Re: [PATCH v3 5/5] drm/vkms: Implement CRC debugfs API

[Sean Paul <seanpaul@chromium.org>]

On Thu, Jul 19, 2018 at 03:22:16AM +0300, Haneen Mohammed wrote:
> Implement the set_crc_source() callback.
> Compute CRC using crc32 on the visible part of the framebuffer.
> Use ordered workqueue 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 and atomic_flush to wrap the event
> handling code completely and match the flip event with the CRC.
> 
> Signed-off-by: Haneen Mohammed <hamohammed.sa@gmail.com>
> ---
> Changes in v3:
> - flush work item instead of workqueue
> - include missing vkms_crc.c file
> 
>  drivers/gpu/drm/vkms/Makefile     |  2 +-
>  drivers/gpu/drm/vkms/vkms_crc.c   | 66 +++++++++++++++++++++++++++++++
>  drivers/gpu/drm/vkms/vkms_crtc.c  | 58 ++++++++++++++++++++++-----
>  drivers/gpu/drm/vkms/vkms_drv.c   |  1 +
>  drivers/gpu/drm/vkms/vkms_drv.h   | 21 ++++++++++
>  drivers/gpu/drm/vkms/vkms_plane.c | 10 +++++
>  6 files changed, 148 insertions(+), 10 deletions(-)
>  create mode 100644 drivers/gpu/drm/vkms/vkms_crc.c
> 
> diff --git a/drivers/gpu/drm/vkms/Makefile b/drivers/gpu/drm/vkms/Makefile
> index 986297da51bf..37966914f70b 100644
> --- a/drivers/gpu/drm/vkms/Makefile
> +++ b/drivers/gpu/drm/vkms/Makefile
> @@ -1,3 +1,3 @@
> -vkms-y := vkms_drv.o vkms_plane.o vkms_output.o vkms_crtc.o vkms_gem.o
> +vkms-y := vkms_drv.o vkms_plane.o vkms_output.o vkms_crtc.o vkms_gem.o vkms_crc.o
>  
>  obj-$(CONFIG_DRM_VKMS) += vkms.o
> diff --git a/drivers/gpu/drm/vkms/vkms_crc.c b/drivers/gpu/drm/vkms/vkms_crc.c
> new file mode 100644
> index 000000000000..9e8bb5c7fc80
> --- /dev/null
> +++ b/drivers/gpu/drm/vkms/vkms_crc.c
> @@ -0,0 +1,66 @@
> +// SPDX-License-Identifier: GPL-2.0
> +#include "vkms_drv.h"
> +#include <linux/crc32.h>
> +#include <drm/drm_gem_framebuffer_helper.h>
> +
> +static uint32_t _vkms_get_crc(struct vkms_crc_data *crc_data)
> +{
> +	struct drm_framebuffer *fb = &crc_data->fb;
> +	struct drm_gem_object *gem_obj = drm_gem_fb_get_obj(fb, 0);
> +	struct vkms_gem_object *vkms_obj = drm_gem_to_vkms_gem(gem_obj);
> +	u32 crc = 0;
> +	int i = 0;
> +	unsigned int x = crc_data->src.x1 >> 16;
> +	unsigned int y = crc_data->src.y1 >> 16;
> +	unsigned int height = drm_rect_height(&crc_data->src) >> 16;
> +	unsigned int width = drm_rect_width(&crc_data->src) >> 16;
> +	unsigned int cpp = fb->format->cpp[0];
> +	unsigned int src_offset;
> +	unsigned int size_byte = width * cpp;
> +	void *vaddr = vkms_obj->vaddr;

You should hold the lock when copying the data from crc_data.

> +
> +	if (WARN_ON(!vaddr))
> +		return crc;
> +
> +	for (i = y; i < y + height; i++) {
> +		src_offset = fb->offsets[0] + (i * fb->pitches[0]) + (x * cpp);
> +		crc = crc32_le(crc, vaddr + src_offset, size_byte);
> +	}
> +
> +	return crc;
> +}
> +
> +void vkms_crc_work_handle(struct work_struct *work)
> +{
> +	struct vkms_crtc_state *crtc_state = container_of(work,
> +						struct vkms_crtc_state,
> +						crc_work);
> +	struct drm_crtc *crtc = crtc_state->base.crtc;
> +	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
> +
> +	if (crtc_state && out->crc_enabled) {
> +		u32 crc32 = _vkms_get_crc(&crtc_state->data);
> +		unsigned int n_frame = crtc_state->n_frame;
> +
> +		drm_crtc_add_crc_entry(crtc, true, n_frame, &crc32);
> +	}
> +}
> +
> +int vkms_set_crc_source(struct drm_crtc *crtc, const char *src_name,
> +			size_t *values_cnt)
> +{
> +	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
> +

You should hold the lock when changing this value.

> +	if (!src_name) {
> +		out->crc_enabled = false;
> +	} else if (strcmp(src_name, "auto") == 0) {
> +		out->crc_enabled = true;
> +	} else {
> +		out->crc_enabled = false;
> +		return -EINVAL;
> +	}
> +
> +	*values_cnt = 1;
> +
> +	return 0;
> +}
> diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
> index 26babb85ca77..a7b39627b581 100644
> --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> @@ -10,17 +10,32 @@
>  #include <drm/drm_atomic_helper.h>
>  #include <drm/drm_crtc_helper.h>
>  
> -static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
> +static void _vblank_handle(struct vkms_output *output)
>  {
> -	struct vkms_output *output = container_of(timer, struct vkms_output,
> -						  vblank_hrtimer);
>  	struct drm_crtc *crtc = &output->crtc;
> -	int ret_overrun;
> +	struct vkms_crtc_state *state = to_vkms_crtc_state(crtc->state);
>  	bool ret;
>  
> +	spin_lock(&output->lock);
>  	ret = drm_crtc_handle_vblank(crtc);
>  	if (!ret)
> -		DRM_ERROR("vkms failure on handling vblank");
> +		DRM_ERROR("vkms failure on handling vblank\n");
> +
> +	if (state && output->crc_enabled) {
> +		state->n_frame = drm_crtc_accurate_vblank_count(crtc);
> +		queue_work(output->crc_workq, &state->crc_work);
> +	}
> +
> +	spin_unlock(&output->lock);
> +}
> +
> +static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
> +{
> +	struct vkms_output *output = container_of(timer, struct vkms_output,
> +						  vblank_hrtimer);
> +	int ret_overrun;
> +
> +	_vblank_handle(output);
>  
>  	ret_overrun = hrtimer_forward_now(&output->vblank_hrtimer,
>  					  output->period_ns);
> @@ -97,6 +112,8 @@ vkms_atomic_crtc_duplicate_state(struct drm_crtc *crtc)
>  
>  	__drm_atomic_helper_crtc_duplicate_state(crtc, &vkms_state->base);
>  
> +	INIT_WORK(&vkms_state->crc_work, vkms_crc_work_handle);
> +
>  	return &vkms_state->base;
>  }
>  
> @@ -108,7 +125,13 @@ static void vkms_atomic_crtc_destroy_state(struct drm_crtc *crtc,
>  	vkms_state = to_vkms_crtc_state(state);
>  
>  	__drm_atomic_helper_crtc_destroy_state(state);
> -	kfree(vkms_state);
> +
> +	if (vkms_state) {
> +		flush_work(&vkms_state->crc_work);
> +		drm_framebuffer_put(&vkms_state->data.fb);

It'd be nice to leave a breadcrumb explaining where this reference is acquired.
ie: /* dropping the reference we acquired in vkms_primary_plane_update() */

> +		memset(&vkms_state->data, 0, sizeof(struct vkms_crc_data));
> +		kfree(vkms_state);
> +	}
>  }
>  
>  static const struct drm_crtc_funcs vkms_crtc_funcs = {
> @@ -120,6 +143,7 @@ static const struct drm_crtc_funcs vkms_crtc_funcs = {
>  	.atomic_destroy_state   = vkms_atomic_crtc_destroy_state,
>  	.enable_vblank		= vkms_enable_vblank,
>  	.disable_vblank		= vkms_disable_vblank,
> +	.set_crc_source		= vkms_set_crc_source,
>  };
>  
>  static void vkms_crtc_atomic_enable(struct drm_crtc *crtc,
> @@ -134,26 +158,37 @@ static void vkms_crtc_atomic_disable(struct drm_crtc *crtc,
>  	drm_crtc_vblank_off(crtc);
>  }
>  
> +static void vkms_crtc_atomic_begin(struct drm_crtc *crtc,
> +				   struct drm_crtc_state *old_crtc_state)
> +{
> +	struct vkms_output *vkms_output = drm_crtc_to_vkms_output(crtc);
> +
> +	spin_lock_irq(&vkms_output->lock);

Can you please add a comment explaining that we're holding this across the
commit to block the vblank timer, and why.

> +}
> +
>  static void vkms_crtc_atomic_flush(struct drm_crtc *crtc,
>  				   struct drm_crtc_state *old_crtc_state)
>  {
> -	unsigned long flags;
> +	struct vkms_output *vkms_output = drm_crtc_to_vkms_output(crtc);
>  
>  	if (crtc->state->event) {
> -		spin_lock_irqsave(&crtc->dev->event_lock, flags);
> +		spin_lock(&crtc->dev->event_lock);

Either don't change this (since it's always safe to call _irqsave), or add a
comment explaining why you don't need to.

>  
>  		if (drm_crtc_vblank_get(crtc) != 0)
>  			drm_crtc_send_vblank_event(crtc, crtc->state->event);
>  		else
>  			drm_crtc_arm_vblank_event(crtc, crtc->state->event);
>  
> -		spin_unlock_irqrestore(&crtc->dev->event_lock, flags);
> +		spin_unlock(&crtc->dev->event_lock);
>  
>  		crtc->state->event = NULL;
>  	}
> +
> +	spin_unlock_irq(&vkms_output->lock);
>  }
>  
>  static const struct drm_crtc_helper_funcs vkms_crtc_helper_funcs = {
> +	.atomic_begin	= vkms_crtc_atomic_begin,
>  	.atomic_flush	= vkms_crtc_atomic_flush,
>  	.atomic_enable	= vkms_crtc_atomic_enable,
>  	.atomic_disable	= vkms_crtc_atomic_disable,
> @@ -162,6 +197,7 @@ static const struct drm_crtc_helper_funcs vkms_crtc_helper_funcs = {
>  int vkms_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
>  		   struct drm_plane *primary, struct drm_plane *cursor)
>  {
> +	struct vkms_output *vkms_out = drm_crtc_to_vkms_output(crtc);
>  	int ret;
>  
>  	ret = drm_crtc_init_with_planes(dev, crtc, primary, cursor,
> @@ -173,5 +209,9 @@ int vkms_crtc_init(struct drm_device *dev, struct drm_crtc *crtc,
>  
>  	drm_crtc_helper_add(crtc, &vkms_crtc_helper_funcs);
>  
> +	spin_lock_init(&vkms_out->lock);
> +
> +	vkms_out->crc_workq = alloc_ordered_workqueue("vkms_crc_workq", 0);
> +
>  	return ret;
>  }
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.c b/drivers/gpu/drm/vkms/vkms_drv.c
> index 37aa2ef33b21..5d78bd97e69c 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.c
> +++ b/drivers/gpu/drm/vkms/vkms_drv.c
> @@ -46,6 +46,7 @@ static void vkms_release(struct drm_device *dev)
>  	platform_device_unregister(vkms->platform);
>  	drm_mode_config_cleanup(&vkms->drm);
>  	drm_dev_fini(&vkms->drm);
> +	destroy_workqueue(vkms->output.crc_workq);
>  }
>  
>  static struct drm_driver vkms_driver = {
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index 75e52d61e65d..a80281a12010 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -20,12 +20,23 @@ static const u32 vkms_formats[] = {
>  	DRM_FORMAT_XRGB8888,
>  };
>  
> +struct vkms_crc_data {
> +	struct drm_rect src;
> +	struct drm_framebuffer fb;
> +};
> +
>  /**
>   * vkms_crtc_state - Driver specific CRTC state
>   * @base: base CRTC state
> + * @crc_work: work struct to compute and add CRC entries
> + * @data: data required for CRC computation
> + * @n_frame: frame number for computed CRC
>   */
>  struct vkms_crtc_state {
>  	struct drm_crtc_state base;
> +	struct work_struct crc_work;
> +	struct vkms_crc_data data;
> +	unsigned int n_frame;
>  };
>  
>  struct vkms_output {
> @@ -35,6 +46,11 @@ struct vkms_output {
>  	struct hrtimer vblank_hrtimer;
>  	ktime_t period_ns;
>  	struct drm_pending_vblank_event *event;
> +	bool crc_enabled;
> +	/* ordered wq for crc_work */
> +	struct workqueue_struct *crc_workq;
> +	/* protects concurrent access to crc_data */
> +	spinlock_t lock;
>  };
>  
>  struct vkms_device {
> @@ -95,4 +111,9 @@ int vkms_gem_vmap(struct drm_gem_object *obj);
>  
>  void vkms_gem_vunmap(struct drm_gem_object *obj);
>  
> +/* CRC Support */
> +int vkms_set_crc_source(struct drm_crtc *crtc, const char *src_name,
> +			size_t *values_cnt);
> +void vkms_crc_work_handle(struct work_struct *work);
> +
>  #endif /* _VKMS_DRV_H_ */
> diff --git a/drivers/gpu/drm/vkms/vkms_plane.c b/drivers/gpu/drm/vkms/vkms_plane.c
> index 5b7c5d59f103..b316b2af88ee 100644
> --- a/drivers/gpu/drm/vkms/vkms_plane.c
> +++ b/drivers/gpu/drm/vkms/vkms_plane.c
> @@ -24,6 +24,16 @@ static const struct drm_plane_funcs vkms_plane_funcs = {
>  static void vkms_primary_plane_update(struct drm_plane *plane,
>  				      struct drm_plane_state *old_state)
>  {
> +	struct vkms_crtc_state *state;
> +
> +	if (!plane->state->crtc || !plane->state->fb)
> +		return;
> +
> +	state = to_vkms_crtc_state(plane->state->crtc->state);
> +	memcpy(&state->data.src, &plane->state->src, sizeof(struct drm_rect));
> +	memcpy(&state->data.fb, plane->state->fb,
> +	       sizeof(struct drm_framebuffer));
> +	drm_framebuffer_get(&state->data.fb);

Similarly to above, a comment explaining this is released in state_destroy would
be helpful.

>  }
>  
>  static int vkms_plane_atomic_check(struct drm_plane *plane,
> -- 
> 2.17.1
> 

-- 
Sean Paul, Software Engineer, Google / Chromium OS
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