The crc computation worker needs to be able to get at some data
structures and framebuffer mappings, while potentially more atomic
updates are going on. The solution thus far is to copy relevant bits
around, but that's very tedious.
Here's a new approach, which tries to be more clever, but relies on a
few not-so-obvious things:
- crtc_state is always updated when a plane_state changes. Therefore
we can just stuff plane_state pointers into a crtc_state. That
solves the problem of easily getting at the needed plane_states.
- with the flushing changes from previous patches the above also holds
without races due to the next atomic update being a bit eager with
cleaning up pending work - we always wait for all crc work items to
complete before unmapping framebuffers.
- we also need to make sure that the hrtimer fires off the right
worker. Keep a new distinct crc_state pointer, under the
vkms_output->lock protection for this. Note that crtc->state is
updated very early in the atomic commit, way before we arm the
vblank event - the vblank event should always match the buffers we
use to compute the crc. This also solves an issue in the hrtimer,
where we've accessed drm_crtc->state without holding the right locks
(we held none - oops).
- in the worker itself we can then just access the plane states we
need, again solving a bunch of ordering and locking issues.
Accessing plane->state requires locks, accessing the private
vkms_crtc_state->active_planes pointer only requires that the memory
doesn't get freed too early.
The idea behind vkms_crtc_state->active_planes is that this would
contain all visible planes, in z-order, as a first step towards a more
generic blending implementation.
Note that this patch also fixes races between prepare_fb/cleanup_fb
and the crc worker accessing ->vaddr.
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Tested-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190606222751.32567-10-daniel.vetter@ffwll.ch
The issue we have is that the crc worker might fall behind. We've
tried to handle this by tracking both the earliest frame for which it
still needs to compute a crc, and the last one. Plus when the
crtc_state changes, we have a new work item, which are all run in
order due to the ordered workqueue we allocate for each vkms crtc.
Trouble is there's been a few small issues in the current code:
- we need to capture frame_end in the vblank hrtimer, not in the
worker. The worker might run much later, and then we generate a lot
of crc for which there's already a different worker queued up.
- frame number might be 0, so create a new crc_pending boolean to
track this without confusion.
- we need to atomically grab frame_start/end and clear it, so do that
all in one go. This is not going to create a new race, because if we
race with the hrtimer then our work will be re-run.
- only race that can happen is the following:
1. worker starts
2. hrtimer runs and updates frame_end
3. worker grabs frame_start/end, already reading the new frame_end,
and clears crc_pending
4. hrtimer calls queue_work()
5. worker completes
6. worker gets re-run, crc_pending is false
Explain this case a bit better by rewording the comment.
v2: Demote warning level output to debug when we fail to requeue, this
is expected under high load when the crc worker can't quite keep up.
Cc: Shayenne Moura <shayenneluzmoura@gmail.com>
Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Tested-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190606222751.32567-2-daniel.vetter@ffwll.ch
crtc_state is accessed by both vblank_handle() and the ordered
work_struct handle vkms_crc_work_handle() to retrieve and or update
the frame number for computed CRC.
Since work_struct can fail, add frame_end to account for missing frame
numbers.
Use (frame_[start/end]) for synchronization between hrtimer callback
and ordered work_struct handle.
This patch passes the following subtests from igt kms_pipe_crc_basic test:
bad-source, read-crc-pipe-A, read-crc-pipe-A-frame-sequence,
nonblocking-crc-pipe-A, nonblocking-crc-pipe-A-frame-sequence
Signed-off-by: Haneen Mohammed <hamohammed.sa@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20180903211743.GA2773@haneenDRM
This patch implement the necessary functions to compute and add CRCs
entries:
- Implement the set_crc_source() callback.
- Compute CRC using crc32 on the visible part of the framebuffer.
- Use ordered workqueue per output to compute and add CRC at the end
of a vblank.
- Use appropriate synchronization methods since the CRC computation must
be atomic wrt the generated vblank event for a given atomic update, by
using spinlock across atomic_begin/atomic_flush to wrap the event
handling code completely and match the flip event with the CRC.
Since vkms_crc_work_handle() can sleep, spinlock can't be acquired
while accessing vkms_output->primary_crc to compute CRC.
To make sure the data is updated and released without conflict with
the vkms_crc_work_handle(), the work_struct is flushed @crtc_destroy
and the data is updated before scheduling the work handle again, as
follow:
* CRC data update:
1- store vkms_crc_data {fb, src} per plane_state
2- @plane_duplicate_state -> allocate vkms_crc_data
3- during atomic commit (@atomic_update) ->
a) copy {fb, src} to plane_state->crc_data
b) get reference to fb,
3- @plane_destroy_state -> a) if (fb refcount) remove reference to fb
b) deallocate crc_data
* Atomic Commit:
1- vkms_plane_atomic_check
2- vkms_prepare_fb -> vmap vkms_gem_obj->vaddr
3- atomic_begin -> hold crc spinlock
4- atomic_plane_update -> a) update vkms_output->primary_crc
b) get reference to fb
5- atomic_flush -> a) send vblank event while holding event_lock
b) release crc spinlock
* hrtimer regular callback:
1- hold crc spinlock
2- drm_crtc_handle_vblank()
3- queue vkms_crc_work_handle
4- release crc spinlock
* cleanup:
1- @cleanup_fb ->vunmap vkms_gem_obj->vaddr
2- @crtc_destroy -> flush work struct
3- @plane_destroy -> a) if (fb refcount) remove reference to fb
b) deallocate crc_data
Signed-off-by: Haneen Mohammed <hamohammed.sa@gmail.com>
[seanpaul fixed typo in vkms_crtc s/vblamk/vblank/]
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/b948327f48c3e70ab232b4a0848ee6d033b26484.1533171495.git.hamohammed.sa@gmail.com
This commit adds regular vblank events simulated through hrtimers, which
is a feature required by VKMS to mimic real hardware. Additionally, all
the vblank event send after pageflip is kept in the atomic_flush
function.
Changes since V1:
- Compute the vblank timer interval per interruption
Ville Syrjälä and Daniel Vetter:
- Removes hardcoded vblank interval to get it from user space
Changes since V2:
Chris Wilson
- Removes unnecessary algorithm to compute the next period
Daniel Vetter:
- Uses drm_calc_timestamping_constants to get the vblank interval
instead of calculating it manually
- Adds disable_vblank helper that turns of crtc
- Simplifies implementation by using drm_crtc_arm_vblank_event
- Replaces the code in atomic_begin to atomic_flush
- Removes unnecessary field in vkms_output
Changes since V3:
Daniel Vetter:
- Squash "drm/vkms: Add atomic helpers functions" into the commit that
handling vblank events simulated by hrtimers
Signed-off-by: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/7709bba40782ec06332d57fff337797b272581fc.1531359228.git.rodrigosiqueiramelo@gmail.com
