Re: [PATCH] drm/i915: Extend residency counter ranges on chv and byt

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> On Thu, Mar 02, 2017 at 08:01:40PM +0200, Mika Kuoppala wrote:
>> We were passively acting on the high counter value bit
>> and as it was never set, we were only utilizing the
>> the 32bits of resolution. As the divisor with these platforms
>> is quite high, the wrap around happened in the less than 13 seconds.
>> 
>> If we toggle the resolution bit in the control register and
>> read twice we can get 8 bits more, bringing the wrap in
>> 54 minute range.
>> 
>> Reported-by: Len Brown <len.brown@intel.com>
> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=94852
>> Cc: Chris Wilson <chris@chris-wilson.co.uk>
>> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> Cc: Len Brown <len.brown@intel.com>
>> Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
>> ---
>>  drivers/gpu/drm/i915/i915_sysfs.c | 15 ++++++++++++---
>>  1 file changed, 12 insertions(+), 3 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/i915_sysfs.c b/drivers/gpu/drm/i915/i915_sysfs.c
>> index af0ac9f..807d7be 100644
>> --- a/drivers/gpu/drm/i915/i915_sysfs.c
>> +++ b/drivers/gpu/drm/i915/i915_sysfs.c
>> @@ -53,17 +53,26 @@ static u32 calc_residency(struct drm_i915_private *dev_priv,
>>  
>>  	/* On VLV and CHV, residency time is in CZ units rather than 1.28us */
>>  	if (IS_VALLEYVIEW(dev_priv) || IS_CHERRYVIEW(dev_priv)) {
>> -		units = 1;
>> +		u32 lower, upper;
>>  		div = dev_priv->czclk_freq;
>>  
>> -		if (I915_READ(VLV_COUNTER_CONTROL) & VLV_COUNT_RANGE_HIGH)
>> -			units <<= 8;
>> +		I915_WRITE(VLV_COUNTER_CONTROL,
>> +			   _MASKED_BIT_ENABLE(VLV_COUNT_RANGE_HIGH));
>> +		upper = I915_READ(reg);
>> +
>> +		I915_WRITE(VLV_COUNTER_CONTROL,
>> +			   _MASKED_BIT_DISABLE(VLV_COUNT_RANGE_HIGH));
>> +		lower = I915_READ(reg);
>
> Is this true??? There is an internal 40bit counter to which we have a
> 32bit window (i.e. changing the counter control doesn't reset the
> count).

Yes, evidence suggests so with prod byt. But I am not sure if same
holds true with chv.

>
> Note that you should recheck the high range afterwards to guard against
> constructing an erroneous value across wraparound. And this should also
> leave it set to high for other users on vlv.

Other user being debugs? Perhaps u64 utility function to read it
from both places then.

-Mika

> -Chris
>
> -- 
> Chris Wilson, Intel Open Source Technology Centre
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