On Wed, Jan 25, 2017 at 04:43:58PM +0000, Mario.Limonciello@xxxxxxxx wrote: > Thanks for your comments. Some nested below. > > > -----Original Message----- > > From: Ville Syrjälä [mailto:ville.syrjala@xxxxxxxxxxxxxxx] > > Sent: Wednesday, January 25, 2017 9:57 AM > > To: Limonciello, Mario <Mario_Limonciello@xxxxxxxx> > > Cc: intel-gfx@xxxxxxxxxxxxxxxxxxxxx > > Subject: Re: DP Aux interfaces inquiry > > > > On Tue, Jan 24, 2017 at 07:51:28PM +0000, Mario.Limonciello@xxxxxxxx > > wrote: > > > Hi, > > > > > > Recently Synaptics collaborated with Dell on a plugin [1] for fwupd that > > allows flashing Synaptics MST hubs using the DP aux interface to manipulate > > the DPCD [2]. > > > Currently the plugin hardcodes the max number of DP aux devices to look for > > to 3 (as that's what we've seen so far on HW), but we were wondering: > > > > > > 1) If there is a way to query the number of devices that the kernel is > > going to be creating? > > > 2) Are there any instances of more than 3 devices in the wild today that > > anyone is aware of? > > > > These depend on the board you're dealing with, and on the number of gpus you > > have in the system (and whether they actually have drivers loaded for them). > > OK, that's what I was suspecting. > > > > > We should also perhaps expose the aux device node for MST devices. At which > > point the number of aux nodes could change dynamically when you plug MST > > devices in/out. > > > > Hmm, for the devices themselves? The way Synaptics handles cascaded MST devices > today is a remote control mechanism. They're able to turn on remote control > for one MST hub, and it will forward control commands (and payloads) to the next > cascaded hub. I'm not really any kind of MST expert, so I don't really know what people get up to with these things. But there are definitely remote DPCD read/write messages in the spec, so I think we should be able to expose the DPCD of any downstream device via a device node. I took a quick stab at it: git://github.com/vsyrjala/linux.git dp_mst_port_aux_dev Doesn't quite seem to work though, so I probably made a mistake somewhere. > > If/when you do this can you send a uevent up to userspace? It would be good > for fwupd to be able to listen to it and refresh devices based upon what happened > from nodes coming and going. Hotplug uevents should be fired off whenever a new display appears/disappears. -- Ville Syrjälä Intel OTC _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
