[PATCH] drm/i915: only disable default vga device

[Emil Velikov]

From: Vivek Das Mohapatra <vivek at collabora.com>

This patch is to do with seamless handover, eg when the sequence is
bootloader → plymouth → desktop.

It switches the vga arbiter from the "other" GPU to the default one
(intel in this case), so the driver can issue some io().

Signed-off-by: Vivek Das Mohapatra <vivek at collabora.com>
Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
---
Greetings all,

This patch has been downstream for a while now yet it seems perfectly
reasonable thing to have in the Linux kernel.

https://github.com/ValveSoftware/steamos_kernel/commit/5431b5b1999c3d3b5efee817fb3373fbbd473063


 drivers/gpu/drm/i915/display/intel_vga.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_vga.c b/drivers/gpu/drm/i915/display/intel_vga.c
index be333699c515..4f07b5ad5fa0 100644
--- a/drivers/gpu/drm/i915/display/intel_vga.c
+++ b/drivers/gpu/drm/i915/display/intel_vga.c
@@ -30,12 +30,14 @@ void intel_vga_disable(struct drm_i915_private *dev_priv)
 	u8 sr1;
 
 	/* WaEnableVGAAccessThroughIOPort:ctg,elk,ilk,snb,ivb,vlv,hsw */
-	vga_get_uninterruptible(pdev, VGA_RSRC_LEGACY_IO);
-	outb(SR01, VGA_SR_INDEX);
-	sr1 = inb(VGA_SR_DATA);
-	outb(sr1 | 1 << 5, VGA_SR_DATA);
-	vga_put(pdev, VGA_RSRC_LEGACY_IO);
-	udelay(300);
+	if (pdev == vga_default_device()) {
+		vga_get_uninterruptible(pdev, VGA_RSRC_LEGACY_IO);
+		outb(SR01, VGA_SR_INDEX);
+		sr1 = inb(VGA_SR_DATA);
+		outb(sr1 | 1 << 5, VGA_SR_DATA);
+		vga_put(pdev, VGA_RSRC_LEGACY_IO);
+		udelay(300);
+	}
 
 	intel_de_write(dev_priv, vga_reg, VGA_DISP_DISABLE);
 	intel_de_posting_read(dev_priv, vga_reg);
-- 
2.27.0