Re: [PATCH v22 02/18] ui/sdl2: Don't disable scanout when display is refreshed

["Alex Bennée" <alex.bennee@linaro.org>]

Stefan Weil <sw@weilnetz.de> writes:

> Am 03.03.26 um 16:14 schrieb Dmitry Osipenko:
>> Display refreshment is invoked by a timer and it erroneously disables
>> the active scanout if it happens to be invoked after scanout has been
>> enabled. This offending scanout-disable race condition with a timer
>> can be easily hit when Qemu runs with a disabled vsync by using SDL or
>> GTK displays (with vblank_mode=0 for GTK). Refreshment of display's
>> content shouldn't disable the active display. Fix it by keeping the
>> scanout's state unchanged when display is redrawn.
>> Reviewed-by: Akihiko Odaki <akihiko.odaki@daynix.com>
>> Acked-by: Michael S. Tsirkin <mst@redhat.com>
>> Tested-by: Alex Bennée <alex.bennee@linaro.org>
>> Acked-by: Pierre-Eric Pelloux-Prayer <pierre-eric.pelloux-prayer@amd.com>
>> Reviewed-by: Yiwei Zhang <zzyiwei@gmail.com>
>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
>> ---
>>   ui/sdl2-gl.c | 1 -
>>   1 file changed, 1 deletion(-)
>> diff --git a/ui/sdl2-gl.c b/ui/sdl2-gl.c
>> index 3be17d1079af..5eca0248233e 100644
>> --- a/ui/sdl2-gl.c
>> +++ b/ui/sdl2-gl.c
>> @@ -51,7 +51,6 @@ static void sdl2_gl_render_surface(struct sdl2_console *scon)
>>       int ww, wh;
>>         SDL_GL_MakeCurrent(scon->real_window, scon->winctx);
>> -    sdl2_set_scanout_mode(scon, false);
>>         SDL_GetWindowSize(scon->real_window, &ww, &wh);
>>       surface_gl_setup_viewport(scon->gls, scon->surface, ww, wh);
>
> I got a user report that my latest QEMU for Windows no longer supports
> SDL. According to my own test, SDL still worked with git master
> (2026-03-07), but was broken with 11.0.0-rc0 (2026-03-18).

This is:

  https://gitlab.com/qemu-project/qemu/-/work_items/3347

Anthony should be posting a patch to the list soon.

>
> Therefore this patch series might have caused the regression which
> still exists in 11.0.0-rc2. All test installers are available here:
> https://qemu.weilnetz.de/w64/2026/.
>
> Regards
> Stefan Weil

-- 
Alex Bennée
Virtualisation Tech Lead @ Linaro