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]. [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. Regards Andrzej _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
