[Intel-gfx] [PATCH 7/8] drm/i915: Assert that our hpd pin bitmasks don't overflow

[Chris Wilson]

Quoting Ville Syrjälä (2018-07-05 18:51:16)
> On Thu, Jul 05, 2018 at 05:52:16PM +0100, Chris Wilson wrote:
> > Quoting Ville Syrjala (2018-07-05 17:43:56)
> > > From: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > 
> > > Make sure our hpd pin count doesn't exceed the bitmasks we use
> > > for tracking pending hotplugs. Not ever close to the limit yet,
> > > but no harm in making sure either.
> > > 
> > > Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > > ---
> > >  drivers/gpu/drm/i915/i915_irq.c | 2 ++
> > >  1 file changed, 2 insertions(+)
> > > 
> > > diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> > > index bb7c754979f8..c107e0837026 100644
> > > --- a/drivers/gpu/drm/i915/i915_irq.c
> > > +++ b/drivers/gpu/drm/i915/i915_irq.c
> > > @@ -1713,6 +1713,8 @@ static void intel_get_hpd_pins(struct drm_i915_private *dev_priv,
> > >  {
> > >         enum hpd_pin pin;
> > >  
> > > +       BUILD_BUG_ON(HPD_NUM_PINS > 32);
> > 
> > sizeof(*pin_mask) * CHAR_BIT ?
> 
> For a slightly more pleasing appearance I suppose we might want
> to steal BITS_PER_TYPE() from include/linux/net_dim.h. A quick 
> grep didn't seem to reveal anything similar in a more general
> location.

Yup, there's quite a few places that would be made more pleasant by
BITS_PER_TYPE().

> > Just looking for some explanation as where the limit comes from. Now
> > obviously u32, but why was u32 chosen?
> 
> Had the right kind of smell perhaps?

Ok, just curious if there was an intrinsic limit that could be captured
alongside the assert.
-Chris