[PATCH v8 02/39] drm/connector: Add caps-based HDMI connector init helper

[Maxime Ripard]

On Fri, Jul 03, 2026 at 10:31:55PM +0300, Cristian Ciocaltea wrote:
> Hi Dmitry,
> 
> Thanks for your quick review!
> 
> On 7/3/26 5:05 PM, Dmitry Baryshkov wrote:
> > On Thu, Jul 02, 2026 at 05:46:15PM +0300, Cristian Ciocaltea wrote:
> >> In preparation for adding HDMI 2.x source capabilities, introduce struct
> >> drm_connector_hdmi_caps and a new drmm_connector_hdmi_init_with_caps()
> >> helper.
> >>
> >> The existing drmm_connector_hdmi_init() helper currently takes
> >> individual capability arguments such as supported_formats and max_bpc.
> >> Adding more HDMI-specific arguments to that function would not scale
> >> well, so move those values into a dedicated capabilities structure and
> >> implement the existing helper as a wrapper around the new caps-based
> >> interface.
> > 
> > I think, it was an intention of Maxime: make sure that every driver is
> > forced to provide some values here. With the struct-based init it is
> > easy to overlook or to ommit a value.
> 
> Agreed that the struct-based init loses the compile-time guarantee that every
> argument is explicitly provided - that's a real downside.  
> 
> I'd argue it's recoverable, though: the init helper validates the mandatory
> fields, so a driver that omits a required value gets rejected at init time
> rather than silently misconfigured.  The "you must provide sane values" property
> is expected to be preserved, just enforced at runtime instead of by the
> compiler. 

Yeah, I don't think we can win with C here. Rust might, but we're
probably a long way from that.

> The main motivation for the struct is scalability/maintainability as we add HDMI
> 2.x capabilities: new fields go into the struct rather than growing the helper's
> argument list, so existing callers don't need churny signature updates on every
> extension.
> 
> FWIW, in the previous revision we discussed addressing the concern with a
> callback instead.  Sadly, I had to discard that approach, as it proved not
> flexible enough, e.g. drm_bridge_connector_init() computes caps dynamically, and
> would have required either stateful callbacks, or storing redundant/temporary
> cap data in driver-private structures just to satisfy the callback.

I just realized something reviewing your patch: we don't necessarily
need an extra argument or a callback, we can just put these fields into
drm_hdmi_connector_funcs directly, and then validate them in init.

Maxime
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