On Thu, 26 Oct 2023 at 11:07, Maxime Ripard mripard@kernel.org wrote:
On Thu, Oct 26, 2023 at 01:23:53AM +0300, Dmitry Baryshkov wrote:
+static int starfive_hdmi_register(struct drm_device *drm, struct starfive_hdmi *hdmi) +{
- struct drm_encoder *encoder = &hdmi->encoder;
- struct device *dev = hdmi->dev;
- encoder->possible_crtcs = drm_of_find_possible_crtcs(drm, dev->of_node);
- /*
- If we failed to find the CRTC(s) which this encoder is
- supposed to be connected to, it's because the CRTC has
- not been registered yet. Defer probing, and hope that
- the required CRTC is added later.
- */
- if (encoder->possible_crtcs == 0)
return -EPROBE_DEFER;- drm_encoder_helper_add(encoder, &starfive_hdmi_encoder_helper_funcs);
- hdmi->connector.polled = DRM_CONNECTOR_POLL_HPD;
- drm_connector_helper_add(&hdmi->connector,
&starfive_hdmi_connector_helper_funcs);- drmm_connector_init(drm, &hdmi->connector,
&starfive_hdmi_connector_funcs,DRM_MODE_CONNECTOR_HDMIA,On an embedded device one can not be so sure. There can be MHL or HDMI Alternative Mode. Usually we use drm_bridge here and drm_bridge_connector.
On an HDMI driver, it's far from being a requirement, especially given the limitations bridges have.
It's a blessing that things like MHL / HDMI-in-USB-C / HDMI-to-MyDP are not widely used in the wild and are mostly non-existing except several phones that preate wide DP usage. Using drm_connector directly prevents one from handling possible modifications on the board level. For example, with the DRM connector in place, handling a separate HPD GPIO will result in code duplication from the hdmi-connector driver. Handling any other variations in the board design (which are pretty common in the embedded world) will also require changing the driver itself. drm_bridge / drm_bridge_connector save us from those issues.
BTW: what are the limitations of the drm_bridge wrt. HDMI output? I'm asking because we heavily depend on the bridge infrastructure for HDMI output. Maybe we are missing something there, which went unnoticed to me and my colleagues.