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? "pixclock != 0" check was introduced in this file by 785b93ef8c309 ("drm/kms: move driver specific fb common code to helper functions (v2)"). But actually similar code existed in the device-specific drivers even earlier. > > > --- > > drivers/gpu/drm/drm_fb_helper.c | 7 ++++++- > > 1 file changed, 6 insertions(+), 1 deletion(-) > > > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c > > index aff576c3c4fb..b95a0c23c7c8 100644 > > --- a/drivers/gpu/drm/drm_fb_helper.c > > +++ b/drivers/gpu/drm/drm_fb_helper.c > > @@ -1690,9 +1690,14 @@ int drm_fb_helper_check_var(struct fb_var_screeninfo *var, > > struct drm_fb_helper *fb_helper = info->par; > > struct drm_framebuffer *fb = fb_helper->fb; > > > > - if (var->pixclock != 0 || in_dbg_master()) > > + if (in_dbg_master()) > > return -EINVAL; > > > > + if (var->pixclock != 0) { > > + DRM_DEBUG("fbdev emulation doesn't support changing the pixel clock, value of pixclock is ignored\n"); > > + var->pixclock = 0; > > + } > > + > > if ((drm_format_info_block_width(fb->format, 0) > 1) || > > (drm_format_info_block_height(fb->format, 0) > 1)) > > return -EINVAL; > > -- > > 2.20.1 > > _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
