic_state_helper.c | 5 +++++
> >   drivers/gpu/drm/drm_connector.c           | 6 ++++--
> >   2 files changed, 9 insertions(+), 2 deletions(-)


--
Best regards,
Xilin Wu <sophon@xxxxxxxxx>