diff options
Diffstat (limited to 'drivers/gpu/drm/drm_irq.c')
| -rw-r--r-- | drivers/gpu/drm/drm_irq.c | 40 |
1 files changed, 34 insertions, 6 deletions
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c index c0c3f2006203..b969a64a1514 100644 --- a/drivers/gpu/drm/drm_irq.c +++ b/drivers/gpu/drm/drm_irq.c @@ -713,10 +713,10 @@ EXPORT_SYMBOL(drm_calc_timestamping_constants); * Negative value on error, failure or if not supported in current * video mode: * - * -EINVAL - Invalid CRTC. - * -EAGAIN - Temporary unavailable, e.g., called before initial modeset. - * -ENOTSUPP - Function not supported in current display mode. - * -EIO - Failed, e.g., due to failed scanout position query. + * -EINVAL Invalid CRTC. + * -EAGAIN Temporary unavailable, e.g., called before initial modeset. + * -ENOTSUPP Function not supported in current display mode. + * -EIO Failed, e.g., due to failed scanout position query. * * Returns or'ed positive status flags on success: * @@ -1008,6 +1008,31 @@ static void send_vblank_event(struct drm_device *dev, * period. This helper function implements exactly the required vblank arming * behaviour. * + * NOTE: Drivers using this to send out the event in struct &drm_crtc_state + * as part of an atomic commit must ensure that the next vblank happens at + * exactly the same time as the atomic commit is committed to the hardware. This + * function itself does **not** protect again the next vblank interrupt racing + * with either this function call or the atomic commit operation. A possible + * sequence could be: + * + * 1. Driver commits new hardware state into vblank-synchronized registers. + * 2. A vblank happens, committing the hardware state. Also the corresponding + * vblank interrupt is fired off and fully processed by the interrupt + * handler. + * 3. The atomic commit operation proceeds to call drm_crtc_arm_vblank_event(). + * 4. The event is only send out for the next vblank, which is wrong. + * + * An equivalent race can happen when the driver calls + * drm_crtc_arm_vblank_event() before writing out the new hardware state. + * + * The only way to make this work safely is to prevent the vblank from firing + * (and the hardware from committing anything else) until the entire atomic + * commit sequence has run to completion. If the hardware does not have such a + * feature (e.g. using a "go" bit), then it is unsafe to use this functions. + * Instead drivers need to manually send out the event from their interrupt + * handler by calling drm_crtc_send_vblank_event() and make sure that there's no + * possible race with the hardware committing the atomic update. + * * Caller must hold event lock. Caller must also hold a vblank reference for * the event @e, which will be dropped when the next vblank arrives. */ @@ -1030,8 +1055,11 @@ EXPORT_SYMBOL(drm_crtc_arm_vblank_event); * @crtc: the source CRTC of the vblank event * @e: the event to send * - * Updates sequence # and timestamp on event, and sends it to userspace. - * Caller must hold event lock. + * Updates sequence # and timestamp on event for the most recently processed + * vblank, and sends it to userspace. Caller must hold event lock. + * + * See drm_crtc_arm_vblank_event() for a helper which can be used in certain + * situation, especially to send out events for atomic commit operations. */ void drm_crtc_send_vblank_event(struct drm_crtc *crtc, struct drm_pending_vblank_event *e) |
