framedur_ns = 3152 * 2148 * 1000000 / 406 = 16675852216 ns (~16.7 s)
16675852216 does not fit into an int and wraps to roughly -504000000.
ns_to_ktime() then yields a negative interval and the timer stops working.
Found by bisection, which pointed at commit a036f5fceedb ("drm/virtgpu:
Use vblank timer"). That commit merely made virtio-gpu use the vblank
timer and thereby exposed the pre-existing problem in the timer setup
added by commit 74afeb812850 ("drm/vblank: Add vblank timer").
To fix this, modify drm_calc_timestamping_constants() to use u64 for
calculations, check for INT_MAX overflows, and return an error code.
drm_crtc_vblank_start_timer() will then propagate the error, enabling
the driver to fall back to immediate vblank events. Valid modes are
unaffected, and the timer self-heals on the next mode with a sane clock.
v4:
- avoid log spamming with drm_warn_once()
Fixes: 74afeb812850 ("drm/vblank: Add vblank timer")
Suggested-by: Thomas Zimmermann <[email protected]>
Signed-off-by: Roman Ilin <[email protected]>
---
I took Roman's patch from [1] and replaced the error messages with
warn_once, as suggestde in my review.
[1] https://lore.kernel.org/dri-devel/[email protected]/
---
drivers/gpu/drm/drm_vblank.c | 73 +++++++++++++++++++++++-------------
include/drm/drm_vblank.h | 4 +-
2 files changed, 49 insertions(+), 28 deletions(-)
diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index f90fb2d13e42..72b543bca9e3 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c
@@ -631,45 +631,54 @@ EXPORT_SYMBOL(drm_crtc_vblank_waitqueue);
* drm_crtc_vblank_helper_get_vblank_timestamp(). They are derived from
* CRTC's true scanout timing, so they take things like panel scaling or
* other adjustments into account.
+ *
+ * Returns:
+ * 0 on success, or a negative errno code otherwise.
*/
-void drm_calc_timestamping_constants(struct drm_crtc *crtc,
- const struct drm_display_mode *mode)
+int drm_calc_timestamping_constants(struct drm_crtc *crtc,
+ const struct drm_display_mode *mode)
{
struct drm_device *dev = crtc->dev;
unsigned int pipe = drm_crtc_index(crtc);
struct drm_vblank_crtc *vblank = drm_crtc_vblank_crtc(crtc);
- int linedur_ns = 0, framedur_ns = 0;
+ u64 linedur_ns, framedur_ns;
int dotclock = mode->crtc_clock;
+ unsigned int frame_size;
if (!drm_dev_has_vblank(dev))
- return;
+ return 0;
if (drm_WARN_ON(dev, pipe >= dev->num_crtcs))
- return;
+ return -EINVAL;
- /* Valid dotclock? */
- if (dotclock > 0) {
- int frame_size = mode->crtc_htotal * mode->crtc_vtotal;
+ if (dotclock <= 0) {
+ drm_err_once(dev, "crtc %u: Can't calculate constants, dotclock =
%d!\n",
+ crtc->base.id, dotclock);
+ goto error;
+ }
- /*
- * Convert scanline length in pixels and video
- * dot clock to line duration and frame duration
- * in nanoseconds:
- */
- linedur_ns = div_u64((u64) mode->crtc_htotal * 1000000,
dotclock);
- framedur_ns = div_u64((u64) frame_size * 1000000, dotclock);
+ frame_size = (unsigned int)mode->crtc_htotal * (unsigned
int)mode->crtc_vtotal;
- /*
- * Fields of interlaced scanout modes are only half a frame
duration.
- */
- if (mode->flags & DRM_MODE_FLAG_INTERLACE)
- framedur_ns /= 2;
- } else {
- drm_err(dev, "crtc %u: Can't calculate constants, dotclock =
0!\n",
- crtc->base.id);
+ /*
+ * Convert scanline length in pixels and video dot clock to line
duration
+ * and frame duration in nanoseconds.
+ */
+ linedur_ns = div_u64((u64)mode->crtc_htotal * 1000000, dotclock);
+ framedur_ns = div_u64((u64)frame_size * 1000000, dotclock);
+
+ /*
+ * Fields of interlaced scanout modes are only half a frame duration.
+ */
+ if (mode->flags & DRM_MODE_FLAG_INTERLACE)
+ framedur_ns /= 2;
+
+ if (linedur_ns > INT_MAX || framedur_ns > INT_MAX) {
+ drm_err_once(dev, "crtc %u: Can't calculate constants, mode clock
too small!\n",
+ crtc->base.id);
+ goto error;
}
- vblank->linedur_ns = linedur_ns;
+ vblank->linedur_ns = linedur_ns;
vblank->framedur_ns = framedur_ns;
drm_mode_copy(&vblank->hwmode, mode);
@@ -678,7 +687,16 @@ void drm_calc_timestamping_constants(struct drm_crtc *crtc,
crtc->base.id, mode->crtc_htotal,
mode->crtc_vtotal, mode->crtc_vdisplay);
drm_dbg_core(dev, "crtc %u: clock %d kHz framedur %d linedur %d\n",
- crtc->base.id, dotclock, framedur_ns, linedur_ns);
+ crtc->base.id, dotclock,
+ vblank->framedur_ns, vblank->linedur_ns);
+
+ return 0;
+
+error:
+ vblank->linedur_ns = 0;
+ vblank->framedur_ns = 0;
+ drm_mode_copy(&vblank->hwmode, mode);
+ return -EINVAL;
}
EXPORT_SYMBOL(drm_calc_timestamping_constants);
@@ -2221,6 +2239,7 @@ int drm_crtc_vblank_start_timer(struct drm_crtc *crtc)
struct drm_vblank_crtc *vblank = drm_crtc_vblank_crtc(crtc);
struct drm_vblank_crtc_timer *vtimer = &vblank->vblank_timer;
unsigned long flags;
+ int ret;
if (!vtimer->crtc) {
/*
@@ -2239,7 +2258,9 @@ int drm_crtc_vblank_start_timer(struct drm_crtc *crtc)
hrtimer_try_to_cancel(&vtimer->timer);
}
- drm_calc_timestamping_constants(crtc, &crtc->mode);
+ ret = drm_calc_timestamping_constants(crtc, &crtc->mode);
+ if (ret)
+ return ret;
spin_lock_irqsave(&vtimer->interval_lock, flags);
vtimer->interval = ns_to_ktime(vblank->framedur_ns);
diff --git a/include/drm/drm_vblank.h b/include/drm/drm_vblank.h
index 2fcef9c0f5b1..d99772dfa034 100644
--- a/include/drm/drm_vblank.h
+++ b/include/drm/drm_vblank.h
@@ -311,8 +311,8 @@ void drm_crtc_vblank_on(struct drm_crtc *crtc);
u64 drm_crtc_accurate_vblank_count(struct drm_crtc *crtc);
void drm_crtc_vblank_restore(struct drm_crtc *crtc);
-void drm_calc_timestamping_constants(struct drm_crtc *crtc,
- const struct drm_display_mode *mode);
+int drm_calc_timestamping_constants(struct drm_crtc *crtc,
+ const struct drm_display_mode *mode);
wait_queue_head_t *drm_crtc_vblank_waitqueue(struct drm_crtc *crtc);
void drm_crtc_set_max_vblank_count(struct drm_crtc *crtc,
u32 max_vblank_count);
base-commit: 06576c2b43750d990297b8ff1989b94ac72e855f
prerequisite-patch-id: 6729bb10d5e338678e78ccda2dd24f232a13cd22
prerequisite-patch-id: 9d94d20bd45967493b4dc339b58082e1c8da0f4f
prerequisite-patch-id: 6ac8d22df34db9e7d467b1ab95ad30f94841d5db
prerequisite-patch-id: f548dbde3f944ca3415c808be628719acebe898a
prerequisite-patch-id: 2ae91ee8e2bbcd33b8325be046e7214185aba6aa
prerequisite-patch-id: f97bbde08a9996d7c62ca3e3ebfcd387e50bc5c3
prerequisite-patch-id: ecc3c825277bc9978c6979455517249a074c0cb1
prerequisite-patch-id: 0449925cca36664b566f614bfb7d573a11f0575f
prerequisite-patch-id: 9fb2c2787244e9621847af09bea03e575e6276c7
prerequisite-patch-id: eb4384d581805e1178d22e7df45f134223c38305
prerequisite-patch-id: 1a7a529e4b2864abe8071aa44598d28ce72483f4
prerequisite-patch-id: 844a85f4c2fe2f72209b82d46614004c3cfe4123
prerequisite-patch-id: 13f7cb22114c648d35f8c9fa74e9165656ce31eb
prerequisite-patch-id: 20ee46bd6fdd91e39f71d22f52ef6682a4e41512
prerequisite-patch-id: 1d26c0ff91796ff1e62d3831d00bee18723788ef
prerequisite-patch-id: 007f6ea0d09bef54b689bae0eb5abeb497bdfaad
prerequisite-patch-id: 2d89c1507c909520adf9bfb1a137d458a819ae8f
prerequisite-patch-id: d90dc4134468870ab8ccbd71547c9552dff74fbd
prerequisite-patch-id: c67e5d886a47b7d0266d81100837557fda34cb24
prerequisite-patch-id: a5a973e527c88a5b47053d7a72aefe0b550197cb
prerequisite-patch-id: b9adc9622920a3e70168e672c2c92795b3e3a106
prerequisite-patch-id: 5030de433a01c2e99056cadb676a8e2ba35f055a
--
2.55.0
