linux-vfio/i915-vga-arbiter.patch

From 07af9476bf0b340df883f558a5c5c1ecad05b406 Mon Sep 17 00:00:00 2001
From: Mark King <mweiman@merit.edu>
Date: Thu, 29 Sep 2022 10:30:20 -0400
Subject: [PATCH] i915: Add module option to support VGA arbiter on HD devices
 (5.19)

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 | 15 ++++++++--
 drivers/gpu/drm/i915/display/intel_display.h |  1 +
 drivers/gpu/drm/i915/display/intel_vga.c     | 31 ++++++++++++++++++++
 drivers/gpu/drm/i915/display/intel_vga.h     |  4 +++
 drivers/gpu/drm/i915/i915_params.c           |  3 ++
 drivers/gpu/drm/i915/i915_params.h           |  1 +
 6 files changed, 52 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_display.c b/drivers/gpu/drm/i915/display/intel_display.c
index 806d50b302ab..8b07e45c9693 100644
--- a/drivers/gpu/drm/i915/display/intel_display.c
+++ b/drivers/gpu/drm/i915/display/intel_display.c
@@ -9581,9 +9581,11 @@ int intel_modeset_init_noirq(struct drm_i915_private *i915)
 
 	intel_bios_init(i915);
 
-	ret = intel_vga_register(i915);
-	if (ret)
-		goto cleanup_bios;
+	if (!i915_modparams.enable_hd_vgaarb || !HAS_PCH_SPLIT(i915)) {
+		ret = intel_vga_register(i915);
+		if (ret)
+			goto cleanup_bios;
+	}
 
 	/* FIXME: completely on the wrong abstraction layer */
 	intel_power_domains_init_hw(i915, false);
@@ -9734,6 +9736,12 @@ int intel_modeset_init(struct drm_i915_private *i915)
 	if (ret)
 		return ret;
 
+	/*
+	 * Must do this after fbcon init so that
+	 * vgacon_save_screen() works during the handover.
+	 */
+	intel_vga_disable_mem(i915);
+
 	/* Only enable hotplug handling once the fbdev is fully set up. */
 	intel_hpd_init(i915);
 	intel_hpd_poll_disable(i915);
@@ -10467,6 +10475,7 @@ void intel_modeset_driver_remove(struct drm_i915_private *i915)
 	if (!HAS_DISPLAY(i915))
 		return;
 
+	intel_vga_enable_mem(i915);
 	flush_workqueue(i915->flip_wq);
 	flush_workqueue(i915->modeset_wq);
 
diff --git a/drivers/gpu/drm/i915/display/intel_display.h b/drivers/gpu/drm/i915/display/intel_display.h
index 187910d94ec6..82b17d7fee91 100644
--- a/drivers/gpu/drm/i915/display/intel_display.h
+++ b/drivers/gpu/drm/i915/display/intel_display.h
@@ -568,6 +568,7 @@ void i830_disable_pipe(struct drm_i915_private *dev_priv, enum pipe pipe);
 int vlv_get_hpll_vco(struct drm_i915_private *dev_priv);
 int vlv_get_cck_clock(struct drm_i915_private *dev_priv,
 		      const char *name, u32 reg, int ref_freq);
+extern void intel_vga_disable_mem(struct drm_i915_private *dev_priv);
 int vlv_get_cck_clock_hpll(struct drm_i915_private *dev_priv,
 			   const char *name, u32 reg);
 void intel_init_display_hooks(struct drm_i915_private *dev_priv);
diff --git a/drivers/gpu/drm/i915/display/intel_vga.c b/drivers/gpu/drm/i915/display/intel_vga.c
index b5d058404c14..ad23732a9f21 100644
--- a/drivers/gpu/drm/i915/display/intel_vga.c
+++ b/drivers/gpu/drm/i915/display/intel_vga.c
@@ -45,6 +45,36 @@ void intel_vga_disable(struct drm_i915_private *dev_priv)
 	intel_de_posting_read(dev_priv, vga_reg);
 }
 
+void intel_vga_enable_mem(struct drm_i915_private *dev_priv)
+{
+	struct pci_dev *pdev = to_pci_dev(dev_priv->drm.dev);
+
+	/* 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_MIS_R) | (1 << 1), VGA_MIS_W);
+		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 intel_vga_disable_mem(struct drm_i915_private *dev_priv)
+{
+	struct pci_dev *pdev = to_pci_dev(dev_priv->drm.dev);
+	/* 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_MIS_R) & ~(1 << 1), VGA_MIS_W);
+		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_vga_redisable_power_on(struct drm_i915_private *dev_priv)
 {
 	i915_reg_t vga_reg = intel_vga_cntrl_reg(dev_priv);
@@ -53,6 +83,7 @@ void intel_vga_redisable_power_on(struct drm_i915_private *dev_priv)
 		drm_dbg_kms(&dev_priv->drm,
 			    "Something enabled VGA plane, disabling it\n");
 		intel_vga_disable(dev_priv);
+		intel_vga_disable_mem(dev_priv);
 	}
 }
 
diff --git a/drivers/gpu/drm/i915/display/intel_vga.h b/drivers/gpu/drm/i915/display/intel_vga.h
index ba5b55b917f0..7e2af7924e99 100644
--- a/drivers/gpu/drm/i915/display/intel_vga.h
+++ b/drivers/gpu/drm/i915/display/intel_vga.h
@@ -15,4 +15,8 @@ void intel_vga_redisable_power_on(struct drm_i915_private *i915);
 int intel_vga_register(struct drm_i915_private *i915);
 void intel_vga_unregister(struct drm_i915_private *i915);
 
+/* i915 vga arb patch */
+void intel_vga_enable_mem(struct drm_i915_private *i915);
+void intel_vga_disable_mem(struct drm_i915_private *i915);
+
 #endif /* __INTEL_VGA_H__ */
diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
index 701fbc98afa0..4c3701e18a4a 100644
--- a/drivers/gpu/drm/i915/i915_params.c
+++ b/drivers/gpu/drm/i915/i915_params.c
@@ -142,6 +142,9 @@ i915_param_named_unsafe(invert_brightness, int, 0400,
 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(memtest, bool, 0400,
 	"Perform a read/write test of all device memory on module load (default: off)");
 
diff --git a/drivers/gpu/drm/i915/i915_params.h b/drivers/gpu/drm/i915/i915_params.h
index b5e7ea45d191..82d0a75da970 100644
--- a/drivers/gpu/drm/i915/i915_params.h
+++ b/drivers/gpu/drm/i915/i915_params.h
@@ -75,6 +75,7 @@ struct drm_printer;
 	param(unsigned int, request_timeout_ms, CONFIG_DRM_I915_REQUEST_TIMEOUT, CONFIG_DRM_I915_REQUEST_TIMEOUT ? 0600 : 0) \
 	param(unsigned int, lmem_size, 0, 0400) \
 	/* leave bools at the end to not create holes */ \
+	param(bool, enable_hd_vgaarb, false, 0600) \
 	param(bool, enable_hangcheck, true, 0600) \
 	param(bool, load_detect_test, false, 0600) \
 	param(bool, force_reset_modeset_test, false, 0600) \
-- 
2.37.3