i915: Update VGA arbiter support for newer devices

This is intended to add VGA arbiter support for Intel HD graphics on
Core processors.  The old GMCH registers no longer exist, so even
though it appears that i915 participates in VGA arbitration, it doesn't
work.  On Intel HD graphics we already attempt to disable VGA regions
of the device.  This makes registering as a VGA client unnecessary since
we don't intend to operate differently depending on how many VGA devices
are present.  We can disable VGA memory regions by clearing the memory
enable bit in the VGA MSR.  That only leaves VGA IO, which we update
the VGA arbiter to know that we don't participate in VGA memory
arbitration.  We also add a hook on unload to re-enable memory and
reinstate VGA memory arbitration.

v3: Use explicit LEGACY_IO | LEGACY_MEM when restoring rather than
    LEGACY_MASK, per Ville's comments.

v2: I915_READ/WRITE accessors don't work in i915_disable_vga, use inb/outb
    directly.  Also, on the driver unbind VGA enable path, acquire legacy
    IO to re-enable VGA memory.  Correct comment.

Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
[danvet: Add patch changelog. Also squash in a fixup to have a dummy
static inline for vga_set_legacy_decoding for CONFIG_VGA_ARB=n as
reported by the 0-day kernel build bot.]
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

fixup 2

drivers/gpu/drm/i915/i915_dma.c

@@ -1290,9 +1290,12 @@ static int i915_load_modeset_init(struct drm_device *dev)
 	 * then we do not take part in VGA arbitration and the
 	 * vga_client_register() fails with -ENODEV.
 	 */
-	ret = vga_client_register(dev->pdev, dev, NULL, i915_vga_set_decode);
+	if (!HAS_PCH_SPLIT(dev)) {
+		ret = vga_client_register(dev->pdev, dev, NULL,
+					  i915_vga_set_decode);
 		if (ret && ret != -ENODEV)
 			goto out;
+	}
 
 	intel_register_dsm_handler();
 

drivers/gpu/drm/i915/intel_display.c

@@ -10041,6 +10041,15 @@ static void i915_disable_vga(struct drm_device *dev)
 	outb(SR01, VGA_SR_INDEX);
 	sr1 = inb(VGA_SR_DATA);
 	outb(sr1 | 1<<5, VGA_SR_DATA);
+
+	/* Disable VGA memory on Intel HD */
+	if (HAS_PCH_SPLIT(dev)) {
+		outb(inb(VGA_MSR_READ) & ~VGA_MSR_MEM_EN, VGA_MSR_WRITE);
+		vga_set_legacy_decoding(dev->pdev, VGA_RSRC_LEGACY_IO |
+						   VGA_RSRC_NORMAL_IO |
+						   VGA_RSRC_NORMAL_MEM);
+	}
+
 	vga_put(dev->pdev, VGA_RSRC_LEGACY_IO);
 	udelay(300);
 
@@ -10048,6 +10057,20 @@ static void i915_disable_vga(struct drm_device *dev)
 	POSTING_READ(vga_reg);
 }
 
+static void i915_enable_vga(struct drm_device *dev)
+{
+	/* Enable VGA memory on Intel HD */
+	if (HAS_PCH_SPLIT(dev)) {
+		vga_get_uninterruptible(dev->pdev, VGA_RSRC_LEGACY_IO);
+		outb(inb(VGA_MSR_READ) | VGA_MSR_MEM_EN, VGA_MSR_WRITE);
+		vga_set_legacy_decoding(dev->pdev, VGA_RSRC_LEGACY_IO |
+						   VGA_RSRC_LEGACY_MEM |
+						   VGA_RSRC_NORMAL_IO |
+						   VGA_RSRC_NORMAL_MEM);
+		vga_put(dev->pdev, VGA_RSRC_LEGACY_IO);
+	}
+}
+
 void intel_modeset_init_hw(struct drm_device *dev)
 {
 	intel_init_power_well(dev);
@@ -10539,6 +10562,8 @@ void intel_modeset_cleanup(struct drm_device *dev)
 
 	intel_disable_fbc(dev);
 
+	i915_enable_vga(dev);
+
 	intel_disable_gt_powersave(dev);
 
 	ironlake_teardown_rc6(dev);

include/linux/vgaarb.h

@@ -65,8 +65,15 @@ struct pci_dev;
  *     out of the arbitration process (and can be safe to take
  *     interrupts at any time.
  */
+#if defined(CONFIG_VGA_ARB)
 extern void vga_set_legacy_decoding(struct pci_dev *pdev,
 				    unsigned int decodes);
+#else
+static inline void vga_set_legacy_decoding(struct pci_dev *pdev,
+					   unsigned int decodes)
+{
+}
+#endif
 
 /**
  *     vga_get         - acquire & locks VGA resources