[Intel-gfx] [PATCH] drm/intel: Only smash VGA SR01 register if intel is default VGA device

[Keith Packard]

We want to disable the (unused) VGA plane on the intel hardware, which
should be a simple matter of writing the vga control register. However,
in 2009 (commit 24f119c769bacac5729297b682fec7811a983cc6), that simple
code was changed to also smash the SR01 VGA register to fix "random
crash and lockups".

When running efifb on an nVidia card, executing this store to SR01
ends up causing the screen to go black.

I'm not sure if this store is still required; this patch limits it to
when the intel card is primary.

Signed-off-by: Keith Packard <keithp at keithp.com>
---

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

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index c714d4d..545b271 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -9038,12 +9038,14 @@ static void i915_disable_vga(struct drm_device *dev)
 	u8 sr1;
 	u32 vga_reg = i915_vgacntrl_reg(dev);
 
-	vga_get_uninterruptible(dev->pdev, VGA_RSRC_LEGACY_IO);
-	outb(SR01, VGA_SR_INDEX);
-	sr1 = inb(VGA_SR_DATA);
-	outb(sr1 | 1<<5, VGA_SR_DATA);
-	vga_put(dev->pdev, VGA_RSRC_LEGACY_IO);
-	udelay(300);
+	if (dev->pdev == vga_default_device()) {
+		vga_get_uninterruptible(dev->pdev, VGA_RSRC_LEGACY_IO);
+		outb(SR01, VGA_SR_INDEX);
+		sr1 = inb(VGA_SR_DATA);
+		outb(sr1 | 1<<5, VGA_SR_DATA);
+		vga_put(dev->pdev, VGA_RSRC_LEGACY_IO);
+		udelay(300);
+	}
 
 	I915_WRITE(vga_reg, VGA_DISP_DISABLE);
 	POSTING_READ(vga_reg);
-- 
1.8.5.1