Re: [PATCH 3/3] drm/i915: Use vblank evade mechanism in mmio_flip

[Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>]

Hi Paulo,

Thanks for reviewing.

On 11/03/2014 08:37 PM, Paulo Zanoni wrote:
> 2014-10-28 11:10 GMT-02:00 Ander Conselvan de Oliveira
> <ander.conselvan.de.oliveira@intel.com>:
>> Currently we program just DPSCNTR and DSPSTRIDE directly from the ring
>> interrupt handler, which is fine since the hardware guarantees that
>> those are update atomically. When we have atomic page flips we'll want
>> to be able to update also the offset registers, and then we need to use
>> the vblank evade mechanism to guarantee atomicity. Since that mechanism
>> introduces a wait, we need to do the actual register write from a work
>> when it is triggered by the ring interrupt.
>>
>> v2: Explain the need for mmio_flip.work in the commit message (Paulo)
>>      Initialize the mmio_flip work in intel_crtc_init() (Paulo)
>>      Prevent new flips the previous flip work finishes (Paulo)
>>      Don't acquire modeset locks for mmio flip work
>>
>> Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
>> ---
>>   drivers/gpu/drm/i915/intel_display.c | 30 ++++++++++++++++++++++++++----
>>   drivers/gpu/drm/i915/intel_drv.h     | 12 +++++++++++-
>>   drivers/gpu/drm/i915/intel_sprite.c  |  4 ++--
>>   3 files changed, 39 insertions(+), 7 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
>> index 8965f2d..86c2051 100644
>> --- a/drivers/gpu/drm/i915/intel_display.c
>> +++ b/drivers/gpu/drm/i915/intel_display.c
>> @@ -9314,11 +9314,15 @@ static void intel_do_mmio_flip(struct intel_crtc *intel_crtc)
>>          struct intel_framebuffer *intel_fb =
>>                  to_intel_framebuffer(intel_crtc->base.primary->fb);
>>          struct drm_i915_gem_object *obj = intel_fb->obj;
>> +       bool atomic_update;
>> +       u32 start_vbl_count;
>>          u32 dspcntr;
>>          u32 reg;
>>
>>          intel_mark_page_flip_active(intel_crtc);
>>
>> +       atomic_update = intel_pipe_update_start(intel_crtc, &start_vbl_count);
>
> Don't we want to print something (error message?) in case this returns false?

Good question. The function itself has a warn for one of the failure 
cases (when drm_vblank_get() fails) but it doesn't print anything if the 
calculation for min and max scanlines fails. It seems the latter case 
would fail if we have a bad mode (with vblank_start <= 1) or in some 
unrealistic scenarios involving a combination of low pixel clocks and 
high htotal.

In any case, I guess we would be better to add a the warning to 
intel_pipe_update_start() itself, since there are other users that 
follow the same pattern.

Ander


> Besides this, my only worry is what is going to happen if we disable
> the CRTC or plane (or even suspend - S3 or runtime - or something like
> that) after we schedule the work, but before the work actually
> happens. Isn't it possible to end up accidentally reenabling something
> that was just disabled? We can't seem to queue a new flip before the
> current one finishes, but maybe we can shut down the CRTC while the
> work is scheduled? I don't know much about vblanks to properly answer
> that, so I'll let Daniel/Ville take a look at this.
>
> Everything else looks correct, so if someone guarantees the above
> question is not a problem: Reviewed-by: Paulo Zanoni
> <paulo.r.zanoni@intel.com>
>
>> +
>>          reg = DSPCNTR(intel_crtc->plane);
>>          dspcntr = I915_READ(reg);
>>
>> @@ -9332,6 +9336,21 @@ static void intel_do_mmio_flip(struct intel_crtc *intel_crtc)
>>          I915_WRITE(DSPSURF(intel_crtc->plane),
>>                     intel_crtc->unpin_work->gtt_offset);
>>          POSTING_READ(DSPSURF(intel_crtc->plane));
>> +
>> +       if (atomic_update)
>> +               intel_pipe_update_end(intel_crtc, start_vbl_count);
>> +
>> +       spin_lock_irq(&dev_priv->mmio_flip_lock);
>> +       intel_crtc->mmio_flip.status = INTEL_MMIO_FLIP_IDLE;
>> +       spin_unlock_irq(&dev_priv->mmio_flip_lock);
>> +}
>> +
>> +static void intel_mmio_flip_work_func(struct work_struct *work)
>> +{
>> +       struct intel_crtc *intel_crtc =
>> +               container_of(work, struct intel_crtc, mmio_flip.work);
>> +
>> +       intel_do_mmio_flip(intel_crtc);
>>   }
>>
>>   static int intel_postpone_flip(struct drm_i915_gem_object *obj)
>> @@ -9374,15 +9393,15 @@ void intel_notify_mmio_flip(struct intel_engine_cs *ring)
>>                  struct intel_mmio_flip *mmio_flip;
>>
>>                  mmio_flip = &intel_crtc->mmio_flip;
>> -               if (mmio_flip->seqno == 0)
>> +               if (mmio_flip->status != INTEL_MMIO_FLIP_WAIT_RING)
>>                          continue;
>>
>>                  if (ring->id != mmio_flip->ring_id)
>>                          continue;
>>
>>                  if (i915_seqno_passed(seqno, mmio_flip->seqno)) {
>> -                       intel_do_mmio_flip(intel_crtc);
>> -                       mmio_flip->seqno = 0;
>> +                       schedule_work(&intel_crtc->mmio_flip.work);
>> +                       mmio_flip->status = INTEL_MMIO_FLIP_WORK_SCHEDULED;
>>                          ring->irq_put(ring);
>>                  }
>>          }
>> @@ -9400,7 +9419,7 @@ static int intel_queue_mmio_flip(struct drm_device *dev,
>>          struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
>>          int ret;
>>
>> -       if (WARN_ON(intel_crtc->mmio_flip.seqno))
>> +       if (WARN_ON(intel_crtc->mmio_flip.status != INTEL_MMIO_FLIP_IDLE))
>>                  return -EBUSY;
>>
>>          ret = intel_postpone_flip(obj);
>> @@ -9412,6 +9431,7 @@ static int intel_queue_mmio_flip(struct drm_device *dev,
>>          }
>>
>>          spin_lock_irq(&dev_priv->mmio_flip_lock);
>> +       intel_crtc->mmio_flip.status = INTEL_MMIO_FLIP_WAIT_RING;
>>          intel_crtc->mmio_flip.seqno = obj->last_write_seqno;
>>          intel_crtc->mmio_flip.ring_id = obj->ring->id;
>>          spin_unlock_irq(&dev_priv->mmio_flip_lock);
>> @@ -11883,6 +11903,8 @@ static void intel_crtc_init(struct drm_device *dev, int pipe)
>>          dev_priv->plane_to_crtc_mapping[intel_crtc->plane] = &intel_crtc->base;
>>          dev_priv->pipe_to_crtc_mapping[intel_crtc->pipe] = &intel_crtc->base;
>>
>> +       INIT_WORK(&intel_crtc->mmio_flip.work, intel_mmio_flip_work_func);
>> +
>>          drm_crtc_helper_add(&intel_crtc->base, &intel_helper_funcs);
>>
>>          WARN_ON(drm_crtc_index(&intel_crtc->base) != intel_crtc->pipe);
>> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
>> index d53ac23..ff4af6b 100644
>> --- a/drivers/gpu/drm/i915/intel_drv.h
>> +++ b/drivers/gpu/drm/i915/intel_drv.h
>> @@ -399,9 +399,17 @@ struct intel_pipe_wm {
>>          bool sprites_scaled;
>>   };
>>
>> +enum intel_mmio_flip_status {
>> +       INTEL_MMIO_FLIP_IDLE = 0,
>> +       INTEL_MMIO_FLIP_WAIT_RING,
>> +       INTEL_MMIO_FLIP_WORK_SCHEDULED,
>> +};
>> +
>>   struct intel_mmio_flip {
>>          u32 seqno;
>>          u32 ring_id;
>> +       enum intel_mmio_flip_status status;
>> +       struct work_struct work;
>>   };
>>
>>   struct intel_crtc {
>> @@ -1168,7 +1176,9 @@ int intel_sprite_set_colorkey(struct drm_device *dev, void *data,
>>                                struct drm_file *file_priv);
>>   int intel_sprite_get_colorkey(struct drm_device *dev, void *data,
>>                                struct drm_file *file_priv);
>> -
>> +bool intel_pipe_update_start(struct intel_crtc *crtc,
>> +                            uint32_t *start_vbl_count);
>> +void intel_pipe_update_end(struct intel_crtc *crtc, u32 start_vbl_count);
>>
>>   /* intel_tv.c */
>>   void intel_tv_init(struct drm_device *dev);
>> diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
>> index c1d9547..9e2a5e2 100644
>> --- a/drivers/gpu/drm/i915/intel_sprite.c
>> +++ b/drivers/gpu/drm/i915/intel_sprite.c
>> @@ -62,7 +62,7 @@ static int usecs_to_scanlines(const struct drm_display_mode *mode, int usecs)
>>    *
>>    * Return: true if the call was successful
>>    */
>> -static bool intel_pipe_update_start(struct intel_crtc *crtc, uint32_t *start_vbl_count)
>> +bool intel_pipe_update_start(struct intel_crtc *crtc, uint32_t *start_vbl_count)
>>   {
>>          struct drm_device *dev = crtc->base.dev;
>>          const struct drm_display_mode *mode = &crtc->config.adjusted_mode;
>> @@ -135,7 +135,7 @@ static bool intel_pipe_update_start(struct intel_crtc *crtc, uint32_t *start_vbl
>>    * re-enables interrupts and verifies the update was actually completed
>>    * before a vblank using the value of @start_vbl_count.
>>    */
>> -static void intel_pipe_update_end(struct intel_crtc *crtc, u32 start_vbl_count)
>> +void intel_pipe_update_end(struct intel_crtc *crtc, u32 start_vbl_count)
>>   {
>>          struct drm_device *dev = crtc->base.dev;
>>          enum pipe pipe = crtc->pipe;
>> --
>> 1.9.1
>>
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>> Intel-gfx@lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
>
>

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