Re: [Intel-gfx] [PATCH] drm/i915/mtl: Check full IP version when applying hw steering semaphore
On 05/12/2022 16:27, Matt Roper wrote:
On Mon, Dec 05, 2022 at 12:50:40PM +, 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
Fixes: 3100240bf846 ("drm/i915/mtl: Add hardware-level lock for steering")
Cc: Balasubramani Vivekanandan
Signed-off-by: Matt Roper
Reviewed-by: Rodrigo Vivi
---
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
Re: [Intel-gfx] [PATCH] drm/i915/mtl: Check full IP version when applying hw steering semaphore
On Mon, Dec 05, 2022 at 12:50:40PM +, 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
> > > Fixes: 3100240bf846 ("drm/i915/mtl: Add hardware-level lock for steering")
> > > Cc: Balasubramani Vivekanandan
> > > Signed-off-by: Matt Roper
> >
> > Reviewed-by: Rodrigo Vivi
> > > ---
> > > 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
Re: [Intel-gfx] [PATCH] drm/i915/mtl: Check full IP version when applying hw steering semaphore
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
Fixes: 3100240bf846 ("drm/i915/mtl: Add hardware-level lock for steering")
Cc: Balasubramani Vivekanandan
Signed-off-by: Matt Roper
Reviewed-by: Rodrigo Vivi
---
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?
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))
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
Re: [Intel-gfx] [PATCH] drm/i915/mtl: Check full IP version when applying hw steering semaphore
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
> Fixes: 3100240bf846 ("drm/i915/mtl: Add hardware-level lock for steering")
> Cc: Balasubramani Vivekanandan
> Signed-off-by: Matt Roper
Reviewed-by: Rodrigo Vivi
> ---
> 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))
> 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
>
[Intel-gfx] [PATCH] drm/i915/mtl: Check full IP version when applying hw steering semaphore
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
Fixes: 3100240bf846 ("drm/i915/mtl: Add hardware-level lock for steering")
Cc: Balasubramani Vivekanandan
Signed-off-by: Matt Roper
---
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))
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
