Hi
On Thu, Sep 11, 2014 at 3:06 PM, Daniel Vetter daniel@ffwll.ch wrote:
On Thu, Sep 11, 2014 at 02:22:55PM +0200, David Herrmann wrote:
actual-brightness is a bit more tricky. Currently, DRM caches property values, so there is no read_property() hook. We'd have to add this. But it'll be quite nasty as we have to call into the backlight driver. So I think we want to run an async-interruptible worker on the backlight, drop the locks in the ioctl and wait for the job to finish. Not sure whether it's worth it.. maybe we can add this later.
See Jani's reply - we probably don't need it, at least not in version 1.
I couldn't see any comment regarding "actual-brightness". But I'm totally fine with dropping this.
- How does udev match on the drm connector name? They are not terribly stable atm, and if you reload your drm driver, or much more likely, have two gpus with two drm drivers they change. We probably should change the name allocation scheme to be per device instance instead of global first. Within a driver probe order is hopefully deterministic on a given platform, since even with super dynamic setups (based on dt/acpi) the firmware tables should change really.
You can match on EDID attributes. Ok, so far this is pretty ugly as the EDID property is binary. But we can add rather trivial udev extensions to make EDID binary against text matching possible.
Why EDID? This is purely about the drm connector name, e.g. if I have 2 gpus, both with an eDP connector (optimus, so just one panel) then the first driver gets eDP-1 as the name of it and the 2nd one eDP-2. Which is ok if both should control backlight brightness through the same driver, but a total mess if not just gpus get switched, but also backlight controllers.
And if you reload you get then eDP-2 and eDP-3. Well at least in the past, that hilarity at least was fixed in
commit b21e3afe2357c0f49348a5fb61247012bf8262ec Author: Ilia Mirkin imirkin@alum.mit.edu Date: Wed Aug 7 22:34:48 2013 -0400
drm: use ida to allocate connector idWhat I think we need to do is to make these ida allocators per-device, so that both drivers have an eDP-1 connector. Otherwise you need to either match both or do funny tricks like "the first eDP connector, no matter which one on this gpu". After all we can now support more than one eDP (and more than one LVDS since a long time actually).
Or how exactly is the udev hw db supposed to match this stuff for special cases. In general we need to duplicate the existing logic from libbacklight, like Matthew suggested.
Yeah, I get what you mean. Names are not stable so even if we can match on the internal card, we cannot match on "lowest available eDP display". per-device IDs should be totally fine and fix this issue. We prefix connectors with the device name anyway, so no conflicts can arise.
But I think we want to make this a udev builtin anyway. So we can easily implement the same logic as libbacklight.
Thanks David