[Intel-gfx] i915: WARN_ON(val > dev_priv->rps.max_freq_softlimit)

[Ville Syrjälä]

On Wed, Jan 28, 2015 at 09:58:15AM +0000, Chris Wilson wrote:
> On Wed, Jan 28, 2015 at 12:43:21AM -0500, Michael Auchter wrote:
> > Testing out 3.19-rc6 on my 2014 Thinkpad X1 Carbon (Haswell) resulted in
> > this WARN at boot (and pretty frequently afterwards):
> > 
> > WARNING: CPU: 0 PID: 989 at drivers/gpu/drm/i915/intel_pm.c:4377 gen6_set_rps+0x371/0x3c0()
> > WARN_ON(val > dev_priv->rps.max_freq_softlimit)
> 
> [snip]
>  
> > I'm not at all familiar with this hardware, but I took a quick look into
> > what changed with this commit for my laptop. Before the commit,
> > rps.min_freq_softlimit is 4 (from rps.min_freq) and
> > rps.max_freq_softlimit is 22.
> > 
> > After the commit, rps.min_freq_softlimit is set to the
> > rps.efficient_freq value read from pcode, which is 34 on my laptop.
> > So later when gen6_set_rps() is called with rps.min_freq_softlimit that
> > warning is hit.
> > 
> > Any thoughts? It certainly seems fishy that this commit causes
> > rps.min_freq_softlimit to be greater than rps.max_freq_softlimit.
> 
> Very fishy indeed. Moral of this story, never trust hw.
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 3e630feb18e4..bbedd2901c54 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4007,7 +4007,10 @@ static void gen6_init_rps_frequencies(struct drm_device *dev)
>                                         &ddcc_status);
>                 if (0 == ret)
>                         dev_priv->rps.efficient_freq =
> -                               (ddcc_status >> 8) & 0xff;
> +                               clamp_t(u8,
> +                                       (ddcc_status >> 8) & 0xff,
> +                                       dev_priv->rps.min_freq,
> +                                       dev_priv->rps.max_freq);

Maybe better to fall back to rp1_freq if this is bogus?

>         }
>  
>         /* Preserve min/max settings in case of re-init */
> 
> But really it is probably just best to disable the query for hsw:
> 
> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
> index 3e630feb18e4..01bd508e81f6 100644
> --- a/drivers/gpu/drm/i915/intel_pm.c
> +++ b/drivers/gpu/drm/i915/intel_pm.c
> @@ -4001,7 +4001,7 @@ static void gen6_init_rps_frequencies(struct drm_device *dev)
>         dev_priv->rps.max_freq          = dev_priv->rps.rp0_freq;
>  
>         dev_priv->rps.efficient_freq = dev_priv->rps.rp1_freq;
> -       if (IS_HASWELL(dev) || IS_BROADWELL(dev)) {
> +       if (IS_BROADWELL(dev)) {
>                 ret = sandybridge_pcode_read(dev_priv,
>                                         HSW_PCODE_DYNAMIC_DUTY_CYCLE_CONTROL,
>                                         &ddcc_status);
> 
> Paranoia says we do both.
> -Chris
> 
> -- 
> Chris Wilson, Intel Open Source Technology Centre
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> Intel-gfx at lists.freedesktop.org
> http://lists.freedesktop.org/mailman/listinfo/intel-gfx

-- 
Ville Syrjälä
Intel OTC