Re: [PATCH 13/14] drm/bridge: synopsys: Add DW HDMI QP TX controller driver

[Neil Armstrong]

On 05/06/2024 12:11, Cristian Ciocaltea wrote:
> On 6/5/24 12:34 AM, Cristian Ciocaltea wrote:
> > On 6/4/24 11:41 PM, Sam Ravnborg wrote:
> > > Hi Cristian.
> > >
> > > On Tue, Jun 04, 2024 at 10:32:04PM +0300, Cristian Ciocaltea wrote:
> > > > Hi Sam,
> > > >
> > > > On 6/1/24 5:32 PM, Sam Ravnborg wrote:
> > > > > Hi Cristian,
> > > > >
> > > > > a few drive-by comments below.
> > > > >
> > > > > 	Sam
> > > > >
> > > > >
> > > > > > +
> > > > > > +static const struct drm_connector_funcs dw_hdmi_qp_connector_funcs = {
> > > > > > +	.fill_modes = drm_helper_probe_single_connector_modes,
> > > > > > +	.detect = dw_hdmi_connector_detect,
> > > > > > +	.destroy = drm_connector_cleanup,
> > > > > > +	.force = dw_hdmi_qp_connector_force,
> > > > > > +	.reset = drm_atomic_helper_connector_reset,
> > > > > > +	.atomic_duplicate_state = drm_atomic_helper_connector_duplicate_state,
> > > > > > +	.atomic_destroy_state = drm_atomic_helper_connector_destroy_state,
> > > > > > +};
> > > > > > +
> > > > > > +static int dw_hdmi_qp_bridge_attach(struct drm_bridge *bridge,
> > > > > > +				    enum drm_bridge_attach_flags flags)
> > > > > > +{
> > > > > > +	struct dw_hdmi *hdmi = bridge->driver_private;
> > > > > > +
> > > > > > +	if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
> > > > > > +		return drm_bridge_attach(bridge->encoder, hdmi->next_bridge,
> > > > > > +					 bridge, flags);
> > > > > > +
> > > > > > +	return dw_hdmi_connector_create(hdmi, &dw_hdmi_qp_connector_funcs);
> > > > > > +}
> > > > >
> > > > > Are there any users left that requires the display driver to create the
> > > > > connector?
> > > > > In other words - could this driver fail if DRM_BRIDGE_ATTACH_NO_CONNECTOR
> > > > > is not passed and drop dw_hdmi_connector_create()?
> > > > >
> > > > > I did not try to verify this - just a naive question.
> > > >
> > > > I've just tested this and it doesn't work - dw_hdmi_connector_create()
> > > > is still needed.
> > >
> > > Hmm, seems the display driver or some other bridge driver fails to
> > > support "DRM_BRIDGE_ATTACH_NO_CONNECTOR".
> > > what other drivers are involved?
> >
> > Could it be related to the glue driver (updated in the next patch) which
> > is also responsible for setting up the encoder?
> >
> > > Note that my comments here should be seen as potential future
> > > improvements, and do not block the patch from being used.
> >
> > Thanks for the heads up! Will try to get back to this soon and investigate.
>   
> IIUC, modern bridges should not create the connector but rely on display
> drivers to take care of, which in this case is the VOP2 driver. However,
> it also handles some of the older SoCs relying on the non-QP variant of
> DW HDMI IP. Hence the existing dw-hdmi driver would be also impacted in
> order to come up with a proper solution.
>
> A quick check shows there are several users of this IP:
>
> $ git grep -E '= dw_hdmi_(bind|probe)\('
> drivers/gpu/drm/bridge/imx/imx8mp-hdmi-tx.c:    hdmi->dw_hdmi = dw_hdmi_probe(pdev, plat_data);
> drivers/gpu/drm/bridge/synopsys/dw-hdmi.c:      hdmi = dw_hdmi_probe(pdev, plat_data);
> drivers/gpu/drm/imx/ipuv3/dw_hdmi-imx.c:        hdmi->hdmi = dw_hdmi_probe(pdev, match->data);
> drivers/gpu/drm/ingenic/ingenic-dw-hdmi.c:      hdmi = dw_hdmi_probe(pdev, &ingenic_dw_hdmi_plat_data);
> drivers/gpu/drm/meson/meson_dw_hdmi.c:  meson_dw_hdmi->hdmi = dw_hdmi_probe(pdev, &meson_dw_hdmi->dw_plat_data);
> drivers/gpu/drm/renesas/rcar-du/rcar_dw_hdmi.c: hdmi = dw_hdmi_probe(pdev, &rcar_dw_hdmi_plat_data);
> drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c:            hdmi->hdmi = dw_hdmi_bind(pdev, encoder, plat_data);
> drivers/gpu/drm/sun4i/sun8i_dw_hdmi.c:  hdmi->hdmi = dw_hdmi_bind(pdev, encoder, plat_data);
>
> I didn't check which display drivers would be involved, I'd guess there
> are quite a few of them as well. So it seems this ends up being a pretty
> complex task.

If this would be a brand new driver, then it should only support DRM_BRIDGE_ATTACH_NO_CONNECTOR,
so you should not create a connector from the driver.

The fact dw-hdmi accepts an attach without the flag is for legacy purpose
since some DRM drivers haven't switched to DRM_BRIDGE_ATTACH_NO_CONNECTOR yes,
but it's a requirement for new bridges so at some point you'll need to make
sure the rockchip glue and drm driver supports DRM_BRIDGE_ATTACH_NO_CONNECTOR.

This will greatly simplify the driver!

Neil

> Cristian