On Wed, Jun 24, 2020 at 5:29 AM Daniel Vetter <daniel.vetter@xxxxxxxx> wrote: > > In the past we had a pile of hacks to orchestrate access between fbdev > emulation and native kms clients. We've tried to streamline this, by > always preferring the kms side above fbdev calls when a drm master > exists, because drm master controls access to the display resources. > > Unfortunately this breaks existing userspace, specifically Xorg. When > exiting Xorg first restores the console to text mode using the KDSET > ioctl on the vt. This does nothing, because a drm master is still > around. Then it drops the drm master status, which again does nothing, > because logind is keeping additional drm fd open to be able to > orchestrate vt switches. In the past this is the point where fbdev was > restored, as part of the ->lastclose hook on the drm side. > > Now to fix this regression we don't want to go back to letting fbdev > restore things whenever it feels like, or to the pile of hacks we've > had before. Instead try and go with a minimal exception to make the > KDSET case work again, and nothing else. > > This means that if userspace does a KDSET call when switching between > graphical compositors, there will be some flickering with fbcon > showing up for a bit. But a) that's not a regression and b) userspace > can fix it by improving the vt switching dance - logind should have > all the information it needs. > > While pondering all this I'm also wondering wheter we should have a > SWITCH_MASTER ioctl to allow race-free master status handover. But > that's for another day. > > v2: Somehow forgot to cc all the fbdev people. > > Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=208179 > Cc: shlomo@xxxxxxxxxxxx > Reported-and-Tested-by: shlomo@xxxxxxxxxxxx > Cc: Michel Dänzer <michel@xxxxxxxxxxx> > Fixes: 64914da24ea9 ("drm/fbdev-helper: don't force restores") > Cc: Noralf Trønnes <noralf@xxxxxxxxxxx> > Cc: Thomas Zimmermann <tzimmermann@xxxxxxx> > Cc: Daniel Vetter <daniel.vetter@xxxxxxxxx> > Cc: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx> > Cc: Maxime Ripard <mripard@xxxxxxxxxx> > Cc: David Airlie <airlied@xxxxxxxx> > Cc: Daniel Vetter <daniel@xxxxxxxx> > Cc: dri-devel@xxxxxxxxxxxxxxxxxxxxx > Cc: <stable@xxxxxxxxxxxxxxx> # v5.7+ > Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@xxxxxxxxxxx> > Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> > Cc: Nathan Chancellor <natechancellor@xxxxxxxxx> > Cc: Qiujun Huang <hqjagain@xxxxxxxxx> > Cc: Peter Rosin <peda@xxxxxxxxxx> > Cc: linux-fbdev@xxxxxxxxxxxxxxx > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> > --- > drivers/gpu/drm/drm_fb_helper.c | 63 +++++++++++++++++++++++++------- > drivers/video/fbdev/core/fbcon.c | 3 +- > include/uapi/linux/fb.h | 1 + > 3 files changed, 52 insertions(+), 15 deletions(-) > > diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c > index 170aa7689110..ae69bf8e9bcc 100644 > --- a/drivers/gpu/drm/drm_fb_helper.c > +++ b/drivers/gpu/drm/drm_fb_helper.c > @@ -227,18 +227,9 @@ int drm_fb_helper_debug_leave(struct fb_info *info) > } > EXPORT_SYMBOL(drm_fb_helper_debug_leave); > > -/** > - * drm_fb_helper_restore_fbdev_mode_unlocked - restore fbdev configuration > - * @fb_helper: driver-allocated fbdev helper, can be NULL > - * > - * This should be called from driver's drm &drm_driver.lastclose callback > - * when implementing an fbcon on top of kms using this helper. This ensures that > - * the user isn't greeted with a black screen when e.g. X dies. > - * > - * RETURNS: > - * Zero if everything went ok, negative error code otherwise. > - */ > -int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper) > +static int > +__drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper, > + bool force) > { > bool do_delayed; > int ret; > @@ -250,7 +241,16 @@ int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper) > return 0; > > mutex_lock(&fb_helper->lock); > - ret = drm_client_modeset_commit(&fb_helper->client); > + if (force) { > + /* > + * Yes this is the _locked version which expects the master lock > + * to be held. But for forced restores we're intentionally > + * racing here, see drm_fb_helper_set_par(). > + */ > + ret = drm_client_modeset_commit_locked(&fb_helper->client); > + } else { > + ret = drm_client_modeset_commit(&fb_helper->client); > + } > > do_delayed = fb_helper->delayed_hotplug; > if (do_delayed) > @@ -262,6 +262,22 @@ int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper) > > return ret; > } > + > +/** > + * drm_fb_helper_restore_fbdev_mode_unlocked - restore fbdev configuration > + * @fb_helper: driver-allocated fbdev helper, can be NULL > + * > + * This should be called from driver's drm &drm_driver.lastclose callback > + * when implementing an fbcon on top of kms using this helper. This ensures that > + * the user isn't greeted with a black screen when e.g. X dies. > + * > + * RETURNS: > + * Zero if everything went ok, negative error code otherwise. > + */ > +int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper) > +{ > + return __drm_fb_helper_restore_fbdev_mode_unlocked(fb_helper, false); > +} > EXPORT_SYMBOL(drm_fb_helper_restore_fbdev_mode_unlocked); > > #ifdef CONFIG_MAGIC_SYSRQ > @@ -1318,6 +1334,7 @@ int drm_fb_helper_set_par(struct fb_info *info) > { > struct drm_fb_helper *fb_helper = info->par; > struct fb_var_screeninfo *var = &info->var; > + bool force; > > if (oops_in_progress) > return -EBUSY; > @@ -1327,7 +1344,25 @@ int drm_fb_helper_set_par(struct fb_info *info) > return -EINVAL; > } > > - drm_fb_helper_restore_fbdev_mode_unlocked(fb_helper); > + /* > + * Normally we want to make sure that a kms master takes > + * precedence over fbdev, to avoid fbdev flickering and > + * occasionally stealing the display status. But Xorg first sets > + * the vt back to text mode using the KDSET IOCTL with KD_TEXT, > + * and only after that drops the master status when exiting. > + * > + * In the past this was caught by drm_fb_helper_lastclose(), but > + * on modern systems where logind always keeps a drm fd open to > + * orchestrate the vt switching, this doesn't work. > + * > + * To no break the userspace ABI we have this special case here, "To not break" With that fixed: Reviewed-by: Alex Deucher <alexander.deucher@xxxxxxx> > + * which is only used for the above case. Everything else uses > + * the normal commit function, which ensures that we never steal > + * the display from an active drm master. > + */ > + force = var->activate & FB_ACTIVATE_KD_TEXT; > + > + __drm_fb_helper_restore_fbdev_mode_unlocked(fb_helper, force); > > return 0; > } > diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c > index 9d28a8e3328f..e2a490c5ae08 100644 > --- a/drivers/video/fbdev/core/fbcon.c > +++ b/drivers/video/fbdev/core/fbcon.c > @@ -2402,7 +2402,8 @@ static int fbcon_blank(struct vc_data *vc, int blank, int mode_switch) > ops->graphics = 1; > > if (!blank) { > - var.activate = FB_ACTIVATE_NOW | FB_ACTIVATE_FORCE; > + var.activate = FB_ACTIVATE_NOW | FB_ACTIVATE_FORCE | > + FB_ACTIVATE_KD_TEXT; > fb_set_var(info, &var); > ops->graphics = 0; > ops->var = info->var; > diff --git a/include/uapi/linux/fb.h b/include/uapi/linux/fb.h > index b6aac7ee1f67..4c14e8be7267 100644 > --- a/include/uapi/linux/fb.h > +++ b/include/uapi/linux/fb.h > @@ -205,6 +205,7 @@ struct fb_bitfield { > #define FB_ACTIVATE_ALL 64 /* change all VCs on this fb */ > #define FB_ACTIVATE_FORCE 128 /* force apply even when no change*/ > #define FB_ACTIVATE_INV_MODE 256 /* invalidate videomode */ > +#define FB_ACTIVATE_KD_TEXT 512 /* for KDSET vt ioctl */ > > #define FB_ACCELF_TEXT 1 /* (OBSOLETE) see fb_info.flags and vc_mode */ > > -- > 2.27.0 > > _______________________________________________ > dri-devel mailing list > dri-devel@xxxxxxxxxxxxxxxxxxxxx > https://lists.freedesktop.org/mailman/listinfo/dri-devel
