[Intel-gfx] DP Aux interfaces inquiry

Ville Syrjälä ville.syrjala at linux.intel.com
Wed Jan 25 15:56:33 UTC 2017

On Tue, Jan 24, 2017 at 07:51:28PM +0000, Mario.Limonciello at 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).

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.

So I don't think you should be making any assumptions on the
number/order of these device nodes.

> [1] https://github.com/hughsie/fwupd/tree/master/plugins/synapticsmst
> [2] https://github.com/torvalds/linux/commit/e94cb37b34eb8a88fe847438dba55c3f18bf024a
> Thanks,
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> Intel-gfx at lists.freedesktop.org
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Ville Syrjälä
Intel OTC

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