Re: [PATCH] [v3] drm/i915: Clean up the ring scaling calculations

[Daniel Vetter <daniel@ffwll.ch>]

On Wed, Oct 02, 2013 at 09:36:04AM -0700, Jesse Barnes wrote:
> On Wed,  2 Oct 2013 09:25:02 -0700
> Ben Widawsky <benjamin.widawsky@intel.com> wrote:
> 
> > This patch attempts to clean up the ring/IA scaling programming in the
> > following ways.
> > 1. Fix the comment about the DDR frequency. The math is 266MHz, not
> > 133MHz. Formula was right, docs are wrong.
> > 
> > 2. Mask the DCLK register since I don't know how it is defined on future
> > platforms.
> > 
> > 3. use mult_frac instead of magic math.
> > 
> > This helps for future platform enabling.
> > 
> > v2: Actually use the right patch. The v1 was a mix of things, none of
> > which was right. Note that due to rounding, we actually get different
> > values (slightly higher) for the effective ring frequency.
> > 
> > v3: Use 1.25 instead of 1.33 as the original code did. (Jesse)
> > 
> > CC: Jesse Barnes <jbarnes@virtuousgeek.org>
> > CC: Chris Wilson <chris@chris-wilson.co.uk>
> > Signed-off-by: Ben Widawsky <ben@bwidawsk.net>
> > ---
> >  drivers/gpu/drm/i915/intel_pm.c | 8 ++++----
> >  1 file changed, 4 insertions(+), 4 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> > index 698257c..9753bd9 100644
> > --- a/drivers/gpu/drm/i915/intel_pm.c
> > +++ b/drivers/gpu/drm/i915/intel_pm.c
> > @@ -3663,9 +3663,9 @@ void gen6_update_ring_freq(struct drm_device *dev)
> >  	/* Convert from kHz to MHz */
> >  	max_ia_freq /= 1000;
> >  
> > -	min_ring_freq = I915_READ(MCHBAR_MIRROR_BASE_SNB + DCLK);
> > -	/* convert DDR frequency from units of 133.3MHz to bandwidth */
> > -	min_ring_freq = (2 * 4 * min_ring_freq + 2) / 3;
> > +	min_ring_freq = I915_READ(MCHBAR_MIRROR_BASE_SNB + DCLK) & 0xf;
> > +	/* convert DDR frequency from units of 266.6MHz to bandwidth */
> > +	min_ring_freq = mult_frac(min_ring_freq, 8, 3);
> >  
> >  	/*
> >  	 * For each potential GPU frequency, load a ring frequency we'd like
> > @@ -3678,7 +3678,7 @@ void gen6_update_ring_freq(struct drm_device *dev)
> >  		unsigned int ia_freq = 0, ring_freq = 0;
> >  
> >  		if (IS_HASWELL(dev)) {
> > -			ring_freq = (gpu_freq * 5 + 3) / 4;
> > +			ring_freq = mult_frac(gpu_freq, 5, 4);
> >  			ring_freq = max(min_ring_freq, ring_freq);
> >  			/* leave ia_freq as the default, chosen by cpufreq */
> >  		} else {
> 
> Reviewed-by: Jesse Barnes <jbarnes@virtuousgeek.org>

Queued for -next, thanks for the patch.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch