drm/radeon/kms: add module option for pcie gen2

Switching to pcie gen2 causes problems on some
boards.  Add a module option to turn it on/off.

There are gen2 compatability issues with some
motherboards it seems.

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=33027

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/evergreen.c

@@ -3158,6 +3158,9 @@ static void evergreen_pcie_gen2_enable(struct radeon_device *rdev)
 {
 	u32 link_width_cntl, speed_cntl;
 
+	if (radeon_pcie_gen2 == 0)
+		return;
+
 	if (rdev->flags & RADEON_IS_IGP)
 		return;
 

drivers/gpu/drm/radeon/r600.c

@@ -3658,6 +3658,9 @@ static void r600_pcie_gen2_enable(struct radeon_device *rdev)
 	u32 link_width_cntl, lanes, speed_cntl, training_cntl, tmp;
 	u16 link_cntl2;
 
+	if (radeon_pcie_gen2 == 0)
+		return;
+
 	if (rdev->flags & RADEON_IS_IGP)
 		return;
 

drivers/gpu/drm/radeon/radeon.h

@@ -92,6 +92,7 @@ extern int radeon_tv;
 extern int radeon_audio;
 extern int radeon_disp_priority;
 extern int radeon_hw_i2c;
+extern int radeon_pcie_gen2;
 
 /*
  * Copy from radeon_drv.h so we don't have to include both and have conflicting

drivers/gpu/drm/radeon/radeon_drv.c

@@ -104,6 +104,7 @@ int radeon_tv = 1;
 int radeon_audio = 1;
 int radeon_disp_priority = 0;
 int radeon_hw_i2c = 0;
+int radeon_pcie_gen2 = 0;
 
 MODULE_PARM_DESC(no_wb, "Disable AGP writeback for scratch registers");
 module_param_named(no_wb, radeon_no_wb, int, 0444);
@@ -147,6 +148,9 @@ module_param_named(disp_priority, radeon_disp_priority, int, 0444);
 MODULE_PARM_DESC(hw_i2c, "hw i2c engine enable (0 = disable)");
 module_param_named(hw_i2c, radeon_hw_i2c, int, 0444);
 
+MODULE_PARM_DESC(pcie_gen2, "PCIE Gen2 mode (1 = enable)");
+module_param_named(pcie_gen2, radeon_pcie_gen2, int, 0444);
+
 static int radeon_suspend(struct drm_device *dev, pm_message_t state)
 {
 	drm_radeon_private_t *dev_priv = dev->dev_private;

drivers/gpu/drm/radeon/rv770.c

@@ -1372,6 +1372,9 @@ static void rv770_pcie_gen2_enable(struct radeon_device *rdev)
 	u32 link_width_cntl, lanes, speed_cntl, tmp;
 	u16 link_cntl2;
 
+	if (radeon_pcie_gen2 == 0)
+		return;
+
 	if (rdev->flags & RADEON_IS_IGP)
 		return;