drm/i915/display: Created exclusive version of vga decode setup

Current vga arbiter implementation in i915 needs a re-design.
The current approach would cause real problems if anyone actually
needs to talk another GPU using legacy VGA resources.

The main issue is that X becomes a slideshow if it thinks there
are multiple GPUs that have VGA decoding enabled as it insists
on adjusting the VGA routing pretty much for every little operation
involving any of the GPUs.

The cleanup will be planned for i915. Meanwhile to focus on Xe
upstreaming and have a cleaner separation, the said functionality
is being moved to a different file exclusive for i915. Xe driver
will re-use rest of the display code from i915.

v2: Addressed Jani Nikula's review comments.

v3: Dropped a duplicate function (Jani)

v4: Updated commit message with reasoning as sugested by Ville.
Signed-off-by: Uma Shankar <uma.shankar@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230929074306.1533859-1-uma.shankar@intel.com

drivers/gpu/drm/i915/display/intel_vga.c

@@ -3,11 +3,9 @@
  * Copyright © 2019 Intel Corporation
  */
 
-#include <linux/pci.h>
 #include <linux/vgaarb.h>
 
 #include <video/vga.h>
-
 #include "soc/intel_gmch.h"
 
 #include "i915_drv.h"
@@ -99,20 +97,6 @@ void intel_vga_reset_io_mem(struct drm_i915_private *i915)
 	vga_put(pdev, VGA_RSRC_LEGACY_IO);
 }
 
-static unsigned int
-intel_vga_set_decode(struct pci_dev *pdev, bool enable_decode)
-{
-	struct drm_i915_private *i915 = pdev_to_i915(pdev);
-
-	intel_gmch_vga_set_state(i915, enable_decode);
-
-	if (enable_decode)
-		return VGA_RSRC_LEGACY_IO | VGA_RSRC_LEGACY_MEM |
-		       VGA_RSRC_NORMAL_IO | VGA_RSRC_NORMAL_MEM;
-	else
-		return VGA_RSRC_NORMAL_IO | VGA_RSRC_NORMAL_MEM;
-}
-
 int intel_vga_register(struct drm_i915_private *i915)
 {
 
@@ -127,7 +111,7 @@ int intel_vga_register(struct drm_i915_private *i915)
 	 * then we do not take part in VGA arbitration and the
 	 * vga_client_register() fails with -ENODEV.
 	 */
-	ret = vga_client_register(pdev, intel_vga_set_decode);
+	ret = vga_client_register(pdev, intel_gmch_vga_set_decode);
 	if (ret && ret != -ENODEV)
 		return ret;
 

drivers/gpu/drm/i915/soc/intel_gmch.c

@@ -5,6 +5,7 @@
 
 #include <linux/pci.h>
 #include <linux/pnp.h>
+#include <linux/vgaarb.h>
 
 #include <drm/drm_managed.h>
 #include <drm/i915_drm.h>
@@ -167,3 +168,16 @@ int intel_gmch_vga_set_state(struct drm_i915_private *i915, bool enable_decode)
 
 	return 0;
 }
+
+unsigned int intel_gmch_vga_set_decode(struct pci_dev *pdev, bool enable_decode)
+{
+	struct drm_i915_private *i915 = pdev_to_i915(pdev);
+
+	intel_gmch_vga_set_state(i915, enable_decode);
+
+	if (enable_decode)
+		return VGA_RSRC_LEGACY_IO | VGA_RSRC_LEGACY_MEM |
+		       VGA_RSRC_NORMAL_IO | VGA_RSRC_NORMAL_MEM;
+	else
+		return VGA_RSRC_NORMAL_IO | VGA_RSRC_NORMAL_MEM;
+}

drivers/gpu/drm/i915/soc/intel_gmch.h

@@ -8,11 +8,13 @@
 
 #include <linux/types.h>
 
+struct pci_dev;
 struct drm_i915_private;
 
 int intel_gmch_bridge_setup(struct drm_i915_private *i915);
 void intel_gmch_bar_setup(struct drm_i915_private *i915);
 void intel_gmch_bar_teardown(struct drm_i915_private *i915);
 int intel_gmch_vga_set_state(struct drm_i915_private *i915, bool enable_decode);
+unsigned int intel_gmch_vga_set_decode(struct pci_dev *pdev, bool enable_decode);
 
 #endif /* __INTEL_GMCH_H__ */