drm/i915: touch VGA MSR after we enable the power well

[mirror_ubuntu-bionic-kernel.git] / drivers / gpu / drm / i915 / intel_pm.c

diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
index d8fb00a2b56549df388654c964cec186fb069686..3cd521f3823bb8e7c547874b4a6b12e929c5312e 100644 (file)
--- a/drivers/gpu/drm/i915/intel_pm.c
+++ b/drivers/gpu/drm/i915/intel_pm.c
@@ -30,6 +30,7 @@
 #include "intel_drv.h"
 #include "../../../platform/x86/intel_ips.h"
 #include <linux/module.h>
+#include <linux/vgaarb.h>
 #include <drm/i915_powerwell.h>
 #include <linux/pm_runtime.h>
 
@@ -5686,6 +5687,20 @@ static void hsw_power_well_post_enable(struct drm_i915_private *dev_priv)
        struct drm_device *dev = dev_priv->dev;
        unsigned long irqflags;
 
+       /*
+        * After we re-enable the power well, if we touch VGA register 0x3d5
+        * we'll get unclaimed register interrupts. This stops after we write
+        * anything to the VGA MSR register. The vgacon module uses this
+        * register all the time, so if we unbind our driver and, as a
+        * consequence, bind vgacon, we'll get stuck in an infinite loop at
+        * console_unlock(). So make here we touch the VGA MSR register, making
+        * sure vgacon can keep working normally without triggering interrupts
+        * and error messages.
+        */
+       vga_get_uninterruptible(dev->pdev, VGA_RSRC_LEGACY_IO);
+       outb(inb(VGA_MSR_READ), VGA_MSR_WRITE);
+       vga_put(dev->pdev, VGA_RSRC_LEGACY_IO);
+
        if (IS_BROADWELL(dev)) {
                spin_lock_irqsave(&dev_priv->irq_lock, irqflags);
                I915_WRITE(GEN8_DE_PIPE_IMR(PIPE_B),