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The hardware provides a > dedicated locking mechanism to support this via the MTL_STEER_SEMAPHORE > register. Reading the register acts as a 'trylock' operation; the read > will return 0x1 if the lock is acquired or 0x0 if something else is > already holding the lock; once acquired, writing 0x1 to the register > will release the lock. > > We'll continue to grab the software lock as well, just so lockdep can > track our locking; assuming the hardware lock is behaving properly, > there should never be any contention on the software lock in this case. > > v2: > - Extend hardware semaphore timeout and add a taint for CI if it ever > happens (this would imply misbehaving hardware/firmware). (Mika) > - Add "MTL_" prefix to new steering semaphore register. (Mika) > > Cc: Mika Kuoppala > Signed-off-by: Matt Roper Reviewed-by: Balasubramani Vivekanandan Regards, Bala > --- > drivers/gpu/drm/i915/gt/intel_gt_mcr.c | 38 ++++++++++++++++++++++--- > drivers/gpu/drm/i915/gt/intel_gt_regs.h | 1 + > 2 files changed, 35 insertions(+), 4 deletions(-) > > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c > index aa070ae57f11..087e4ac5b68d 100644 > --- a/drivers/gpu/drm/i915/gt/intel_gt_mcr.c > +++ b/drivers/gpu/drm/i915/gt/intel_gt_mcr.c > @@ -347,10 +347,9 @@ static u32 rw_with_mcr_steering(struct intel_gt *gt, > * @flags: storage to save IRQ flags to > * > * Performs locking to protect the steering for the duration of an MCR > - * operation. Depending on the platform, this may be a software lock > - * (gt->mcr_lock) or a hardware lock (i.e., a register that synchronizes > - * access not only for the driver, but also for external hardware and > - * firmware agents). > + * operation. On MTL and beyond, a hardware lock will also be taken to > + * serialize access not only for the driver, but also for external hardware and > + * firmware agents. > * > * Context: Takes gt->mcr_lock. uncore->lock should *not* be held when this > * function is called, although it may be acquired after this > @@ -359,12 +358,40 @@ static u32 rw_with_mcr_steering(struct intel_gt *gt, > void intel_gt_mcr_lock(struct intel_gt *gt, unsigned long *flags) > { > unsigned long __flags; > + int err = 0; > > lockdep_assert_not_held(>->uncore->lock); > > + /* > + * Starting with MTL, we need to coordinate not only with other > + * driver threads, but also with hardware/firmware agents. A dedicated > + * locking register is used. > + */ > + if (GRAPHICS_VER(gt->i915) >= IP_VER(12, 70)) > + err = wait_for(intel_uncore_read_fw(gt->uncore, > + MTL_STEER_SEMAPHORE) == 0x1, 100); > + > + /* > + * Even on platforms with a hardware lock, we'll continue to grab > + * a software spinlock too for lockdep purposes. If the hardware lock > + * was already acquired, there should never be contention on the > + * software lock. > + */ > spin_lock_irqsave(>->mcr_lock, __flags); > > *flags = __flags; > + > + /* > + * In theory we should never fail to acquire the HW semaphore; this > + * would indicate some hardware/firmware is misbehaving and not > + * releasing it properly. > + */ > + if (err == -ETIMEDOUT) { > + drm_err_ratelimited(>->i915->drm, > + "GT%u hardware MCR steering semaphore timed out", > + gt->info.id); > + add_taint_for_CI(gt->i915, TAINT_WARN); /* CI is now unreliable */ > + } > } > > /** > @@ -379,6 +406,9 @@ void intel_gt_mcr_lock(struct intel_gt *gt, unsigned long *flags) > 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)) > + intel_uncore_write_fw(gt->uncore, MTL_STEER_SEMAPHORE, 0x1); > } > > /** > diff --git a/drivers/gpu/drm/i915/gt/intel_gt_regs.h b/drivers/gpu/drm/i915/gt/intel_gt_regs.h > index 784152548472..1618d46cb8c7 100644 > --- a/drivers/gpu/drm/i915/gt/intel_gt_regs.h > +++ b/drivers/gpu/drm/i915/gt/intel_gt_regs.h > @@ -67,6 +67,7 @@ > #define GMD_ID_MEDIA _MMIO(MTL_MEDIA_GSI_BASE + 0xd8c) > > #define MCFG_MCR_SELECTOR _MMIO(0xfd0) > +#define MTL_STEER_SEMAPHORE _MMIO(0xfd0) > #define MTL_MCR_SELECTOR _MMIO(0xfd4) > #define SF_MCR_SELECTOR _MMIO(0xfd8) > #define GEN8_MCR_SELECTOR _MMIO(0xfdc) > -- > 2.38.1 >