[PATCH 03/10] drm/vkms: Rename vkms_output.state_lock to crc_lock

[Rodrigo Siqueira]

On Thu, Jun 6, 2019 at 7:28 PM Daniel Vetter <daniel.vetter at ffwll.ch> wrote:
>
> Plus add a comment about what it actually protects. It's very little.
>
> Signed-off-by: Daniel Vetter <daniel.vetter at intel.com>
> Cc: Rodrigo Siqueira <rodrigosiqueiramelo at gmail.com>
> Cc: Haneen Mohammed <hamohammed.sa at gmail.com>
> Cc: Daniel Vetter <daniel at ffwll.ch>
> ---
>  drivers/gpu/drm/vkms/vkms_crc.c  | 4 ++--
>  drivers/gpu/drm/vkms/vkms_crtc.c | 6 +++---
>  drivers/gpu/drm/vkms/vkms_drv.h  | 5 +++--
>  3 files changed, 8 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/vkms/vkms_crc.c b/drivers/gpu/drm/vkms/vkms_crc.c
> index 883e36fe7b6e..96806cd35ad4 100644
> --- a/drivers/gpu/drm/vkms/vkms_crc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crc.c
> @@ -168,14 +168,14 @@ void vkms_crc_work_handle(struct work_struct *work)
>         u64 frame_start, frame_end;
>         bool crc_pending;
>
> -       spin_lock_irq(&out->state_lock);
> +       spin_lock_irq(&out->crc_lock);
>         frame_start = crtc_state->frame_start;
>         frame_end = crtc_state->frame_end;
>         crc_pending = crtc_state->crc_pending;
>         crtc_state->frame_start = 0;
>         crtc_state->frame_end = 0;
>         crtc_state->crc_pending = false;
> -       spin_unlock_irq(&out->state_lock);
> +       spin_unlock_irq(&out->crc_lock);
>
>         /*
>          * We raced with the vblank hrtimer and previous work already computed
> diff --git a/drivers/gpu/drm/vkms/vkms_crtc.c b/drivers/gpu/drm/vkms/vkms_crtc.c
> index c727d8486e97..55b16d545fe7 100644
> --- a/drivers/gpu/drm/vkms/vkms_crtc.c
> +++ b/drivers/gpu/drm/vkms/vkms_crtc.c
> @@ -29,7 +29,7 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
>                 /* update frame_start only if a queued vkms_crc_work_handle()
>                  * has read the data
>                  */
> -               spin_lock(&output->state_lock);
> +               spin_lock(&output->crc_lock);
>                 if (!state->crc_pending)
>                         state->frame_start = frame;
>                 else
> @@ -37,7 +37,7 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
>                                          state->frame_start, frame);
>                 state->frame_end = frame;
>                 state->crc_pending = true;
> -               spin_unlock(&output->state_lock);
> +               spin_unlock(&output->crc_lock);
>
>                 ret = queue_work(output->crc_workq, &state->crc_work);
>                 if (!ret)
> @@ -224,7 +224,7 @@ 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);
> -       spin_lock_init(&vkms_out->state_lock);
> +       spin_lock_init(&vkms_out->crc_lock);
>
>         vkms_out->crc_workq = alloc_ordered_workqueue("vkms_crc_workq", 0);
>         if (!vkms_out->crc_workq)
> diff --git a/drivers/gpu/drm/vkms/vkms_drv.h b/drivers/gpu/drm/vkms/vkms_drv.h
> index 3c7e06b19efd..43d3f98289fe 100644
> --- a/drivers/gpu/drm/vkms/vkms_drv.h
> +++ b/drivers/gpu/drm/vkms/vkms_drv.h
> @@ -57,6 +57,7 @@ struct vkms_crtc_state {
>         struct drm_crtc_state base;
>         struct work_struct crc_work;
>
> +       /* below three are protected by vkms_output.crc_lock */
>         bool crc_pending;
>         u64 frame_start;
>         u64 frame_end;
> @@ -74,8 +75,8 @@ struct vkms_output {
>         struct workqueue_struct *crc_workq;
>         /* protects concurrent access to crc_data */
>         spinlock_t lock;

It's not really specific to this patch, but after reviewing it, I was
thinking about the use of the 'lock' field in the struct vkms_output.
Do we really need it? It looks like that crc_lock just replaced it.

Additionally, going a little bit deeper in the lock field at struct
vkms_output, I was also asking myself: what critical area do we want
to protect with this lock? After inspecting the use of this lock, I
noticed two different places that use it:

1. In the function vkms_vblank_simulate()

Note that we cover a vast area with ‘output->lock’. IMHO we just need
to protect the state variable (line “state = output->crc_state;”) and
we can also use crc_lock for this case. Make sense?

2. In the function vkms_crtc_atomic_begin()

We also hold output->lock in the vkms_crtc_atomic_begin() and just
release it at vkms_crtc_atomic_flush(). Do we still need it?

> -       /* protects concurrent access to crtc_state */
> -       spinlock_t state_lock;
> +
> +       spinlock_t crc_lock;
>  };

Maybe add a kernel doc on top of crc_lock?

>
>  struct vkms_device {
> --
> 2.20.1
>


-- 

Rodrigo Siqueira
https://siqueira.tech