On 01.12.2016 16:12, Daniel Vetter wrote: > On Thu, Dec 01, 2016 at 02:22:18PM +0100, Andrzej Hajda wrote: >> On 01.12.2016 08:18, Daniel Vetter wrote: >>> On Thu, Dec 01, 2016 at 08:07:29AM +0100, Andrzej Hajda wrote: >>>> On 30.11.2016 14:09, Daniel Vetter wrote: >>>>> On Wed, Nov 30, 2016 at 01:03:20PM +0200, Laurent Pinchart wrote: >>>>>> On Wednesday 30 Nov 2016 11:55:20 Daniel Vetter wrote: >>>>>>> Why exactly do you want to hotplug encoders? Or bridges fwiw ... since at >>>>>>> least only making those hotpluggable will make the uabi story easier since >>>>>>> they're not exposed. >>>>>> Ideally to avoid disabling the whole display engine when one encoder isn't >>>>>> available/operational. Right now we're waiting for all pieces to be available >>>>>> (using deferred probing or the component framework) before registering the DRM >>>>>> device. This means that if one bridge can't be probed successfully for any >>>>>> reason we'll end up having not display at all. This includes the case where >>>>>> the driver for the bridge is not available. If we could support dynamic >>>>>> hotplug of bridges, we could start with a display engine that supports a >>>>>> subset of the outputs, and add new outputs as they become operational. >>>>>> >>>>>> We have a similar issue when unbinding bridge devices from their driver. They >>>>>> obviously can't be used anymore, but we have no solution to handle that apart >>>>>> from unregistering the DRM device completely, as otherwise rebinding the >>>>>> bridge to the driver later can't be handled. >>>>> This all sounds pretty cool, but does anyone care? Like what's the >>>>> real-world use-case here? Some cosmic ray destroyed the bridge driver on >>>>> your android phone and now you want it to magically fall back to hdmi that >>>>> no one ever plugs in? Or someone misconfigures their kernel and gets >>>>> greeted with a black screen, instead of a ... black screen? >>>> Real use case is that we need to always load hdmi path drivers at phone >>>> startup just in case somebody will use it. >>>> This way we are wasting space and more importantly boot time, for code >>>> which won't be used by 99% users of phones. >>>> Putting them into modules an loading on MHL/HDMI cable plug-in would be >>>> more optimal, I guess. >>> Do we have numbers for this? >> For number of HDMI/MHL users in mobiles, I have no stats :) >> For display boot delay due to deferring hdmi driver is 2.5-3.5 seconds >> on peach-pi board for example [1]. > That sounds horrible. We load our entire driver in that time, and it has 3 > hdmi ports. What exactly is that thing doing for 3 seconds?! Until we know > what's going on I'm not sure it's just a driver that has a dead-slow init > function ... As I wrote it is due to deferring probe of hdmi driver. It has nothing to do with device initialization. > >> [1]: >> https://storage.kernelci.org/ulfh/v4.9-rc7-120-g38cdf7e0bfee/arm-exynos_defconfig/lab-baylibre-seattle/boot-exynos5800-peach-pi.html >> >> >>> What part of the overhead is the edid probing >>> and reading, which we probably should optimize either way ... optimize as >>> in make sure we never ever stall anything for edid reads. >> As EDID probing should be performed only after detecting sink it seems >> irrelevant here. >> >>> And if you never load the hdmi driver, how do you know when to load it >>> because the user plugged in the cable? >> Mobiles often have detection which cable is plugged in. However I am not >> sure if kernel sends such events to userspace, >> but this should be simple to do. > Well, to do that (at least with drm) you need the driver loaded, or at > least the stuff it supports registered. > -Daniel Fortunately, in case of mobiles, cable detection is usually done outside of DRM via extcon driver. Regards Andrzej _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
