On Thu, Jul 05, 2018 at 12:48:43AM -0300, Rodrigo Siqueira wrote:
> This commit adds regular vblank events simulated through hrtimers, which
> is a feature required by VKMS to mimic real hardware. Notice that
> keeping the periodicity as close as possible to the one specified in
> user space represents a vital constraint. In this sense, the callback
> function implements an algorithm based on module operations that avoids
> the accumulation of errors.
>
> Assuming we begin operating at timestamp 0, every event should happen at
> timestamps that are multiples of the requested period, i.e.,
> current_timestamp % period == 0. Since we do *not* generally start at
> timestamp 0, we calculate the modulus of this initial timestamp and try
> to make all following events happen when current_timestamp % period ==
> initial_timestamp % period (variables “current_offset” and
> “base_offset”). We do this by measuring the difference between them at
> each iteration and adjusting the next waiting period accordingly.
>
> Signed-off-by: Rodrigo Siqueira <rodrigosiqueiram...@gmail.com>
Looks good. I've done a detailed review and found a bunch of things to
polish.
When resending patches please include a short summary of the changes
you've done. This helps reviewers a lot. E.g. for this one here:
Changes since v1:
- Compute the timer interval using the mode.
For the next revision you keep that and add
Changes since v2:
- Use the timing information already computed by core code.
- Use absolute timer mode
- and-so-on ...
Cheers, Daniel
> ---
> drivers/gpu/drm/vkms/vkms_crtc.c | 99 +++++++++++++++++++++++++++++++-
> drivers/gpu/drm/vkms/vkms_drv.c | 9 +++
> drivers/gpu/drm/vkms/vkms_drv.h | 20 +++++++
> 3 files changed, 126 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c
> b/drivers/gpu/drm/vkms/vkms_crtc.c
> index 84cc05506b09..35d39d25df34 100644
> --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> @@ -10,6 +10,83 @@
> #include <drm/drm_atomic_helper.h>
> #include <drm/drm_crtc_helper.h>
>
> +static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
> +{
> + struct vkms_output *output = container_of(timer, struct vkms_output,
> + vblank_hrtimer);
> + struct drm_crtc *crtc = &output->crtc;
> + ktime_t new_period, current_timestamp, diff_times, current_offset,
> + candidate_expires;
> + unsigned long flags;
> + int ret_overrun;
> + bool ret;
> +
> + current_timestamp = ktime_get();
> + current_offset = current_timestamp % output->period_ns;
> + diff_times = ktime_sub(current_offset, output->base_offset);
> + candidate_expires = ktime_sub(current_timestamp, diff_times);
> + if (candidate_expires > output->expires)
> + output->expires = candidate_expires;
> +
> + ret = drm_crtc_handle_vblank(crtc);
> + if (!ret)
> + DRM_ERROR("vkms failure on handling vblank");
> +
> + if (output->event) {
You're accessing output->event without holding locks, that's not ok. But
see below, you can remove all that code.
> + spin_lock_irqsave(&crtc->dev->event_lock, flags);
> + drm_crtc_send_vblank_event(crtc, output->event);
> + output->event = NULL;
> + spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
> + drm_crtc_vblank_put(crtc);
> + }
> +
> + current_timestamp = ktime_get();
> + current_offset = current_timestamp % output->period_ns;
> + diff_times = ktime_sub(output->base_offset, current_offset);
> + new_period = ktime_add(output->period_ns, diff_times);
> + output->expires = ktime_add(current_timestamp, new_period);
> + ret_overrun = hrtimer_forward_now(&output->vblank_hrtimer, new_period);
> +
> + return HRTIMER_RESTART;
> +}
> +
> +static int vkms_enable_vblank(struct drm_crtc *crtc)
> +{
> + struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
> + unsigned long period = 1000 * crtc->mode.htotal * crtc->mode.vtotal /
> + crtc->mode.clock;
General note: Diving stuff in the kernel isn't easy, you need to use
division macros otherwise your code won't build on 32bit.
Wrt the calculation itself: That's already done for you in
drm_calc_timestamping_constants(), no need to reinvent that wheel.
> + ktime_t current_timestamp;
> +
> + hrtimer_init(&out->vblank_hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
Can't we use absolute timer mode here? That avoids all the timestampt
computations.
> + out->vblank_hrtimer.function = &vkms_vblank_simulate;
> + out->period_ns = ktime_set(0, period * US_TO_NS);
> + current_timestamp = ktime_get();
> + out->base_offset = current_timestamp % out->period_ns;
> + out->expires = ktime_add(current_timestamp, out->period_ns);
> + hrtimer_start(&out->vblank_hrtimer, out->period_ns, HRTIMER_MODE_REL);
> +
> + return 0;
> +}
> +
> +static void vkms_disable_vblank(struct drm_crtc *crtc)
> +{
> + struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
> +
> + hrtimer_cancel(&out->vblank_hrtimer);
> +}
> +
> +bool vkms_get_vblank_timestamp(struct drm_device *dev, unsigned int pipe,
> + int *max_error, ktime_t *vblank_time,
> + bool in_vblank_irq)
> +{
> + struct vkms_device *vkmsdev = drm_device_to_vkms_device(dev);
> + struct vkms_output *output = &vkmsdev->output;
> +
> + *vblank_time = output->expires;
> +
> + return true;
> +}
> +
> static const struct drm_crtc_funcs vkms_crtc_funcs = {
> .set_config = drm_atomic_helper_set_config,
> .destroy = drm_crtc_cleanup,
> @@ -17,6 +94,8 @@ static const struct drm_crtc_funcs vkms_crtc_funcs = {
> .reset = drm_atomic_helper_crtc_reset,
> .atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
> .atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
> + .enable_vblank = vkms_enable_vblank,
> + .disable_vblank = vkms_disable_vblank,
> };
>
> static int vkms_crtc_atomic_check(struct drm_crtc *crtc,
> @@ -28,11 +107,27 @@ static int vkms_crtc_atomic_check(struct drm_crtc *crtc,
> static void vkms_crtc_atomic_enable(struct drm_crtc *crtc,
> struct drm_crtc_state *old_state)
> {
> + drm_crtc_vblank_on(crtc);
drm_crtc_vblank_off is missing. That should result in some complaints when
you disable a crtc again ... Have you not seen any backtraces in dmesg?
> +}
> +
> +static void vkms_crtc_atomic_begin(struct drm_crtc *crtc,
> + struct drm_crtc_state *old_s)
> +{
> + struct vkms_output *vkms_output = drm_crtc_to_vkms_output(crtc);
> +
> + if (crtc->state->event) {
> + crtc->state->event->pipe = drm_crtc_index(crtc);
> + WARN_ON(drm_crtc_vblank_get(crtc) != 0);
> +
> + vkms_output->event = crtc->state->event;
You're missing locking here for output->event. Also I expect that you're
hitting the WARN_ON above (or you would, if you would call
drm_crtc_vblank_off).
Much simpler implementation is if you use drm_crtc_arm_vblank_event, plus
the fallback to sending the event out directly if the crtc is disabled.
See tegra_crtc_atomic_begin() for an example.
Also for the long-term plans we have with vkms with the crc stuff it's
better to put this all into the atomic_flush callback, not the
atomic_begin callback.
> + crtc->state->event = NULL;
> + }
> }
>
> static const struct drm_crtc_helper_funcs vkms_crtc_helper_funcs = {
> - .atomic_check = vkms_crtc_atomic_check,
> - .atomic_enable = vkms_crtc_atomic_enable,
> + .atomic_check = vkms_crtc_atomic_check,
> + .atomic_enable = vkms_crtc_atomic_enable,
> + .atomic_begin = vkms_crtc_atomic_begin,
> };
>
> int vkms_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
> index fe93f8c17997..6368048c6e54 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.c
> +++ b/drivers/gpu/drm/vkms/vkms_drv.c
> @@ -55,6 +55,7 @@ static struct drm_driver vkms_driver = {
> .dumb_create = vkms_dumb_create,
> .dumb_map_offset = vkms_dumb_map,
> .gem_vm_ops = &vkms_gem_vm_ops,
> + .get_vblank_timestamp = vkms_get_vblank_timestamp,
Ah, the last legacy hook where we don't yet have an option to use
drm_crtc_funcs instead. For now this is good here, but I think it'd be
great to do a follow-up task to clean this up, like we've already done
with the enable/disable_vblank hooks.
>
> .name = DRIVER_NAME,
> .desc = DRIVER_DESC,
> @@ -102,6 +103,14 @@ static int __init vkms_init(void)
> goto out_fini;
> }
>
> + vkms_device->drm.irq_enabled = true;
> +
> + ret = drm_vblank_init(&vkms_device->drm, 1);
> + if (ret) {
> + DRM_ERROR("Failed to vblank\n");
> + goto out_fini;
> + }
> +
> ret = vkms_modeset_init(vkms_device);
> if (ret)
> goto out_unregister;
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index 76f1720f81a5..b69a223bdfe6 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -5,6 +5,7 @@
> #include <drm/drm.h>
> #include <drm/drm_gem.h>
> #include <drm/drm_encoder.h>
> +#include <linux/hrtimer.h>
>
> #define XRES_MIN 32
> #define YRES_MIN 32
> @@ -15,6 +16,9 @@
> #define XRES_MAX 8192
> #define YRES_MAX 8192
>
> +#define DEFAULT_VBLANK_NS 16666666
> +#define US_TO_NS 1000
> +
> static const u32 vkms_formats[] = {
> DRM_FORMAT_XRGB8888,
> };
> @@ -23,6 +27,11 @@ struct vkms_output {
> struct drm_crtc crtc;
> struct drm_encoder encoder;
> struct drm_connector connector;
> + struct hrtimer vblank_hrtimer;
> + ktime_t period_ns;
> + ktime_t base_offset;
> + ktime_t expires;
> + struct drm_pending_vblank_event *event;
> };
>
> struct vkms_device {
> @@ -37,9 +46,20 @@ struct vkms_gem_object {
> struct page **pages;
> };
>
> +#define drm_crtc_to_vkms_output(target) \
> + container_of(target, struct vkms_output, crtc)
> +
> +#define drm_device_to_vkms_device(target) \
> + container_of(target, struct vkms_device, drm)
> +
> +/* CRTC */
> int vkms_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
> struct drm_plane *primary, struct drm_plane *cursor);
>
> +bool vkms_get_vblank_timestamp(struct drm_device *dev, unsigned int pipe,
> + int *max_error, ktime_t *vblank_time,
> + bool in_vblank_irq);
> +
> int vkms_output_init(struct vkms_device *vkmsdev);
>
> struct drm_plane *vkms_plane_init(struct vkms_device *vkmsdev);
> --
> 2.18.0
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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