[Intel-gfx] [PATCH 8/8] drm/i915: fix hpd interrupt register locking

[Paulo Zanoni]

2013/6/27 Daniel Vetter <daniel.vetter at ffwll.ch>:
> Our interrupt handler (in hardird context) could race with the timer

s/hardird/hardirq/

> (in softirq context), hence we need to hold the spinlock around the
> call to ->hdp_irq_setup in intel_hpd_irq_handler, too.
>
> But as an optimization (and more so to clarify things) we don't need
> to do the irqsave/restore dance in the hardirq context.
>
> Note also that on ilk+ the race isn't just against the hotplug
> reenable timer, but also against the fifo underrun reporting. That one
> also modifies the SDEIMR register (again protected by the same
> dev_priv->irq_lock).
>
> To lock things down again sprinkle a assert_spin_locked. But exclude
> the functions touching SDEIMR for now, I want to extract them all into
> a new helper function (like we do already for pipestate, display
> interrupts and all the various gt interrupts).
>
> v2: Add the missing 't' Egbert spotted in a comment.
>
> Cc: Egbert Eich <eich at suse.de>
> Signed-off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
> ---
>  drivers/gpu/drm/i915/i915_irq.c | 17 +++++++++++------
>  1 file changed, 11 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> index 95999bc..6637575 100644
> --- a/drivers/gpu/drm/i915/i915_irq.c
> +++ b/drivers/gpu/drm/i915/i915_irq.c
> @@ -881,15 +881,13 @@ static inline void intel_hpd_irq_handler(struct drm_device *dev,
>                                          const u32 *hpd)
>  {
>         drm_i915_private_t *dev_priv = dev->dev_private;
> -       unsigned long irqflags;
>         int i;
>         bool storm_detected = false;
>
>         if (!hotplug_trigger)
>                 return;
>
> -       spin_lock_irqsave(&dev_priv->irq_lock, irqflags);
> -
> +       spin_lock(&dev_priv->irq_lock);
>         for (i = 1; i < HPD_NUM_PINS; i++) {
>
>                 if (!(hpd[i] & hotplug_trigger) ||
> @@ -912,10 +910,9 @@ static inline void intel_hpd_irq_handler(struct drm_device *dev,
>                 }
>         }
>
> -       spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
> -
>         if (storm_detected)
>                 dev_priv->display.hpd_irq_setup(dev);
> +       spin_unlock(&dev_priv->irq_lock);
>
>         queue_work(dev_priv->wq,
>                    &dev_priv->hotplug_work);
> @@ -2851,7 +2848,7 @@ static int valleyview_irq_postinstall(struct drm_device *dev)
>         I915_WRITE(PIPESTAT(1), 0xffff);
>         POSTING_READ(VLV_IER);
>
> -       /* Interrup setup is already guaranteed to be single-threaded, this is
> +       /* Interrupt setup is already guaranteed to be single-threaded, this is

Here you're fixing an error introduced in patch 03, instead of the
error pointed by Egbert.

>          * just to make the assert_spin_locked check happy. */
>         spin_lock_irqsave(&dev_priv->irq_lock, irqflags);
>         i915_enable_pipestat(dev_priv, 0, pipestat_enable);
> @@ -3395,6 +3392,8 @@ static void i915_hpd_irq_setup(struct drm_device *dev)
>         struct intel_encoder *intel_encoder;
>         u32 hotplug_en;
>
> +       assert_spin_locked(&dev_priv->irq_lock);
> +
>         if (I915_HAS_HOTPLUG(dev)) {
>                 hotplug_en = I915_READ(PORT_HOTPLUG_EN);
>                 hotplug_en &= ~HOTPLUG_INT_EN_MASK;
> @@ -3678,6 +3677,7 @@ void intel_hpd_init(struct drm_device *dev)
>         struct drm_i915_private *dev_priv = dev->dev_private;
>         struct drm_mode_config *mode_config = &dev->mode_config;
>         struct drm_connector *connector;
> +       unsigned long irqflags;
>         int i;
>
>         for (i = 1; i < HPD_NUM_PINS; i++) {
> @@ -3690,6 +3690,11 @@ void intel_hpd_init(struct drm_device *dev)
>                 if (!connector->polled && I915_HAS_HOTPLUG(dev) && intel_connector->encoder->hpd_pin > HPD_NONE)
>                         connector->polled = DRM_CONNECTOR_POLL_HPD;
>         }
> +
> +       /* Interrup setup is already guaranteed to be single-threaded, this is

s/Interrup/Interrupt/



> +        * just to make the assert_spin_locked checks happy. */
> +       spin_lock_irqsave(&dev_priv->irq_lock, irqflags);
>         if (dev_priv->display.hpd_irq_setup)
>                 dev_priv->display.hpd_irq_setup(dev);
> +       spin_unlock_irqrestore(&dev_priv->irq_lock, irqflags);
>  }
> --
> 1.8.1.4
>

So here's the review status for the 8 patches resent today:
- Patches 1 and 2: Reviewed-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
- Patch 3: in two comments you need to s/Interrup/Interrupt/. Then you
can add Reviewed-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
- Patches 4-7: You already have my Reviewed-by, but if you look in the
commit messages, some lines contain just my name and email, without
the "Reviewed-by:" text before them. I also wouldn't mind if you
resend patches 6 and 7 based on Chris's comments, but I don't really
care since the problem is actually solved in patch 7.
- Patch 8: due to the change you'll do in patch 3, you'll have to redo
patch 8. If you fix both the "Interrup" and the "hardird" typo you can
also add Reviewed-by: Paulo Zanoni <paulo.r.zanoni at intel.com>

I also booted a Haswell with these new patches and after 120 seconds
of uptime I don't see any new WARNs or ERRORs.

-- 
Paulo Zanoni