linux-kernel - Re: [PATCH] drm/i915: Enable digital port hotplug on PCH systems

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Date:	Tue, 20 Sep 2011 09:36:31 -0700
From:	Keith Packard <keithp@...thp.com>
To:	Chris Wilson <chris@...is-wilson.co.uk>,
	Dave Airlie <airlied@...hat.com>
Cc:	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/i915: Enable digital port hotplug on PCH systems

On Tue, 20 Sep 2011 17:24:21 +0100, Chris Wilson <chris@...is-wilson.co.uk> wrote:
> On Tue, 20 Sep 2011 08:47:21 -0700, Keith Packard <keithp@...thp.com> wrote:
> > We were relying on the BIOS to set these bits, which doesn't always
> > happen.
> 
> Do we need to clear IRQ bits on uninstall, for example to prevent
> "Interrupt 19: no one cared!" or is that due to a different cause?

Probably a good plan, but of course that's separate from turning on the
hotplug hardware in the PCH. Something like:

diff --git a/drivers/gpu/drm/i915/i915_irq.c b/drivers/gpu/drm/i915/i915_irq.c
index c22823b..adeab2a 100644
--- a/drivers/gpu/drm/i915/i915_irq.c
+++ b/drivers/gpu/drm/i915/i915_irq.c
@@ -2044,6 +2044,10 @@ static void ironlake_irq_uninstall(struct drm_device *dev)
 	I915_WRITE(GTIMR, 0xffffffff);
 	I915_WRITE(GTIER, 0x0);
 	I915_WRITE(GTIIR, I915_READ(GTIIR));
+
+	I915_WRITE(SDEIMR, 0xffffffff);
+	I915_WRITE(SDEIER, 0x0);
+	I915_WRITE(SDEIIR, I915_READ(SDEIIR));
 }
 
 static void i915_driver_irq_uninstall(struct drm_device * dev)

> More of a general question really. The patch itself looks good and
> matches against the spec afaics.

I was amused to learn that the BIOS on my machine actually turns on the
hotplug hardware for no good reason, so things 'worked' without this
code on many machines. I wonder how many DP/DVI/HDMI machines aren't
actually doing hotplug today...

-- 
keith.packard@...el.com

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