On Thu, Jan 17, 2019 at 08:02:33AM +0500, Ivan Mironov wrote: > commit 66a8d5bfb518f9f12d47e1d2dce1732279f9451e upstream. > > Backported by adjusting patch context. > > Strict requirement of pixclock to be zero breaks support of SDL 1.2 > which contains hardcoded table of supported video modes with non-zero > pixclock values[1]. > > To better understand which pixclock values are considered valid and how > driver should handle these values, I briefly examined few existing fbdev > drivers and documentation in Documentation/fb/. And it looks like there > are no strict rules on that and actual behaviour varies: > > * some drivers treat (pixclock == 0) as "use defaults" (uvesafb.c); > * some treat (pixclock == 0) as invalid value which leads to > -EINVAL (clps711x-fb.c); > * some pass converted pixclock value to hardware (uvesafb.c); > * some are trying to find nearest value from predefined table > (vga16fb.c, video_gx.c). > > Given this, I believe that it should be safe to just ignore this value if > changing is not supported. It seems that any portable fbdev application > which was not written only for one specific device working under one > specific kernel version should not rely on any particular behaviour of > pixclock anyway. > > However, while enabling SDL1 applications to work out of the box when > there is no /etc/fb.modes with valid settings, this change affects the > video mode choosing logic in SDL. Depending on current screen > resolution, contents of /etc/fb.modes and resolution requested by > application, this may lead to user-visible difference (not always): > image will be displayed in a right way, but it will be aligned to the > left instead of center. There is no "right behaviour" here as well, as > emulated fbdev, opposing to old fbdev drivers, simply ignores any > requsts of video mode changes with resolutions smaller than current. > > The easiest way to reproduce this problem is to install sdl-sopwith[2], > remove /etc/fb.modes file if it exists, and then try to run sopwith > from console without X. At least in Fedora 29, sopwith may be simply > installed from standard repositories. > > [1] SDL 1.2.15 source code, src/video/fbcon/SDL_fbvideo.c, vesa_timings > [2] http://sdl-sopwith.sourceforge.net/ > > Signed-off-by: Ivan Mironov <mironov.ivan@xxxxxxxxx> > Cc: stable@xxxxxxxxxxxxxxx # 4.14.x > Cc: stable@xxxxxxxxxxxxxxx # 4.19.x > Cc: stable@xxxxxxxxxxxxxxx # 4.20.x > Fixes: 79e539453b34e ("DRM: i915: add mode setting support") > Fixes: 771fe6b912fca ("drm/radeon: introduce kernel modesetting for radeon hardware") > Fixes: 785b93ef8c309 ("drm/kms: move driver specific fb common code to helper functions (v2)") > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxx> > Link: https://patchwork.freedesktop.org/patch/msgid/20190108072353.28078-3-mironov.ivan@xxxxxxxxx > --- > drivers/gpu/drm/drm_fb_helper.c | 7 ++++++- > 1 file changed, 6 insertions(+), 1 deletion(-) All now queued up, thanks. greg k-h
