drm/i915: Use the real cpu max frequency for ring scaling

The policy's max frequency is not equal to the CPU's max frequency. The
ring frequency is derived from the CPU frequency, and not the policy
frequency.

One example of how this may differ through sysfs. If the sysfs max
frequency is modified, that will be used for the max ring frequency
calculation.
(/sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq). As far as I
know, no current governor uses anything but max as the default, but in
theory, they could. Similarly distributions might set policy as part of
their init process.

It's ideal to use the real frequency because when we're currently scaled
up on the GPU. In this case we likely want to race to idle, and using a
less than max ring frequency is non-optimal for this situation.

AFAIK, this patch should have no impact on a majority of people.

This behavior hasn't been changed since it was first introduced:
commit 23b2f8bb92feb83127679c53633def32d3108e70
Author: Jesse Barnes <[email protected]>
Date:   Tue Jun 28 13:04:16 2011 -0700

    drm/i915: load a ring frequency scaling table v3

CC: Jesse Barnes <[email protected]>
Signed-off-by: Ben Widawsky <[email protected]>
Reviewed-by: Chris Wilson <[email protected]>
Signed-off-by: Rodrigo Vivi <[email protected]>
Signed-off-by: Daniel Vetter <[email protected]>

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index da24825acc84a3c6d0256f62bc314d3eb7285fcf..9534e72fdbcbb8c0ca83d77758b424cb7482e618 100644 (file)
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -3740,16 +3740,21 @@ void gen6_update_ring_freq(struct drm_device *dev)
        unsigned int gpu_freq;
        unsigned int max_ia_freq, min_ring_freq;
        int scaling_factor = 180;
+       struct cpufreq_policy *policy;
 
        WARN_ON(!mutex_is_locked(&dev_priv->rps.hw_lock));
 
-       max_ia_freq = cpufreq_quick_get_max(0);
-       /*
-        * Default to measured freq if none found, PCU will ensure we don't go
-        * over
-        */
-       if (!max_ia_freq)
+       policy = cpufreq_cpu_get(0);
+       if (policy) {
+               max_ia_freq = policy->cpuinfo.max_freq;
+               cpufreq_cpu_put(policy);
+       } else {
+               /*
+                * Default to measured freq if none found, PCU will ensure we
+                * don't go over
+                */
                max_ia_freq = tsc_khz;
+       }
 
        /* Convert from kHz to MHz */
        max_ia_freq /= 1000;