On Mon, Dec 05, 2022 at 12:50:40PM +0000, Tvrtko Ursulin wrote: > > On 02/12/2022 22:49, Rodrigo Vivi wrote: > > On Fri, Dec 02, 2022 at 02:35:28PM -0800, Matt Roper wrote: > > > When determining whether the platform has a hardware-level steering > > > semaphore (i.e., MTL and beyond), we need to use GRAPHICS_VER_FULL() to > > > compare the full version rather than just the major version number > > > returned by GRAPHICS_VER(). > > > > > > Reported-by: kernel test robot <l...@intel.com> > > > Fixes: 3100240bf846 ("drm/i915/mtl: Add hardware-level lock for steering") > > > Cc: Balasubramani Vivekanandan <balasubramani.vivekanan...@intel.com> > > > Signed-off-by: Matt Roper <matthew.d.ro...@intel.com> > > > > Reviewed-by: Rodrigo Vivi <rodrigo.v...@intel.com> > > > --- > > > drivers/gpu/drm/i915/gt/intel_gt_mcr.c | 4 ++-- > > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > > > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c > > > b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c > > > index 087e4ac5b68d..41a237509dcf 100644 > > > --- a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c > > > +++ b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c > > > @@ -367,7 +367,7 @@ void intel_gt_mcr_lock(struct intel_gt *gt, unsigned > > > long *flags) > > > * driver threads, but also with hardware/firmware agents. A > > > dedicated > > > * locking register is used. > > > */ > > > - if (GRAPHICS_VER(gt->i915) >= IP_VER(12, 70)) > > > + if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70)) > > Ouch, tricky class of bugs... Anyone has an idea how to maybe coerce the > compiler into spotting them for us, cheaply?
I believe clang can already notice these problems with Wtautological-constant-out-of-range-compare (which is how the kernel test robot finds them): >> drivers/gpu/drm/i915/gt/intel_gt_mcr.c:370:29: warning: result of comparison of constant 3142 with expression of type 'u8' (aka 'unsigned char') +is always false [-Wtautological-constant-out-of-range-compare] if (GRAPHICS_VER(gt->i915) >= IP_VER(12, 70)) ~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~ drivers/gpu/drm/i915/gt/intel_gt_mcr.c:410:29: warning: result of comparison of constant 3142 with expression of type 'u8' (aka 'unsigned char') +is always false [-Wtautological-constant-out-of-range-compare] if (GRAPHICS_VER(gt->i915) >= IP_VER(12, 70)) ~~~~~~~~~~~~~~~~~~~~~~ ^ ~~~~~~~~~~~~~~ 2 warnings generated. Unfortunately gcc doesn't seem to have anything equivalent as far as I can see. > > This one is undefined behaviour I think so not good: > > -#define IP_VER(ver, rel) ((ver) << 8 | (rel)) > +typedef void * i915_full_ver_t; > + > +#define IP_VER(ver, rel) (i915_full_ver_t)(unsigned long)((ver) << 8 | (rel)) Hmm, so by casting it into a pointer, you're hoping to trigger a "comparison of pointer and integer without cast" warning on misuse? That's a good idea, but as you noted, the C99 spec says comparison of pointers is only guaranteed to work if both are pointers into the same structure/array, otherwise the results are technically undefined. Matt > > Regards, > > Tvrtko > > > > err = wait_for(intel_uncore_read_fw(gt->uncore, > > > > > > MTL_STEER_SEMAPHORE) == 0x1, 100); > > > @@ -407,7 +407,7 @@ void intel_gt_mcr_unlock(struct intel_gt *gt, > > > unsigned long flags) > > > { > > > spin_unlock_irqrestore(>->mcr_lock, flags); > > > - if (GRAPHICS_VER(gt->i915) >= IP_VER(12, 70)) > > > + if (GRAPHICS_VER_FULL(gt->i915) >= IP_VER(12, 70)) > > > intel_uncore_write_fw(gt->uncore, MTL_STEER_SEMAPHORE, > > > 0x1); > > > } > > > -- > > > 2.38.1 > > > -- Matt Roper Graphics Software Engineer VTT-OSGC Platform Enablement Intel Corporation