Hi Thomas Thanks for the response. On Thu, 12 Oct 2023 at 08:03, Thomas Zimmermann <tzimmermann@xxxxxxx> wrote: > > Hi Dave > > Am 11.10.23 um 17:52 schrieb Dave Stevenson: > > Hi Thomas (and everyone else) > > > > Maxime has suggested you're the person for DRM framebuffer emulation. > > > > I'm getting some unexpected behaviour when there are multiple DRM > > drivers in play. In this case it happens to be vc4 and the tiny > > hx8357d SPI display driver, but this affects most of the tiny DRM > > drivers and also the DSI and DPI outputs on the Pi5. > > We get different behaviour depending on whether vc4 or hx8357d > > initialises first. > > > > If hx8357d loads first and registers as /dev/fb0 through the fb > > emulation, then we get fbcon enabling the display and putting the > > emulated framebuffer on it. vc4 then loads, registers /dev/fb1, and > > through the hotplug handler it enables the display > > (drm_fb_helper_hotplug_event calls, drm_fb_helper_set_par, which calls > > __drm_fb_helper_restore_fbdev_mode_unlocked). > > > > If vc4 loads first and claims /dev/fb0, fbcon initalises and enables > > the display. hx8357d then loads and registers as /dev/fb1. fbcon is > > not configured for that fb, and there is no subsequent hotplug event > > (SPI displays aren't hotpluggable), so we have a fully configured > > framebuffer exposed to userspace but the display itself isn't enabled > > so we don't see anything :-( > > Open and close /dev/dri/card1 and the lastclose hook calls > > drm_fb_helper_restore_fbdev_mode_unlocked and we get the display > > enabled. > > What you're describing sounds like the recent bug report at > > https://gitlab.freedesktop.org/drm/amd/-/issues/2649 > > which had similar symptoms with amdgpu. IIRC the console didn't > initialize if the DRM hotplugging event happened before fbdev emulation > was ready. DRM's fbdev code would then not see the hotplugged connector. > > Do you have commit 27655b9bb9f0 ("drm/client: Send hotplug event after > registering a client") in your tree? (It's been ported into various > stable branches as well.) I was about to switch from my 6.1.55 build to the latest just to ensure it hadn't been fixed, but that commit hit the 6.1 stable branch in 6.1.43, so I do have it. Other priorities have overtaken my investigation of this, but at least knowing that it should enable the outputs (and nominally through the hotplug hook) I can have another look at what is actually going on. Thanks again Dave > Best regard > Thomas > > > > > Is it intentional that we're left in this limbo state with the display > > not enabled if fbcon isn't enabled on a framebuffer? > > > > We're trying to get people to transition from the fbdev drivers to DRM > > equivalents, but this seems to be a backwards step if there is an > > extra step required to get the display enabled. Many users are still > > just using the framebuffer. > > > > Any input is much appreciated. > > > > Thanks, > > Dave > > -- > Thomas Zimmermann > Graphics Driver Developer > SUSE Software Solutions Germany GmbH > Frankenstrasse 146, 90461 Nuernberg, Germany > GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman > HRB 36809 (AG Nuernberg)
