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 > --- > 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 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
