On 05/12/2022 16:27, Matt Roper wrote:
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 <lkp@xxxxxxxxx>
Fixes: 3100240bf846 ("drm/i915/mtl: Add hardware-level lock for steering")
Cc: Balasubramani Vivekanandan <balasubramani.vivekanandan@xxxxxxxxx>
Signed-off-by: Matt Roper <matthew.d.roper@xxxxxxxxx>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
---
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.
Hah.. curios how IS_ENABLED then works on clang builds. Maybe it has
some special handling for that flavour of "always false".
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.
"error: comparison between pointer and integer" - it works, but yes it
is undefined. Only == and != are allowed on random void * pointers.
Since you say clang builds report the problem we are good I guess.
Regards,
Tvrtko
