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authorThomas Zimmermann <tzimmermann@suse.de>2019-01-16 09:13:44 +0100
committerThomas Zimmermann <tzimmermann@suse.de>2019-01-16 09:30:00 +0100
commit3114d3485bd3e3b7a884de637629024e76e9713f (patch)
parent51d2bb6b29d69156237debda83812afe4ded37fa (diff)
drm/fb-helper: Ignore the value of fb_var_screeninfo.pixclock (bsc#1113722)
2 files changed, 79 insertions, 0 deletions
diff --git a/patches.drm/0001-drm-fb-helper-Ignore-the-value-of-fb_var_screeninfo..patch b/patches.drm/0001-drm-fb-helper-Ignore-the-value-of-fb_var_screeninfo..patch
new file mode 100644
index 0000000000..0840dd8cbf
--- /dev/null
+++ b/patches.drm/0001-drm-fb-helper-Ignore-the-value-of-fb_var_screeninfo..patch
@@ -0,0 +1,78 @@
+From 66a8d5bfb518f9f12d47e1d2dce1732279f9451e Mon Sep 17 00:00:00 2001
+From: Ivan Mironov <mironov.ivan@gmail.com>
+Date: Tue, 8 Jan 2019 12:23:53 +0500
+Subject: drm/fb-helper: Ignore the value of fb_var_screeninfo.pixclock
+Git-commit: 66a8d5bfb518f9f12d47e1d2dce1732279f9451e
+Patch-mainline: v5.0-rc2
+References: bsc#1113722
+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@gmail.com>
+Cc: stable@vger.kernel.org
+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@ffwll.ch>
+Link: https://patchwork.freedesktop.org/patch/msgid/20190108072353.28078-3-mironov.ivan@gmail.com
+Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
+ drivers/gpu/drm/drm_fb_helper.c | 7 ++++++-
+ 1 file changed, 6 insertions(+), 1 deletion(-)
+--- a/drivers/gpu/drm/drm_fb_helper.c
++++ b/drivers/gpu/drm/drm_fb_helper.c
+@@ -1526,9 +1526,14 @@ int drm_fb_helper_check_var(struct fb_va
+ 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;
++ }
+ /*
+ * Changes struct fb_var_screeninfo are currently not pushed back
+ * to KMS, hence fail if different settings are requested.
diff --git a/series.conf b/series.conf
index f83381b739..072c70b5ab 100644
--- a/series.conf
+++ b/series.conf
@@ -19712,6 +19712,7 @@
+ patches.drm/0001-drm-fb-helper-Ignore-the-value-of-fb_var_screeninfo..patch
# dhowells/linux-fs keys-uefi