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. Another alternative is my original version of the panel driver that was a mipi_dsi_device driver that registered the panel during the DSI device probe. That's why vc4's panel lookup is during the MIPI DSI attach phase, currently.
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