On Fri, 23 Jun 2017 09:22:15 +0200 Andrzej Hajda <a.hajda@xxxxxxxxxxx> wrote: > On 22.06.2017 15:34, Boris Brezillon wrote: > > On Thu, 22 Jun 2017 15:16:47 +0200 > > Andrzej Hajda <a.hajda@xxxxxxxxxxx> wrote: > > > >> On 22.06.2017 14:41, Boris Brezillon wrote: > >>> 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. > >> Since drm_bridge_attach requires encoder to be not null pipeline > >> creation would be painful: > >> 1. Every driver must call drm_of_find_panel_or_bridge on sink(s) before > >> registering bridge and cache the result for later use. > > Shouldn't be hard to do since dsi_host->attach() is called each time a > > sink is added (and ready to use). All you need to do is retrieve the > > bridge pointer and put it in a list embedded in the DSI host priv > > struct. Once you have all sinks added to this list (can be checked by > > counting the number of endpoints and DSI devs at probe time), you can > > register the DSI bridge and wait for someone to call ->attach() on it. > > > > In the ->attach() hook of the DSI bridge, you'll have to attach all > > sinks stored in the list to the DSI bridge. Note that right now you have > > a 1:1 relationship, which prevents you from having one DSI bridge that > > can attach to different bridges available on the DSI bus (e.g. DSI -> > > HDMI bridge on channel 0 and DSI -> LVDS bridge on channel 1). > > > >> 2. After encoder finds directly connected bridge, it can attach it. > > I don't get that one. > > If you have pipeline: > > crtc -> encoder -> bridge1 -> bridge2 -> panel > > encoder knows only about bridge1, and must wait till it is registered, > before attaching it, > and assuming bridge must wait for its sinks before registration the > whole pipeline construction will look like: > > 0. encoder waits for bridge1, bridge1 waits for bridge2, bridge2 waits > for panel, usually by deferring. > 1. panel is registered. > 2. bridge2 finds panel and is registered. > 3. bridge1 finds bridge2 and is registered. > 4. encoder finds bridge1 and attach it to encoder, > 4a. bridge1->attach() attach bridge2 to encoder after bridge1 > 4b. bridge2->attach() attach panel to bridge2 > > This is why it seems for me quite complicated. But that's already what happens in most drivers today (probably because things were designed before connector hotplug was supported). I agree, it's far from ideal, but until we get full-hotplug support, we'll have to rely on such hacks. -- 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
