On Sat, Jan 05, 2019 at 09:21:21PM +0500, Ivan Mironov wrote: > On Fri, 2018-12-28 at 13:06 +0100, Daniel Vetter wrote: > > On Fri, Dec 28, 2018 at 04:13:08AM +0500, Ivan Mironov wrote: > > > 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. > > > > > > Feel free to NAK this patch if you think that it causes breakage of > > > user-space =). > > > > It's a regression, we don't nack regression fixes :-) > > > > > 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> > > > > I thought this is also a regression fix, so also needs Fixes: and cc: > > stable? > > -Daniel > > This particular patch fixes a bug that existed for 10 years unnoticed. > Are "Fixes:" and "Cc: stable" really required? If you want it backported into a stable kernel release, then yes, they are needed :) thanks, greg k-h _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
