[Intel-gfx] [PATCH v3] drm/i915: Speed up DMC firmware loading

[Chris Wilson]

Quoting Chris Wilson (2017-09-04 20:14:32)
> Quoting David Weinehall (2017-09-04 20:08:06)
> > Currently we're doing:
> > 
> > 1. acquire lock
> > 2. write word to hardware
> > 3. release lock
> > 4. repeat from 1
> > 
> > to load the DMC firmware. Due to the cost of acquiring/releasing a lock,
> > and the size of the DMC firmware, this slows down DMC loading a lot.
> > 
> > This patch simply acquires the lock, writes the entire firmware,
> > then releases the lock.  Testing shows resume speedups
> > in the order of 10ms on platforms with DMC firmware (GEN9+).
> > 
> > v2: Per feedback from Chris & Ville there's no need to do the whole
> >     forcewake dance, so lose that bit (Chris, Ville)
> > 
> > v3: Actually send the new version of the patch...
> > 
> > Signed-off-by: David Weinehall <david.weinehall at linux.intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_csr.c | 8 +++++++-
> >  1 file changed, 7 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_csr.c b/drivers/gpu/drm/i915/intel_csr.c
> > index 965988f79a55..28ea24932ef1 100644
> > --- a/drivers/gpu/drm/i915/intel_csr.c
> > +++ b/drivers/gpu/drm/i915/intel_csr.c
> > @@ -240,6 +240,7 @@ void intel_csr_load_program(struct drm_i915_private *dev_priv)
> >  {
> >         u32 *payload = dev_priv->csr.dmc_payload;
> >         uint32_t i, fw_size;
> > +       unsigned long flags;
> >  
> >         if (!HAS_CSR(dev_priv)) {
> >                 DRM_ERROR("No CSR support available for this platform\n");
> > @@ -252,8 +253,13 @@ void intel_csr_load_program(struct drm_i915_private *dev_priv)
> >         }
> >  
> >         fw_size = dev_priv->csr.dmc_fw_size;
> > +       assert_rpm_wakelock_held(dev_priv);
> > +       spin_lock_irqsave(&dev_priv->uncore.lock, flags);
> > +
> >         for (i = 0; i < fw_size; i++)
> > -               I915_WRITE(CSR_PROGRAM(i), payload[i]);
> > +               I915_WRITE_FW(CSR_PROGRAM(i), payload[i]);
> > +
> > +       spin_unlock_irqrestore(&dev_priv->uncore.lock, flags);
> 
> Still would like to see the version without the uncore.lock. Afaict,
> there isn't a requirement here -- unless you are serialising between
> multiple users (concurrent intel_csr_load_program?) of CSR_PROGRAM.

You may also want to consider a preempt_disable around this block as
well, the argument being that we want the writes tightly grouped.
-Chris