Hi Paul, > Am 23.09.2021 um 15:30 schrieb Paul Cercueil <paul@xxxxxxxxxxxxxxx>: > > Hi Nikolaus, > > Le jeu., sept. 23 2021 at 13:41:28 +0200, H. Nikolaus Schaller <hns@xxxxxxxxxxxxx> a écrit : >> Hi Laurent, >> Ah, ok. >> But then we still have issues. >> Firstly I would assume that get_edid only works properly if it is initialized >> through dw_hdmi_connector_create(). >> Next, in the current code, passing DRM_BRIDGE_ATTACH_NO_CONNECTOR to >> dw_hdmi_bridge_attach() indeed does not call dw_hdmi_connector_create() >> but returns 0. >> This patch 6/6 makes drm/ingenic unconditionally require a connector >> to be attached which is defined somewhere else (device tree e.g. "connector-hdmi") >> unrelated to dw-hdmi. Current upstream code for drm/ingenic does not init/attach >> such a connector on its own so it did work before. >> I.e. I think we can't just use parts of dw-hdmi. > > The fact that Laurent is using dw-hdmi with DRM_BRIDGE_ATTACH_NO_CONNECTOR on Renesas makes me think that it's possible here as well. There's no reason why it shouldn't work with ingenic-drm. That is interesting and Laurent can probably comment on differences between his setup (I wasn't able to deduce what device you are referring to) and dw-hdmi. For jz4780 we tried that first. I do not remember the exact reasons but we wasted weeks trying to but failed to get it working. While the dw-hdmi connector simply works on top of upstream and fails only if we apply your patch. Another issue is how you want to tell connector-hdmi to use the extra i2c bus driver for ddc which is not available directly as a standard i2c controller of the jz4780. hdmi-connector.yaml defines: ddc-i2c-bus: description: phandle link to the I2C controller used for DDC EDID probing $ref: /schemas/types.yaml#/definitions/phandle So we would need some ddc-i2c-bus = <&i2c-controller-inside-the dw-hdmi>. But that i2c-controller-inside-the dw-hdmi does not exist in device tree and can not be added unless someone significantly rewrites dw-hdmi to register and expose it as i2c controller. > > The ingenic-drm driver does not need to create any connector. The "connector-hdmi" is connected to dw-hdmi as the "next bridge" in the list. Sure. It does not *create* a connector. It expects that it can safely call drm_bridge_connector_init() to get a pointer to a newly created connector. But if we use the dw-hdmi connector, there is no such connector and "next bridge". Or can you tell me how to make the dw-hdmi connector created by dw_hdmi_connector_create() become the "next bridge" in the list for your driver? But without significantly rewriting dw-hdmi.c (and testing). > >> If drm_bridge_attach() would return some errno if DRM_BRIDGE_ATTACH_NO_CONNECTOR >> is set, initialization in ingenic_drm_bind() would fail likewise with "Unable to attach bridge". >> So in any case dw-hdmi is broken by this drm/ingenic patch unless someone >> reworks it to make it compatible. > > Where would the errno be returned? Why would drm_bridge_attach() return an error code? Currently dw_hdmi_bridge_attach() returns 0 if it is asked to support DRM_BRIDGE_ATTACH_NO_CONNECTOR. This is not treated as an error by drm_bridge_attach(). Here it could return an error (-ENOTSUPP?) instead, to allow for error handling by its caller. But that raises an error message like "failed to attach bridge to encoder" and the bridge is reset and detached. > >> Another issue is that dw_hdmi_connector_create() does not only do dcd/edid >> but appears to detects hot plug and does some special initialization. >> So we probably loose hotplug detect if we just use drm_bridge_funcs.get_edid(). > > There's drm_bridge_funcs.detect(). You mean in dw-hdmi? Yes, it calls dw_hdmi_bridge_detect() which calls dw_hdmi_detect(). This does some read_hpd. Anyways, this does not solve the problem that with your drm/ingenic proposal the dw-hdmi subsystem (hdmi + ddc) can no longer be initialized properly unless someone fixes either. So IMHO this should be treated as a significant blocking point for your patch because it breaks something that is working upstream and there seems to be no rationale to change it. Your commit message just says: "All the bridges are now attached with DRM_BRIDGE_ATTACH_NO_CONNECTOR." but gives no reason why. I fully understand that you want to change it and Laurent said that it will become standard in the far future. Therefore I suggest to find a way that you can find out if a connector has already been created by drm_bridge_attach() to stay compatible with current upstream code. I even want to help here but I don't know how to detect the inverse of drm_connector_attach_encoder(), i.e. is_drm_encoder_attached_to_any_connector(). BR and thanks, Nikolaus
