Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx> writes: > 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. > > With this solution, I think we can avoid the chicken&egg problem where > the adv7533 dev is waiting for the DSI host to be probed to be able to > register a DSI dev with mipi_dsi_device_register_full() and the DSI > host needs all devs to be registered to not return -EPROBE_DEFER. I've now tried having mipi_dsi_device_register_full() succeed early and just do the device-add part when the host shows up. The problem is there's still mipi_dsi_attach(), which needs to be delayed until the panel driver fills in the rest of mipi_dsi_device's fields. Why aren't those part of the info?
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