Re: [PATCH] drm/i915: add hotplug activation period to hotplug update mask

Daniel Vetter
2015-10-22T08:03:57Z

On Thu, Oct 22, 2015 at 10:46:58AM +0300, Jani Nikula wrote:
> On Wed, 21 Oct 2015, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> > On Wed, Oct 21, 2015 at 05:22:43PM +0300, Jani Nikula wrote:
> >> commit 0706f17c307b056ff6f1848320ba82d76945a6ff
> >> Author: Egbert Eich <eich@suse.de>
> >> Date: Wed Sep 23 16:15:27 2015 +0200
> >>
> >> drm/i915: Avoid race of intel_crt_detect_hotplug() with HPD interrupt, v2
> >>
> >> added a check with WARN to ensure only bits within the mask are
> >> enabled. Turns out that doesn't hold for G4X, which spits out:
> >>
> >> [ 2.641439] ------------[ cut here ]------------
> >> [ 2.641444] WARNING: CPU: 0 PID: 1 at drivers/gpu/drm/i915/i915_irq.c:182 i915_hotplug_interrupt_update_locked+0x45/0x83()
> >> [ 2.641446] WARN_ON(bits & ~mask)
> >> etc.
> >>
> >> Add CRT_HOTPLUG_ACTIVATION_PERIOD_64 to the mask to fix the warning.
> >>
> >> Reported-by: Oleksij Rempel <linux@rempel-privat.de>
> >> References: https://bugzilla.kernel.org/show_bug.cgi?id=104991
> >> Fixes: 0706f17c307b ("drm/i915: Avoid race of intel_crt_detect_hotplug() with HPD interrupt, v2")
> >> Cc: Egbert Eich <eich@suse.de>
> >> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> >> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
> >> ---
> >> drivers/gpu/drm/i915/i915_irq.c | 7 ++++---
> >> 1 file changed, 4 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
> >> index 7f91f74961f4..5b9f63d4318b 100644
> >> --- a/drivers/gpu/drm/i915/i915_irq.c
> >> +++ b/drivers/gpu/drm/i915/i915_irq.c
> >> @@ -4236,9 +4236,10 @@ static void i915_hpd_irq_setup(struct drm_device *dev)
> >>
> >> /* Ignore TV since it's buggy */
> >> i915_hotplug_interrupt_update_locked(dev_priv,
> >> - (HOTPLUG_INT_EN_MASK
> >> - | CRT_HOTPLUG_VOLTAGE_COMPARE_MASK),
> >> - hotplug_en);
> >> + HOTPLUG_INT_EN_MASK |
> >> + CRT_HOTPLUG_VOLTAGE_COMPARE_MASK |
> >> + CRT_HOTPLUG_ACTIVATION_PERIOD_64,
> >> + hotplug_en);
> >
> > Or maybe just ~CRT_HOTPLUG_FORCE_DETECT ?
>
> This patch already potentially changes behaviour by explicitly setting
> the activation period to zero (CRT_HOTPLUG_ACTIVATION_PERIOD_32) on
> non-g4x. Previously it was "don't care". Call me coward, but I am not
> comfortable with setting the rest of the bits to zero, at least not in
> the context of this fix, and risking regressions on old machines.

Might be a notch too paranoid, but we've always had that rmw in there.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

>
> BR,
> Jani.
>
>
> >
> >> }
> >>
> >> static irqreturn_t i965_irq_handler(int irq, void *arg)
> >> --
> >> 2.1.4
> >>
> >> _______________________________________________
> >> Intel-gfx mailing list
> >> Intel-gfx@lists.freedesktop.org
> >> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
> >
> > --
> > Ville Syrjälä
> > Intel OTC
>
> --
> Jani Nikula, Intel Open Source Technology Center

--
Daniel Vetter
Software Engineer, Intel Corporation