Hi Mario, please see below... On Wed, Jan 25, 2017 at 04:43:58PM +0000, mario.limoncie...@dell.com wrote: > Thanks for your comments. Some nested below. > > > -----Original Message----- > > From: Ville Syrjälä [mailto:ville.syrj...@linux.intel.com] > > Sent: Wednesday, January 25, 2017 9:57 AM > > To: Limonciello, Mario <mario_limoncie...@dell.com> > > Cc: intel-gfx@lists.freedesktop.org > > Subject: Re: [Intel-gfx] DP Aux interfaces inquiry > > > > On Tue, Jan 24, 2017 at 07:51:28PM +0000, mario.limoncie...@dell.com > > 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. > > 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. > > > So I don't think you should be making any assumptions on the number/order of > > these device nodes. > > > > From userspace would it be better to just scan /dev for /dev/drm_dp_aux# > nodes? > No assumptions about the order of them, just look for all the ones with that > prefix? > > If not, do you have a better recommendation on how to do this?
Alternatively, you can also scan /sys/class/drm_dp_aux_dev/. The number of the files that you have there should match what you have inside /dev. It's not necessarily better though. Regards, Rafael _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/intel-gfx
