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path: root/i915-vga-arbiter.patch
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From 48be7e32f897277d77359e37db452281dd8b3bf8 Mon Sep 17 00:00:00 2001
From: Mark Weiman <mark.weiman@markzz.com>
Date: Tue, 8 Oct 2019 18:48:25 -0400
Subject: [PATCH] i915: Add module option to support VGA arbiter on HD devices
 (5.3)

This is an updated version of Alex Williamson's patch from:
https://lkml.org/lkml/2014/5/9/517
I don't have i915 graphics, so this is completely untested.

Original commit message follows:
---
Commit 81b5c7bc found that the current VGA arbiter support in i915
only works for ancient GMCH-based IGD devices and attempted to update
support for newer HD devices.  Unfortunately newer devices cannot
completely opt-out of VGA arbitration like the old devices could.
The VGA I/O space cannot be disabled internally.  The only way to
route VGA I/O elsewhere is by disabling I/O at the device PCI command
register.  This means that with commit 81b5c7bc and multiple VGA
adapters, the VGA arbiter will report that multiple VGA devices are
participating in arbitration, Xorg will notice this and disable DRI.
Therefore, 81b5c7bc was reverted because DRI is more important than
being correct.

There is however an actual need for i915 to correctly participate in
VGA arbitration; VGA device assignment.  If we want to use VFIO to
assign a VGA device to a virtual machine, we need to be able to
access the VGA resources of that device.  By adding an i915 module
option we can allow i915 to continue with its charade by default, but
also allow an easy path for users who require working VGA arbitration.
Hopefully Xorg can someday be taught to behave better with multiple
VGA devices.

This also rolls in reverted commit 6e1b4fda, which corrected an
ordering issue with 81b5c7bc by delaying the disabling of VGA memory
until after vgacon->fbcon handoff.
---
 drivers/gpu/drm/i915/display/intel_display.c | 34 +++++++++++++++++++++++++++++++++-
 drivers/gpu/drm/i915/display/intel_display.h |  1 +
 drivers/gpu/drm/i915/i915_drv.c              | 23 +++++++++++++++++++----
 drivers/gpu/drm/i915/i915_params.c           |  3 +++
 drivers/gpu/drm/i915/i915_params.h           |  1 +
 5 files changed, 57 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index af50f05f4..7c61721b4 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -15959,6 +15959,36 @@ static void i915_disable_vga(struct drm_i915_private *dev_priv)
 	POSTING_READ(vga_reg);
 }
 
+static void i915_enable_vga_mem(struct drm_i915_private *dev_priv)
+{
+	struct pci_dev *pdev = dev_priv->drm.pdev;
+
+	/* Enable VGA memory on Intel HD */
+	if (i915_modparams.enable_hd_vgaarb && HAS_PCH_SPLIT(dev_priv)) {
+		vga_get_uninterruptible(pdev, VGA_RSRC_LEGACY_IO);
+		outb(inb(VGA_MSR_READ) | VGA_MSR_MEM_EN, VGA_MSR_WRITE);
+		vga_set_legacy_decoding(pdev, VGA_RSRC_LEGACY_IO |
+						VGA_RSRC_LEGACY_MEM |
+						VGA_RSRC_NORMAL_IO |
+						VGA_RSRC_NORMAL_MEM);
+		vga_put(pdev, VGA_RSRC_LEGACY_IO);
+	}
+}
+
+void i915_disable_vga_mem(struct drm_i915_private *dev_priv)
+{
+	struct pci_dev *pdev = dev_priv->drm.pdev;
+	/* Disable VGA memory on Intel HD */
+	if (i915_modparams.enable_hd_vgaarb && HAS_PCH_SPLIT(dev_priv)) {
+		vga_get_uninterruptible(pdev, VGA_RSRC_LEGACY_IO);
+		outb(inb(VGA_MSR_READ) & ~VGA_MSR_MEM_EN, VGA_MSR_WRITE);
+		vga_set_legacy_decoding(pdev, VGA_RSRC_LEGACY_IO |
+						   VGA_RSRC_NORMAL_IO |
+						   VGA_RSRC_NORMAL_MEM);
+		vga_put(pdev, VGA_RSRC_LEGACY_IO);
+	}
+}
+
 void intel_modeset_init_hw(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = to_i915(dev);
@@ -16597,7 +16627,7 @@ void i915_redisable_vga_power_on(struct drm_i915_private *dev_priv)
 
 	if (!(I915_READ(vga_reg) & VGA_DISP_DISABLE)) {
 		DRM_DEBUG_KMS("Something enabled VGA plane, disabling it\n");
-		i915_disable_vga(dev_priv);
+		i915_disable_vga_mem(dev_priv);
 	}
 }
 
@@ -17091,6 +17121,8 @@ void intel_modeset_driver_remove(struct drm_device *dev)
 {
 	struct drm_i915_private *dev_priv = to_i915(dev);
 
+	i915_enable_vga_mem(dev_priv);
+
 	flush_workqueue(dev_priv->modeset_wq);
 
 	flush_work(&dev_priv->atomic_helper.free_work);
diff --git a/drivers/gpu/drm/i915/display/intel_display.h b/drivers/gpu/drm/i915/display/intel_display.h
index 01fa87ad3..ebcd9d52c 100644
--- a/drivers/gpu/drm/i915/display/intel_display.h
+++ b/drivers/gpu/drm/i915/display/intel_display.h
@@ -433,6 +433,7 @@ int vlv_get_cck_clock_hpll(struct drm_i915_private *dev_priv,
 			   const char *name, u32 reg);
 void lpt_disable_pch_transcoder(struct drm_i915_private *dev_priv);
 void lpt_disable_iclkip(struct drm_i915_private *dev_priv);
+extern void i915_disable_vga_mem(struct drm_i915_private *dev_priv);
 void intel_init_display_hooks(struct drm_i915_private *dev_priv);
 unsigned int intel_fb_xy_to_linear(int x, int y,
 				   const struct intel_plane_state *state,
diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 3d717e282..66eafc088 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -353,11 +353,20 @@ static int i915_driver_modeset_probe(struct drm_device *dev)
 	 * If we are a secondary display controller (!PCI_DISPLAY_CLASS_VGA),
 	 * then we do not take part in VGA arbitration and the
 	 * vga_client_register() fails with -ENODEV.
+	 *
+	 * NB. The set_decode callback here actually works on GMCH
+	 * devices, on newer HD devices we can only disable VGA MMIO space.
+	 * Disabling VGA I/O space requires disabling I/O in the PCI command
+	 * register.  Nonetheless, we like to pretend that we participate in
+	 * VGA arbitration and can dynamically disable VGA I/O space because
+	 * this makes X happy, even though it's a complete lie.
 	 */
-	ret = vga_client_register(pdev, dev_priv, NULL, i915_vga_set_decode);
-	if (ret && ret != -ENODEV)
-		goto out;
-
+	if (!i915_modparams.enable_hd_vgaarb || !HAS_PCH_SPLIT(dev_priv)) {
+		ret = vga_client_register(pdev, dev, NULL,
+					  i915_vga_set_decode);
+		if (ret && ret != -ENODEV)
+			goto out;
+	}
 	intel_register_dsm_handler();
 
 	ret = vga_switcheroo_register_client(pdev, &i915_switcheroo_ops, false);
@@ -393,6 +402,12 @@ static int i915_driver_modeset_probe(struct drm_device *dev)
 	if (ret)
 		goto cleanup_gem;
 
+	/*
+	 * Must do this after fbcon init so that
+	 * vgacon_save_screen() works during the handover.
+	 */
+	i915_disable_vga_mem(dev_priv);
+
 	/* Only enable hotplug handling once the fbdev is fully set up. */
 	intel_hpd_init(dev_priv);
 
diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
index 296452f9e..573c188fb 100644
--- a/drivers/gpu/drm/i915/i915_params.c
+++ b/drivers/gpu/drm/i915/i915_params.c
@@ -127,6 +127,9 @@ i915_param_named_unsafe(invert_brightness, int, 0600,
 i915_param_named(disable_display, bool, 0400,
 	"Disable display (default: false)");
 
+i915_param_named(enable_hd_vgaarb, bool, 0444,
+	"Enable support for VGA arbitration on Intel HD IGD. (default: false)");
+
 i915_param_named(mmio_debug, int, 0600,
 	"Enable the MMIO debug code for the first N failures (default: off). "
 	"This may negatively affect performance.");
diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
index d29ade3b7..f71498879 100644
--- a/drivers/gpu/drm/i915/i915_params.h
+++ b/drivers/gpu/drm/i915/i915_params.h
@@ -68,6 +68,7 @@ struct drm_printer;
 	param(char *, force_probe, CONFIG_DRM_I915_FORCE_PROBE) \
 	/* leave bools at the end to not create holes */ \
 	param(bool, alpha_support, IS_ENABLED(CONFIG_DRM_I915_ALPHA_SUPPORT)) \
+	param(bool, enable_hd_vgaarb, false) \
 	param(bool, enable_hangcheck, true) \
 	param(bool, prefault_disable, false) \
 	param(bool, load_detect_test, false) \
-- 
2.23.0