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25 Oct 2023 03:25:06 -0700 Message-ID: <463b540d-fd0d-4988-9ad1-63447a5d6948@linux.intel.com> Date: Wed, 25 Oct 2023 11:25:04 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Content-Language: en-US From: Tvrtko Ursulin To: Luca Coelho , intel-gfx@lists.freedesktop.org References: <20231023103328.1495942-1-luciano.coelho@intel.com> Organization: Intel Corporation UK Plc In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Subject: Re: [Intel-gfx] [PATCH v3] drm/i915: handle uncore spinlock when not available X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: intel-xe@lists.freedesktop.org, rodrigo.vivi@intel.com Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" On 25/10/2023 11:18, Tvrtko Ursulin wrote: > > On 23/10/2023 11:33, Luca Coelho wrote: >> The uncore code may not always be available (e.g. when we build the >> display code with Xe), so we can't always rely on having the uncore's >> spinlock. >> >> To handle this, split the spin_lock/unlock_irqsave/restore() into >> spin_lock/unlock() followed by a call to local_irq_save/restore() and >> create wrapper functions for locking and unlocking the uncore's >> spinlock.  In these functions, we have a condition check and only >> actually try to lock/unlock the spinlock when I915 is defined, and >> thus uncore is available. >> >> This keeps the ifdefs contained in these new functions and all such >> logic inside the display code. >> >> Signed-off-by: Luca Coelho >> --- >> >> In v2: >> >>     * Renamed uncore_spin_*() to intel_spin_*() >>     * Corrected the order: save, lock, unlock, restore >> >> In v3: >> >>     * Undid the change to pass drm_i915_private instead of the lock >>       itself, since we would have to include i915_drv.h and that pulls >>       in a truckload of other includes. >> >>   drivers/gpu/drm/i915/display/intel_display.h | 20 ++++++++++++++++++++ >>   drivers/gpu/drm/i915/display/intel_vblank.c  | 19 ++++++++++++------- >>   2 files changed, 32 insertions(+), 7 deletions(-) >> >> diff --git a/drivers/gpu/drm/i915/display/intel_display.h >> b/drivers/gpu/drm/i915/display/intel_display.h >> index 0e5dffe8f018..2a33fcc8ce68 100644 >> --- a/drivers/gpu/drm/i915/display/intel_display.h >> +++ b/drivers/gpu/drm/i915/display/intel_display.h >> @@ -559,4 +559,24 @@ bool assert_port_valid(struct drm_i915_private >> *i915, enum port port); >>   bool intel_scanout_needs_vtd_wa(struct drm_i915_private *i915); >> +/* >> + * The uncore version of the spin lock functions is used to decide >> + * whether we need to lock the uncore lock or not.  This is only >> + * needed in i915, not in Xe.  Keep the decision-making centralized >> + * here. >> + */ >> +static inline void intel_spin_lock(spinlock_t *lock) >> +{ >> +#ifdef I915 >> +    spin_lock(lock); >> +#endif >> +} >> + >> +static inline void intel_spin_unlock(spinlock_t *lock) >> +{ >> +#ifdef I915 >> +    spin_unlock(lock); >> +#endif >> +} >> + >>   #endif >> diff --git a/drivers/gpu/drm/i915/display/intel_vblank.c >> b/drivers/gpu/drm/i915/display/intel_vblank.c >> index 2cec2abf9746..9b482d648762 100644 >> --- a/drivers/gpu/drm/i915/display/intel_vblank.c >> +++ b/drivers/gpu/drm/i915/display/intel_vblank.c >> @@ -306,7 +306,8 @@ static bool i915_get_crtc_scanoutpos(struct >> drm_crtc *_crtc, >>        * register reads, potentially with preemption disabled, so the >>        * following code must not block on uncore.lock. >>        */ >> -    spin_lock_irqsave(&dev_priv->uncore.lock, irqflags); >> +    local_irq_save(irqflags); > > Does Xe needs interrupts off? > >> +    intel_spin_lock(&dev_priv->uncore.lock); > > My 2p/c is that intel_spin_lock as a name does not work when it is > specifically about the single and specific (uncore) lock. One cannot > call intel_spin_lock(some->other->lock) etc. > > Perhaps call it i915_uncore_lock_irqsave(i915, flags) so it is clear it > is only for i915. Or, if the implementation will later gain the #else block for Xe, perhaps intel_uncore_lock_...? Regards, Tvrtko >>       /* preempt_disable_rt() should go right here in PREEMPT_RT >> patchset. */ >> @@ -374,7 +375,8 @@ static bool i915_get_crtc_scanoutpos(struct >> drm_crtc *_crtc, >>       /* preempt_enable_rt() should go right here in PREEMPT_RT >> patchset. */ >> -    spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags); >> +    intel_spin_unlock(&dev_priv->uncore.lock); >> +    local_irq_restore(irqflags); >>       /* >>        * While in vblank, position will be negative >> @@ -412,9 +414,13 @@ int intel_get_crtc_scanline(struct intel_crtc *crtc) >>       unsigned long irqflags; >>       int position; >> -    spin_lock_irqsave(&dev_priv->uncore.lock, irqflags); >> +    local_irq_save(irqflags); >> +    intel_spin_lock(&dev_priv->uncore.lock); >> + >>       position = __intel_get_crtc_scanline(crtc); >> -    spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags); >> + >> +    intel_spin_unlock(&dev_priv->uncore.lock); >> +    local_irq_restore(irqflags); >>       return position; >>   } >> @@ -537,7 +543,7 @@ void intel_crtc_update_active_timings(const struct >> intel_crtc_state *crtc_state, >>        * Need to audit everything to make sure it's safe. >>        */ >>       spin_lock_irqsave(&i915->drm.vblank_time_lock, irqflags); >> -    spin_lock(&i915->uncore.lock); >> +    intel_spin_lock(&i915->uncore.lock); >>       drm_calc_timestamping_constants(&crtc->base, &adjusted_mode); >> @@ -546,7 +552,6 @@ void intel_crtc_update_active_timings(const struct >> intel_crtc_state *crtc_state, >>       crtc->mode_flags = mode_flags; >>       crtc->scanline_offset = intel_crtc_scanline_offset(crtc_state); >> - >> -    spin_unlock(&i915->uncore.lock); >> +    intel_spin_unlock(&i915->uncore.lock); >>       spin_unlock_irqrestore(&i915->drm.vblank_time_lock, irqflags); >>   }