drm/radeon/kms: add MSI module parameter

Allow the user to override whether MSIs are enabled
or not on supported ASICs.  MSIs are disabled by default
on IGP chips as they tend not to work.  However certain
IGP chips only seem to work with MSIs enabled.

I suspect this is a chipset or bios issue, but I'm not sure
what the proper fix is.  This will at least make diagnosing
and working around the problem much easier.

See:
https://bugs.freedesktop.org/show_bug.cgi?id=37679

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon.h

@@ -93,6 +93,7 @@ extern int radeon_audio;
 extern int radeon_disp_priority;
 extern int radeon_hw_i2c;
 extern int radeon_pcie_gen2;
+extern int radeon_msi;
 
 /*
  * Copy from radeon_drv.h so we don't have to include both and have conflicting

drivers/gpu/drm/radeon/radeon_drv.c

@@ -118,6 +118,7 @@ int radeon_audio = 0;
 int radeon_disp_priority = 0;
 int radeon_hw_i2c = 0;
 int radeon_pcie_gen2 = 0;
+int radeon_msi = -1;
 
 MODULE_PARM_DESC(no_wb, "Disable AGP writeback for scratch registers");
 module_param_named(no_wb, radeon_no_wb, int, 0444);
@@ -164,6 +165,9 @@ 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);
 
+MODULE_PARM_DESC(msi, "MSI support (1 = enable, 0 = disable, -1 = auto)");
+module_param_named(msi, radeon_msi, 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/radeon_irq_kms.c

@@ -118,6 +118,12 @@ static bool radeon_msi_ok(struct radeon_device *rdev)
 	if (rdev->flags & RADEON_IS_AGP)
 		return false;
 
+	/* force MSI on */
+	if (radeon_msi == 1)
+		return true;
+	else if (radeon_msi == 0)
+		return false;
+
 	/* Quirks */
 	/* HP RS690 only seems to work with MSIs. */
 	if ((rdev->pdev->device == 0x791f) &&