On Fri, 2023-12-01 at 12:00 +0200, 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.
>
> Cc: Tvrtko Ursulin <tvrto.ursulin@xxxxxxxxx>
> Cc: Jani Nikula <jani.nikula@xxxxxxxxx>
> Cc: Ville Syrjala <ville.syrjala@xxxxxxxxxxxxxxx>
> Cc: Rodrigo Vivi <rodrigo.vivi@xxxxxxxxx>
> Signed-off-by: Luca Coelho <luciano.coelho@xxxxxxxxx>
> ---
>
>
> 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.
>
> In v4:
>
> * After a brief attempt to replace this with a different patch,
> we're back to this one;
> * Pass drm_i195_private again, and move the functions to
> intel_vblank.c, so we don't need to include i915_drv.h in a
> header file and it's already included in intel_vblank.c;
>
> In v5:
>
> * Remove stray include in intel_display.h;
> * Remove unnecessary inline modifiers in the new functions.
>
> In v6:
>
> * Just removed the umlauts from Ville's name, because patchwork
> didn't catch my patch and I suspect it was some UTF-8 confusion.
>
> In v7:
>
> * Add __acquires()/__releases() annotation to resolve sparse
> warnings.
>
> drivers/gpu/drm/i915/display/intel_vblank.c | 51 +++++++++++++++++--
> --
> 1 file changed, 41 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_vblank.c
> b/drivers/gpu/drm/i915/display/intel_vblank.c
> index 2cec2abf9746..fe256bf7b485 100644
> --- a/drivers/gpu/drm/i915/display/intel_vblank.c
> +++ b/drivers/gpu/drm/i915/display/intel_vblank.c
> @@ -265,6 +265,32 @@ int intel_crtc_scanline_to_hw(struct intel_crtc
> *crtc, int scanline)
> return (scanline + vtotal - crtc->scanline_offset) % vtotal;
> }
>
> +/*
> + * 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.
> + *
> + * This lock in i915 is needed because some old platforms (at least
> + * IVB and possibly HSW as well), which are not supported in Xe,
> need
> + * all register accesses to the same cacheline to be serialized,
> + * otherwise they may hang.
> + */
> +static void intel_vblank_section_enter(struct drm_i915_private
> *i915)
> + __acquires(i915->uncore.lock)
> +{
> +#ifdef I915
> + spin_lock(&i915->uncore.lock);
> +#endif
> +}
> +
> +static void intel_vblank_section_exit(struct drm_i915_private *i915)
> + __releases(i915->uncore.lock)
> +{
> +#ifdef I915
> + spin_unlock(&i915->uncore.lock);
> +#endif
> +}
> +
Why don't you move these into gpu/drm/i915/intel_uncore.c/h? Then you
could have empty defines/functions for these in gpu/drm/xe/compat-i915-
headers/intel_uncore.h. That way you don't need these ifdefs. If you
move them as I proposed you should rename them as well.
BR,
Jouni Högander
> static bool i915_get_crtc_scanoutpos(struct drm_crtc *_crtc,
> bool in_vblank_irq,
> int *vpos, int *hpos,
> @@ -302,11 +328,12 @@ static bool i915_get_crtc_scanoutpos(struct
> drm_crtc *_crtc,
> }
>
> /*
> - * Lock uncore.lock, as we will do multiple timing critical
> raw
> - * register reads, potentially with preemption disabled, so
> the
> - * following code must not block on uncore.lock.
> + * Enter vblank critical section, as we will do multiple
> + * timing critical raw register reads, potentially with
> + * preemption disabled, so the following code must not block.
> */
> - spin_lock_irqsave(&dev_priv->uncore.lock, irqflags);
> + local_irq_save(irqflags);
> + intel_vblank_section_enter(dev_priv);
>
> /* preempt_disable_rt() should go right here in PREEMPT_RT
> patchset. */
>
> @@ -374,7 +401,8 @@ 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_vblank_section_exit(dev_priv);
> + local_irq_restore(irqflags);
>
> /*
> * While in vblank, position will be negative
> @@ -412,9 +440,13 @@ 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_vblank_section_enter(dev_priv);
> +
> position = __intel_get_crtc_scanline(crtc);
> - spin_unlock_irqrestore(&dev_priv->uncore.lock, irqflags);
> +
> + intel_vblank_section_exit(dev_priv);
> + local_irq_restore(irqflags);
>
> return position;
> }
> @@ -537,7 +569,7 @@ 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_vblank_section_enter(i915);
>
> drm_calc_timestamping_constants(&crtc->base, &adjusted_mode);
>
> @@ -546,7 +578,6 @@ 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_vblank_section_exit(i915);
> spin_unlock_irqrestore(&i915->drm.vblank_time_lock,
> irqflags);
> }
