diff mbox series

[v2,02/19] drm/i915/dsb: Use non-locked register access

Message ID 20230606191504.18099-3-ville.syrjala@linux.intel.com (mailing list archive)
State New, archived
Headers show
Series drm/i915: Load LUTs with DSB | expand

Commit Message

Ville Syrjälä June 6, 2023, 7:14 p.m. UTC 
From: Ville Syrjälä <ville.syrjala@linux.intel.com>

Avoid the locking overhead for DSB registers. We don't need the locks
and intel_dsb_commit() in particular needs to be called from the
vblank evade critical section and thus needs to be fast.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
---
 drivers/gpu/drm/i915/display/intel_dsb.c | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

Comments

Jani Nikula June 8, 2023, 11:46 a.m. UTC | #1 
On Tue, 06 Jun 2023, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>
> Avoid the locking overhead for DSB registers. We don't need the locks
> and intel_dsb_commit() in particular needs to be called from the
> vblank evade critical section and thus needs to be fast.

Mmmh, I always find it slightly puzzling to encounter _fw calls in code,
wondering what the rationale was, and why we can use the _fw variants.

Should we start adding comments explaining why?

BR,
Jani.


>
> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dsb.c | 18 +++++++++---------
>  1 file changed, 9 insertions(+), 9 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c b/drivers/gpu/drm/i915/display/intel_dsb.c
> index bed058d2c3ac..97e593d9f100 100644
> --- a/drivers/gpu/drm/i915/display/intel_dsb.c
> +++ b/drivers/gpu/drm/i915/display/intel_dsb.c
> @@ -96,7 +96,7 @@ static bool assert_dsb_has_room(struct intel_dsb *dsb)
>  static bool is_dsb_busy(struct drm_i915_private *i915, enum pipe pipe,
>  			enum dsb_id id)
>  {
> -	return intel_de_read(i915, DSB_CTRL(pipe, id)) & DSB_STATUS_BUSY;
> +	return intel_de_read_fw(i915, DSB_CTRL(pipe, id)) & DSB_STATUS_BUSY;
>  }
>  
>  static void intel_dsb_emit(struct intel_dsb *dsb, u32 ldw, u32 udw)
> @@ -243,13 +243,13 @@ void intel_dsb_commit(struct intel_dsb *dsb, bool wait_for_vblank)
>  		return;
>  	}
>  
> -	intel_de_write(dev_priv, DSB_CTRL(pipe, dsb->id),
> -		       (wait_for_vblank ? DSB_WAIT_FOR_VBLANK : 0) |
> -		       DSB_ENABLE);
> -	intel_de_write(dev_priv, DSB_HEAD(pipe, dsb->id),
> -		       i915_ggtt_offset(dsb->vma));
> -	intel_de_write(dev_priv, DSB_TAIL(pipe, dsb->id),
> -		       i915_ggtt_offset(dsb->vma) + tail);
> +	intel_de_write_fw(dev_priv, DSB_CTRL(pipe, dsb->id),
> +			  (wait_for_vblank ? DSB_WAIT_FOR_VBLANK : 0) |
> +			  DSB_ENABLE);
> +	intel_de_write_fw(dev_priv, DSB_HEAD(pipe, dsb->id),
> +			  i915_ggtt_offset(dsb->vma));
> +	intel_de_write_fw(dev_priv, DSB_TAIL(pipe, dsb->id),
> +			  i915_ggtt_offset(dsb->vma) + tail);
>  }
>  
>  void intel_dsb_wait(struct intel_dsb *dsb)
> @@ -266,7 +266,7 @@ void intel_dsb_wait(struct intel_dsb *dsb)
>  	/* Attempt to reset it */
>  	dsb->free_pos = 0;
>  	dsb->ins_start_offset = 0;
> -	intel_de_write(dev_priv, DSB_CTRL(pipe, dsb->id), 0);
> +	intel_de_write_fw(dev_priv, DSB_CTRL(pipe, dsb->id), 0);
>  }
>  
>  /**
Shankar, Uma Sept. 11, 2023, 8:22 p.m. UTC | #2 
> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf Of Jani
> Nikula
> Sent: Thursday, June 8, 2023 5:16 PM
> To: Ville Syrjala <ville.syrjala@linux.intel.com>; intel-gfx@lists.freedesktop.org
> Subject: Re: [Intel-gfx] [PATCH v2 02/19] drm/i915/dsb: Use non-locked register
> access
> 
> On Tue, 06 Jun 2023, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >
> > Avoid the locking overhead for DSB registers. We don't need the locks
> > and intel_dsb_commit() in particular needs to be called from the
> > vblank evade critical section and thus needs to be fast.
> 
> Mmmh, I always find it slightly puzzling to encounter _fw calls in code, wondering
> what the rationale was, and why we can use the _fw variants.
> 
> Should we start adding comments explaining why?

I believe it’s a light weight write without any locks and forcewake.
Maybe a comment to explain the rationale would be good.

With that added, this is:
Reviewed-by: Uma Shankar <uma.shankar@intel.com>

> BR,
> Jani.
> 
> 
> >
> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/display/intel_dsb.c | 18 +++++++++---------
> >  1 file changed, 9 insertions(+), 9 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c
> > b/drivers/gpu/drm/i915/display/intel_dsb.c
> > index bed058d2c3ac..97e593d9f100 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dsb.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dsb.c
> > @@ -96,7 +96,7 @@ static bool assert_dsb_has_room(struct intel_dsb
> > *dsb)  static bool is_dsb_busy(struct drm_i915_private *i915, enum pipe pipe,
> >  			enum dsb_id id)
> >  {
> > -	return intel_de_read(i915, DSB_CTRL(pipe, id)) & DSB_STATUS_BUSY;
> > +	return intel_de_read_fw(i915, DSB_CTRL(pipe, id)) & DSB_STATUS_BUSY;
> >  }
> >
> >  static void intel_dsb_emit(struct intel_dsb *dsb, u32 ldw, u32 udw)
> > @@ -243,13 +243,13 @@ void intel_dsb_commit(struct intel_dsb *dsb, bool
> wait_for_vblank)
> >  		return;
> >  	}
> >
> > -	intel_de_write(dev_priv, DSB_CTRL(pipe, dsb->id),
> > -		       (wait_for_vblank ? DSB_WAIT_FOR_VBLANK : 0) |
> > -		       DSB_ENABLE);
> > -	intel_de_write(dev_priv, DSB_HEAD(pipe, dsb->id),
> > -		       i915_ggtt_offset(dsb->vma));
> > -	intel_de_write(dev_priv, DSB_TAIL(pipe, dsb->id),
> > -		       i915_ggtt_offset(dsb->vma) + tail);
> > +	intel_de_write_fw(dev_priv, DSB_CTRL(pipe, dsb->id),
> > +			  (wait_for_vblank ? DSB_WAIT_FOR_VBLANK : 0) |
> > +			  DSB_ENABLE);
> > +	intel_de_write_fw(dev_priv, DSB_HEAD(pipe, dsb->id),
> > +			  i915_ggtt_offset(dsb->vma));
> > +	intel_de_write_fw(dev_priv, DSB_TAIL(pipe, dsb->id),
> > +			  i915_ggtt_offset(dsb->vma) + tail);
> >  }
> >
> >  void intel_dsb_wait(struct intel_dsb *dsb) @@ -266,7 +266,7 @@ void
> > intel_dsb_wait(struct intel_dsb *dsb)
> >  	/* Attempt to reset it */
> >  	dsb->free_pos = 0;
> >  	dsb->ins_start_offset = 0;
> > -	intel_de_write(dev_priv, DSB_CTRL(pipe, dsb->id), 0);
> > +	intel_de_write_fw(dev_priv, DSB_CTRL(pipe, dsb->id), 0);
> >  }
> >
> >  /**
> 
> --
> Jani Nikula, Intel Open Source Graphics Center
Jani Nikula Sept. 12, 2023, 7:37 a.m. UTC | #3 
On Mon, 11 Sep 2023, "Shankar, Uma" <uma.shankar@intel.com> wrote:
>> -----Original Message-----
>> From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf Of Jani
>> Nikula
>> Sent: Thursday, June 8, 2023 5:16 PM
>> To: Ville Syrjala <ville.syrjala@linux.intel.com>; intel-gfx@lists.freedesktop.org
>> Subject: Re: [Intel-gfx] [PATCH v2 02/19] drm/i915/dsb: Use non-locked register
>> access
>> 
>> On Tue, 06 Jun 2023, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
>> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> >
>> > Avoid the locking overhead for DSB registers. We don't need the locks
>> > and intel_dsb_commit() in particular needs to be called from the
>> > vblank evade critical section and thus needs to be fast.
>> 
>> Mmmh, I always find it slightly puzzling to encounter _fw calls in code, wondering
>> what the rationale was, and why we can use the _fw variants.
>> 
>> Should we start adding comments explaining why?
>
> I believe it’s a light weight write without any locks and forcewake.

That part is clear; the why isn't. :)

> Maybe a comment to explain the rationale would be good.
>
> With that added, this is:
> Reviewed-by: Uma Shankar <uma.shankar@intel.com>
>
>> BR,
>> Jani.
>> 
>> 
>> >
>> > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> > ---
>> >  drivers/gpu/drm/i915/display/intel_dsb.c | 18 +++++++++---------
>> >  1 file changed, 9 insertions(+), 9 deletions(-)
>> >
>> > diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c
>> > b/drivers/gpu/drm/i915/display/intel_dsb.c
>> > index bed058d2c3ac..97e593d9f100 100644
>> > --- a/drivers/gpu/drm/i915/display/intel_dsb.c
>> > +++ b/drivers/gpu/drm/i915/display/intel_dsb.c
>> > @@ -96,7 +96,7 @@ static bool assert_dsb_has_room(struct intel_dsb
>> > *dsb)  static bool is_dsb_busy(struct drm_i915_private *i915, enum pipe pipe,
>> >  			enum dsb_id id)
>> >  {
>> > -	return intel_de_read(i915, DSB_CTRL(pipe, id)) & DSB_STATUS_BUSY;
>> > +	return intel_de_read_fw(i915, DSB_CTRL(pipe, id)) & DSB_STATUS_BUSY;
>> >  }
>> >
>> >  static void intel_dsb_emit(struct intel_dsb *dsb, u32 ldw, u32 udw)
>> > @@ -243,13 +243,13 @@ void intel_dsb_commit(struct intel_dsb *dsb, bool
>> wait_for_vblank)
>> >  		return;
>> >  	}
>> >
>> > -	intel_de_write(dev_priv, DSB_CTRL(pipe, dsb->id),
>> > -		       (wait_for_vblank ? DSB_WAIT_FOR_VBLANK : 0) |
>> > -		       DSB_ENABLE);
>> > -	intel_de_write(dev_priv, DSB_HEAD(pipe, dsb->id),
>> > -		       i915_ggtt_offset(dsb->vma));
>> > -	intel_de_write(dev_priv, DSB_TAIL(pipe, dsb->id),
>> > -		       i915_ggtt_offset(dsb->vma) + tail);
>> > +	intel_de_write_fw(dev_priv, DSB_CTRL(pipe, dsb->id),
>> > +			  (wait_for_vblank ? DSB_WAIT_FOR_VBLANK : 0) |
>> > +			  DSB_ENABLE);
>> > +	intel_de_write_fw(dev_priv, DSB_HEAD(pipe, dsb->id),
>> > +			  i915_ggtt_offset(dsb->vma));
>> > +	intel_de_write_fw(dev_priv, DSB_TAIL(pipe, dsb->id),
>> > +			  i915_ggtt_offset(dsb->vma) + tail);
>> >  }
>> >
>> >  void intel_dsb_wait(struct intel_dsb *dsb) @@ -266,7 +266,7 @@ void
>> > intel_dsb_wait(struct intel_dsb *dsb)
>> >  	/* Attempt to reset it */
>> >  	dsb->free_pos = 0;
>> >  	dsb->ins_start_offset = 0;
>> > -	intel_de_write(dev_priv, DSB_CTRL(pipe, dsb->id), 0);
>> > +	intel_de_write_fw(dev_priv, DSB_CTRL(pipe, dsb->id), 0);
>> >  }
>> >
>> >  /**
>> 
>> --
>> Jani Nikula, Intel Open Source Graphics Center
Shankar, Uma Sept. 12, 2023, 7:49 a.m. UTC | #4 
> -----Original Message-----
> From: Jani Nikula <jani.nikula@linux.intel.com>
> Sent: Tuesday, September 12, 2023 1:08 PM
> To: Shankar, Uma <uma.shankar@intel.com>; Ville Syrjala
> <ville.syrjala@linux.intel.com>; intel-gfx@lists.freedesktop.org
> Subject: RE: [Intel-gfx] [PATCH v2 02/19] drm/i915/dsb: Use non-locked register
> access
> 
> On Mon, 11 Sep 2023, "Shankar, Uma" <uma.shankar@intel.com> wrote:
> >> -----Original Message-----
> >> From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf
> >> Of Jani Nikula
> >> Sent: Thursday, June 8, 2023 5:16 PM
> >> To: Ville Syrjala <ville.syrjala@linux.intel.com>;
> >> intel-gfx@lists.freedesktop.org
> >> Subject: Re: [Intel-gfx] [PATCH v2 02/19] drm/i915/dsb: Use
> >> non-locked register access
> >>
> >> On Tue, 06 Jun 2023, Ville Syrjala <ville.syrjala@linux.intel.com> wrote:
> >> > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >> >
> >> > Avoid the locking overhead for DSB registers. We don't need the
> >> > locks and intel_dsb_commit() in particular needs to be called from
> >> > the vblank evade critical section and thus needs to be fast.
> >>
> >> Mmmh, I always find it slightly puzzling to encounter _fw calls in
> >> code, wondering what the rationale was, and why we can use the _fw
> variants.
> >>
> >> Should we start adding comments explaining why?
> >
> > I believe it’s a light weight write without any locks and forcewake.
> 
> That part is clear; the why isn't. :)

Yes I agree, to add the reasoning will be good
diff mbox series

Patch

diff --git a/drivers/gpu/drm/i915/display/intel_dsb.c b/drivers/gpu/drm/i915/display/intel_dsb.c
index bed058d2c3ac..97e593d9f100 100644
--- a/drivers/gpu/drm/i915/display/intel_dsb.c
+++ b/drivers/gpu/drm/i915/display/intel_dsb.c
@@ -96,7 +96,7 @@  static bool assert_dsb_has_room(struct intel_dsb *dsb)
 static bool is_dsb_busy(struct drm_i915_private *i915, enum pipe pipe,
 			enum dsb_id id)
 {
-	return intel_de_read(i915, DSB_CTRL(pipe, id)) & DSB_STATUS_BUSY;
+	return intel_de_read_fw(i915, DSB_CTRL(pipe, id)) & DSB_STATUS_BUSY;
 }
 
 static void intel_dsb_emit(struct intel_dsb *dsb, u32 ldw, u32 udw)
@@ -243,13 +243,13 @@  void intel_dsb_commit(struct intel_dsb *dsb, bool wait_for_vblank)
 		return;
 	}
 
-	intel_de_write(dev_priv, DSB_CTRL(pipe, dsb->id),
-		       (wait_for_vblank ? DSB_WAIT_FOR_VBLANK : 0) |
-		       DSB_ENABLE);
-	intel_de_write(dev_priv, DSB_HEAD(pipe, dsb->id),
-		       i915_ggtt_offset(dsb->vma));
-	intel_de_write(dev_priv, DSB_TAIL(pipe, dsb->id),
-		       i915_ggtt_offset(dsb->vma) + tail);
+	intel_de_write_fw(dev_priv, DSB_CTRL(pipe, dsb->id),
+			  (wait_for_vblank ? DSB_WAIT_FOR_VBLANK : 0) |
+			  DSB_ENABLE);
+	intel_de_write_fw(dev_priv, DSB_HEAD(pipe, dsb->id),
+			  i915_ggtt_offset(dsb->vma));
+	intel_de_write_fw(dev_priv, DSB_TAIL(pipe, dsb->id),
+			  i915_ggtt_offset(dsb->vma) + tail);
 }
 
 void intel_dsb_wait(struct intel_dsb *dsb)
@@ -266,7 +266,7 @@  void intel_dsb_wait(struct intel_dsb *dsb)
 	/* Attempt to reset it */
 	dsb->free_pos = 0;
 	dsb->ins_start_offset = 0;
-	intel_de_write(dev_priv, DSB_CTRL(pipe, dsb->id), 0);
+	intel_de_write_fw(dev_priv, DSB_CTRL(pipe, dsb->id), 0);
 }
 
 /**