On Fri, Feb 24, 2017 at 06:03:09PM -0300, Paulo Zanoni wrote:
> Em Qua, 2017-02-08 às 15:12 +0200, Joonas Lahtinen escreveu:
> > "BIT(max) - 1" will overflow when max = 32, and GCC will complain.
> > We already have GENMASK for generating the mask, use it!
> >
> > v2: Majestic off by one spotted (Chris)
> >
> > Signed-off-by: Joonas Lahtinen <joonas.lahtinen@xxxxxxxxxxxxxxx>
> > Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
> > ---
> > drivers/gpu/drm/i915/intel_device_info.c | 2 +-
> > drivers/gpu/drm/i915/intel_fbdev.c | 2 +-
> > drivers/gpu/drm/i915/intel_runtime_pm.c | 2 +-
> > 3 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_device_info.c
> > b/drivers/gpu/drm/i915/intel_device_info.c
> > index fcf8181..0891cc0 100644
> > --- a/drivers/gpu/drm/i915/intel_device_info.c
> > +++ b/drivers/gpu/drm/i915/intel_device_info.c
> > @@ -234,7 +234,7 @@ static void broadwell_sseu_info_init(struct
> > drm_i915_private *dev_priv)
> > * The subslice disable field is global, i.e. it applies
> > * to each of the enabled slices.
> > */
> > - sseu->subslice_mask = BIT(ss_max) - 1;
> > + sseu->subslice_mask = GENMASK(ss_max - 1, 0);
> > sseu->subslice_mask &= ~((fuse2 & GEN8_F2_SS_DIS_MASK) >>
> > GEN8_F2_SS_DIS_SHIFT);
> >
> > diff --git a/drivers/gpu/drm/i915/intel_fbdev.c
> > b/drivers/gpu/drm/i915/intel_fbdev.c
> > index 281c5c4..e6f3eb2d 100644
> > --- a/drivers/gpu/drm/i915/intel_fbdev.c
> > +++ b/drivers/gpu/drm/i915/intel_fbdev.c
> > @@ -369,7 +369,7 @@ static bool intel_fb_initial_config(struct
> > drm_fb_helper *fb_helper,
> > return false;
> >
> > memcpy(save_enabled, enabled, count);
> > - mask = BIT(count) - 1;
> > + mask = GENMASK(count - 1, 0);
>
> Due to some debugging accident I ended up with a machine where count is
> zero.
>
> In this case:
>
> "BIT(count) - 1" is 0
> "GENMASK(count - 1, 0)" is 0xFFFFFFFFFFFFFFFF
>
> The consequence is that the machine freezes after i915.ko is loaded.
>
> So we have a "short blanket" problem here: one solution is wrong for
> the maximum value while the other solution is wrong for the minimum
> value. Either your chest or your feet gets warm, not both.
>
> I see that "count" comes from fb_helper->connector_count. The
> drm_fb_helper.h documentation says that this is "number of connected
> connectors". So now I'm wondering that maybe zero is actually a
> possible value (outside of my accident), in which case this patch would
> be considered a regression. Maybe for those PCH_NONE/PCH_NOP cases?
>
> Perhaps we could only revert this specific chunk and keep the power
> domain chunk using GENMASK? Any other solutions?
>
> Also, I have no idea if the subslice_mask case would accept zero as
> input. I'll let you do the analysis of this piece of the code.
It's already been fixed (hopefully).
commit 754a76591b12c88f57ad8b4ca533a5c9566a1922
Author: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Date: Fri Feb 24 11:43:06 2017 +0000
drm/i915/fbdev: Stop repeating tile configuration on stagnation
-Chris
--
Chris Wilson, Intel Open Source Technology Centre
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