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

[Rodrigo Vivi <rodrigo.vivi@intel.com>]

On Tue, Mar 28, 2023 at 07:22:24PM +0300, Jani Nikula wrote:
> On Mon, 27 Mar 2023, Rodrigo Vivi <rodrigo.vivi@intel.com> 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>
> > Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Link: https://patchwork.freedesktop.org/patch/msgid/20230308165859.235520-1-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.
> > -	 */
> > -	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 0b5509f268a7..e4da8902c878 100644
> > --- a/drivers/gpu/drm/i915/display/intel_display_core.h
> > +++ b/drivers/gpu/drm/i915/display/intel_display_core.h
> > @@ -264,6 +264,9 @@ 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 12b5296ee744..e90a0c0403a6 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);
> 
> Can we do this in i9xx_wm_init() instead?

I was going to modify it here right now, but then I noticed
the cases above and remembered why I have put it here.
All the display locks are getting set in here.

Probably better to move with this patch as is and then add
a new on top moving the various locks to its individual inits?

> 
> 
> >  
> >  	i915_memcpy_init_early(dev_priv);
> >  	intel_runtime_pm_init_early(&dev_priv->runtime_pm);
> 
> -- 
> Jani Nikula, Intel Open Source Graphics Center