Re: [Intel-gfx] [PATCH 1/2] drm/i915/display: Restore dsparb_lock.

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Mar 09, 2023 at 05:03:52PM -0500, Rodrigo Vivi wrote:
> On Thu, Mar 09, 2023 at 12:03:19AM +0200, Ville Syrjälä wrote:
> > On Wed, Mar 08, 2023 at 11:58:58AM -0500, Rodrigo Vivi wrote:
> > > uncore->lock only protects the forcewake domain itself,
> > > not the register accesses.
> > > 
> > > uncore's _fw alternatives are for cases where the domains
> > > are not needed because we are sure that they are already
> > > awake.
> > > 
> > > So the move towards the uncore's _fw alternatives seems
> > > right, however using the uncore-lock to protect the dsparb
> > > registers seems an abuse of the uncore-lock.
> > > 
> > > Let's restore the previous individual lock and try to get
> > > rid of the direct uncore accesses from the display code.
> > > 
> > > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > Cc: Jani Nikula <jani.nikula@intel.com>
> > > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/display/i9xx_wm.c            | 13 ++-----------
> > >  drivers/gpu/drm/i915/display/intel_display_core.h |  3 +++
> > >  drivers/gpu/drm/i915/i915_driver.c                |  1 +
> > >  3 files changed, 6 insertions(+), 11 deletions(-)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/display/i9xx_wm.c b/drivers/gpu/drm/i915/display/i9xx_wm.c
> > > index caef72d38798..8fe0b5c63d3a 100644
> > > --- a/drivers/gpu/drm/i915/display/i9xx_wm.c
> > > +++ b/drivers/gpu/drm/i915/display/i9xx_wm.c
> > > @@ -1771,16 +1771,7 @@ static void vlv_atomic_update_fifo(struct intel_atomic_state *state,
> > >  
> > >  	trace_vlv_fifo_size(crtc, sprite0_start, sprite1_start, fifo_size);
> > >  
> > > -	/*
> > > -	 * uncore.lock serves a double purpose here. It allows us to
> > > -	 * use the less expensive I915_{READ,WRITE}_FW() functions, and
> > > -	 * it protects the DSPARB registers from getting clobbered by
> > > -	 * parallel updates from multiple pipes.
> > > -	 *
> > > -	 * intel_pipe_update_start() has already disabled interrupts
> > > -	 * for us, so a plain spin_lock() is sufficient here.
> > > -	 */
> > 
> > I was wondering if we need to preserve the comment about irqs,
> > but since this is the only place using this lock, and it's never
> > called from an irq handler a non-irq disabling spinlock will suffice
> > anyway.
> > 
> > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> 
> thoughts on this: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_114868v2/fi-kbl-7567u/igt@kms_pipe_crc_basic@nonblocking-crc-frame-sequence@pipe-b-dp-1.html

This code doesn't run on that platform, so unrelated.

> 
> maybe related to the usage of this uncore.lock in
> 
> drivers/gpu/drm/i915/display/intel_vblank.c
> 
> ?
> 
> Should we create another spin lock and include both of these cases?
> (Then the irq comment is relevant again :))

We're already 4 spinlocks deep when in vblank code. Let's not add more ;)

> 
> > 
> > > -	spin_lock(&uncore->lock);
> > > +	spin_lock(&dev_priv->display.wm.dsparb_lock);
> > >  
> > >  	switch (crtc->pipe) {
> > >  	case PIPE_A:
> > > @@ -1840,7 +1831,7 @@ static void vlv_atomic_update_fifo(struct intel_atomic_state *state,
> > >  
> > >  	intel_uncore_posting_read_fw(uncore, DSPARB);
> > >  
> > > -	spin_unlock(&uncore->lock);
> > > +	spin_unlock(&dev_priv->display.wm.dsparb_lock);
> > >  }
> > >  
> > >  #undef VLV_FIFO
> > > diff --git a/drivers/gpu/drm/i915/display/intel_display_core.h b/drivers/gpu/drm/i915/display/intel_display_core.h
> > > index fdab7bb93a7d..68c6bfb91dbe 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_display_core.h
> > > +++ b/drivers/gpu/drm/i915/display/intel_display_core.h
> > > @@ -253,6 +253,9 @@ struct intel_wm {
> > >  	 */
> > >  	struct mutex wm_mutex;
> > >  
> > > +	/* protects DSPARB registers on pre-g4x/vlv/chv */
> > > +	spinlock_t dsparb_lock;
> > > +
> > >  	bool ipc_enabled;
> > >  };
> > >  
> > > diff --git a/drivers/gpu/drm/i915/i915_driver.c b/drivers/gpu/drm/i915/i915_driver.c
> > > index a53fd339e2cc..c78e36444a12 100644
> > > --- a/drivers/gpu/drm/i915/i915_driver.c
> > > +++ b/drivers/gpu/drm/i915/i915_driver.c
> > > @@ -223,6 +223,7 @@ static int i915_driver_early_probe(struct drm_i915_private *dev_priv)
> > >  	mutex_init(&dev_priv->display.pps.mutex);
> > >  	mutex_init(&dev_priv->display.hdcp.comp_mutex);
> > >  	spin_lock_init(&dev_priv->display.dkl.phy_lock);
> > > +	spin_lock_init(&dev_priv->display.wm.dsparb_lock);
> > >  
> > >  	i915_memcpy_init_early(dev_priv);
> > >  	intel_runtime_pm_init_early(&dev_priv->runtime_pm);
> > > -- 
> > > 2.39.2
> > 
> > -- 
> > Ville Syrjälä
> > Intel

-- 
Ville Syrjälä
Intel