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From: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
To: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Daniel Vetter <daniel.vetter@intel.com>,
	DRI Development <dri-devel@lists.freedesktop.org>,
	Haneen Mohammed <hamohammed.sa@gmail.com>
Subject: Re: [PATCH 03/10] drm/vkms: Rename vkms_output.state_lock to crc_lock
Date: Wed, 12 Jun 2019 10:38:23 -0300	[thread overview]
Message-ID: <CADKXj+5oBpMqu_SDvRB=j7Brav2_MXDccqAkN4UHr3Piwn66pQ@mail.gmail.com> (raw)
In-Reply-To: <20190606222751.32567-4-daniel.vetter@ffwll.ch>

On Thu, Jun 6, 2019 at 7:28 PM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>
> Plus add a comment about what it actually protects. It's very little.
>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
> Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
> Cc: Daniel Vetter <daniel@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
_______________________________________________
dri-devel mailing list
dri-devel@lists.freedesktop.org
https://lists.freedesktop.org/mailman/listinfo/dri-devel

  reply	other threads:[~2019-06-12 13:38 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-06 22:27 [PATCH 00/10] drm/vkms: rework crc worker Daniel Vetter
2019-06-06 22:27 ` [PATCH 01/10] drm/vkms: Fix crc worker races Daniel Vetter
2019-06-12 13:33   ` Rodrigo Siqueira
2019-06-12 14:48     ` Daniel Vetter
2019-06-18  2:39       ` Rodrigo Siqueira
2019-06-18  8:49         ` Daniel Vetter
2019-06-06 22:27 ` [PATCH 02/10] drm/vkms: Use spin_lock_irq in process context Daniel Vetter
2019-06-12 13:34   ` Rodrigo Siqueira
2019-06-12 14:54     ` Daniel Vetter
2019-06-06 22:27 ` [PATCH 03/10] drm/vkms: Rename vkms_output.state_lock to crc_lock Daniel Vetter
2019-06-12 13:38   ` Rodrigo Siqueira [this message]
2019-06-13  7:48     ` Daniel Vetter
2019-06-06 22:27 ` [PATCH 04/10] drm/vkms: Move format arrays to vkms_plane.c Daniel Vetter
2019-06-12 13:39   ` Rodrigo Siqueira
2019-06-19  2:12   ` Rodrigo Siqueira
2019-06-06 22:27 ` [PATCH 05/10] drm/vkms: Add our own commit_tail Daniel Vetter
2019-06-06 22:27 ` [PATCH 06/10] drm/vkms: flush crc workers earlier in commit flow Daniel Vetter
2019-06-12 13:42   ` Rodrigo Siqueira
2019-06-13  7:53     ` Daniel Vetter
2019-06-13  7:55       ` Daniel Vetter
2019-06-18  2:31       ` Rodrigo Siqueira
2019-06-06 22:27 ` [PATCH 07/10] drm/vkms: Dont flush crc worker when we change crc status Daniel Vetter
2019-06-19  2:17   ` Rodrigo Siqueira
2019-06-19  7:47     ` Daniel Vetter
2019-06-06 22:27 ` [PATCH 08/10] drm/vkms: No _irqsave within spin_lock_irq needed Daniel Vetter
2019-06-12 13:43   ` Rodrigo Siqueira
2019-06-06 22:27 ` [PATCH 09/10] drm/vkms: totally reworked crc data tracking Daniel Vetter
2019-06-12 13:46   ` Rodrigo Siqueira
2019-06-13  7:59     ` Daniel Vetter
2019-06-06 22:27 ` [PATCH 10/10] drm/vkms: No need for ->pages_lock in crc work anymore Daniel Vetter
2019-06-12 13:47   ` Rodrigo Siqueira
2019-06-12 13:28 ` [PATCH 00/10] drm/vkms: rework crc worker Rodrigo Siqueira
2019-06-12 14:42   ` Daniel Vetter
2019-06-18  2:49     ` Rodrigo Siqueira
2019-06-18  8:56       ` Daniel Vetter
2019-06-18 21:54         ` Rodrigo Siqueira
2019-06-18 22:06           ` Daniel Vetter
2019-06-18 22:07             ` Daniel Vetter
2019-06-18 22:25               ` Rodrigo Siqueira
2019-06-18 22:39                 ` Daniel Vetter
2019-06-26  1:44             ` Rodrigo Siqueira
2019-06-26  7:54               ` Daniel Vetter
2019-06-26 13:46                 ` Rodrigo Siqueira
2019-07-01  3:30                 ` Rodrigo Siqueira

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