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

[Chris Wilson]

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.
-Chris