On Thu, 22 Jun 2017 14:29:07 +0200 Andrzej Hajda <a.hajda@xxxxxxxxxxx> wrote: > On 22.06.2017 11:23, Boris Brezillon wrote: > > On Thu, 22 Jun 2017 13:47:43 +0530 > > Archit Taneja <architt@xxxxxxxxxxxxxx> wrote: > > > >> On 06/22/2017 01:20 PM, Benjamin Gaignard wrote: > >>> 2017-06-20 19:31 GMT+02:00 Eric Anholt <eric@xxxxxxxxxx>: > >>>> Archit Taneja <architt@xxxxxxxxxxxxxx> writes: > >>>> > >>>>> On 06/16/2017 08:13 PM, Eric Anholt wrote: > >>>>>> Archit Taneja <architt@xxxxxxxxxxxxxx> writes: > >>>>>> > >>>>>>> On 06/16/2017 02:11 AM, Eric Anholt wrote: > >>>>>>>> If the panel-bridge is being set up after the drm_mode_config_reset(), > >>>>>>>> then the connector's state would never get initialized, and we'd > >>>>>>>> dereference the NULL in the hotplug path. We also need to register > >>>>>>>> the connector, so that userspace can get at it. > >>>>>>>> > >>>>>>> Shouldn't the KMS driver make sure the panel-bridge is set up before > >>>>>>> drm_mode_config_reset? Is it the case when we're inserting the > >>>>>>> panel-bridge driver as a module? > >>>>>>> > >>>>>>> > >>>>>>> All the connectors that have been added are registered automatically > >>>>>>> when drm_dev_register() is called by the KMS driver. Registering a > >>>>>>> connector in the middle of setting up our driver is prone to race > >>>>>>> conditions if the userspace decides to use them immediately. > >>>>>> Yeah, this is fixing initializing panel_bridge at DSI host_attach time, > >>>>>> which in the case of a panel module that creates the DSI device > >>>>>> (adv7533-style, like you said I should use as a reference) will be after > >>>>>> drm_mode_config_reset() and drm_dev_register(). > >>>>> Okay. In the case of the msm kms driver, we defer probe until the > >>>>> adv7533 module is inserted, only then we proceed to drm_mode_config_reset() > >>>>> and drm_dev_register(). I assumed this was the general practice followed by > >>>>> most kms drivers. I.,e the kms driver defers probe until all connector > >>>>> related modules are inserted, and only then proceed to create a drm device. > >>>> The problem, though, is the panel driver needs the MIPI DSI host to > >>>> exist to call mipi_dsi_device_register_full() during the probe process. > >>>> The adv7533 driver gets around this by registering the DSI device in the > >>>> bridge attach step, but drm_panel doesn't have an attach step. > >> I'm not sure how we can get around this. We had discussion about this on irc > >> recently, but couldn't come up with a good conclusion. We could come up with a > >> panel_attach() callback to make it similar to bridges, but that's just us avoiding > >> the real issue. > > How about making DSI dev registration fully asynchronous, that is, DSI > > devs declared in the DT under the DSI host node will be > > registered/attached at probe time, and devs using another control bus > > (like the adv7533 controller over i2c) will be registered afterwards. > > > > That implies moving the drm_brige registration logic outside of the DSI > > host ->probe() path. The idea would be to check if all devs connected > > to the DSI bus are ready at dsi_host->attach() time. If they are, we > > can finally register the XXX -> DSI bridge. If they're not (because > > some devs connected to the DSI bus have not been probed yet), then we > > do not register the drm_bridge and wait for the next dsi_host->attach() > > event. > > I guess you assumes that dsi-host knows all devs connected to it, thanks to: > - subnodes of the host - ie. devices controlled via dsi bus, > - graph links from host ports/endpoints - ie. devices controlled by > other buses, for example adv7533. Yep, but I think that's already a requirement when populating devices with the OF graph method (if one of the DSI output endpoint does not have a drm_bridge/panel attached to it, the DSI host driver returns -EPROBE_DEFER). > > I would separate both abstractions to make it more clear: > 1. MIPI bus should be registered early - to allow create/bind devices on it, Exactly. > 2. drm_bridge should be registered only if all required sinks > (bridges/panels) are registered. That's true, until we find a solution to support add DRM bridge hotplug. > > First point seems OK, I am not sure about the 2nd one - if used > consistently, it would require building pipeline from sink to source. Yes. > By the way is there any pipeline with two consecutive external bridges > in the mainline? I don't know if it exists in mainline, but I had to do that on my FPGA platform when developing/testing Cadence DSI host driver. I had the following chain and it worked just fine: CRTC -> DPI encoder -> DPI to DSI bridge -> DSI to DPI bridge -> DPI to HDMI bridge (adv7511) -> HDMI connector -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
