[Intel-gfx] [PATCH] allocate & enable MCHBAR if needed

[Jesse Barnes]

I noticed on my Eee 901 that the i915 DRM driver wasn't reading the MCHBAR reg
at startup time, and so it would disable tiling.  For decent performance,
especially on an Eee-like platform, tiling is a must.  So I put this patch
together to allocate MCHBAR space and enable it if necessary.

In combination with the pre-965 tiling patches in the tree now, you should see
a big performance improvement if you have an affected machine.

(Note to Eric: don't merge this until someone else confirms it works for them
too.)

Signed-off-by: Jesse Barnes <jbarnes at virtuousgeek.org>

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 72b9314..a8d3256 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -143,6 +143,8 @@ typedef struct drm_i915_private {
 	drm_local_map_t hws_map;
 	struct drm_gem_object *hws_obj;
 
+	struct resource mch_res;
+
 	unsigned int cpp;
 	int back_offset;
 	int front_offset;
diff --git a/drivers/gpu/drm/i915/i915_gem_tiling.c b/drivers/gpu/drm/i915/i915_gem_tiling.c
index 7fb4191..06250dc 100644
--- a/drivers/gpu/drm/i915/i915_gem_tiling.c
+++ b/drivers/gpu/drm/i915/i915_gem_tiling.c
@@ -24,6 +24,7 @@
  *    Eric Anholt <eric at anholt.net>
  *
  */
+#include <linux/acpi.h>
 
 #include "drmP.h"
 #include "drm.h"
@@ -79,6 +80,136 @@
  * to match what the GPU expects.
  */
 
+#define MCHBAR_I915 0x44
+#define MCHBAR_I965 0x48
+#define MCHBAR_SIZE (4*4096)
+
+#define DEVEN_REG 0x54
+#define   DEVEN_MCHBAR_EN (1 << 28)
+
+/* Allocate space for the MCH regs if needed, return nonzero on error */
+static int
+intel_alloc_mchbar_resource(struct drm_device *dev)
+{
+	struct pci_dev *bridge_dev;
+	drm_i915_private_t *dev_priv = dev->dev_private;
+	int reg = IS_I965G(dev) ? MCHBAR_I965 : MCHBAR_I915;
+	u32 temp_lo, temp_hi = 0;
+	u64 mchbar_addr;
+	int ret = 0;
+
+	bridge_dev = pci_get_bus_and_slot(0, PCI_DEVFN(0,0));
+	if (!bridge_dev) {
+		DRM_DEBUG("no bridge dev?!\n");
+		ret = -ENODEV;
+		goto out;
+	}
+
+	if (IS_I965G(dev))
+		pci_read_config_dword(bridge_dev, reg + 4, &temp_hi);
+	pci_read_config_dword(bridge_dev, reg, &temp_lo);
+	mchbar_addr = ((u64)temp_hi << 32) | temp_lo;
+
+	/* Get some space for it */
+	ret = pci_bus_alloc_resource(bridge_dev->bus, &dev_priv->mch_res,
+				     MCHBAR_SIZE, MCHBAR_SIZE,
+				     PCIBIOS_MIN_MEM,
+				     0,   pcibios_align_resource,
+				     bridge_dev);
+	if (ret) {
+		DRM_DEBUG("failed bus alloc: %d\n", ret);
+		dev_priv->mch_res.start = 0;
+		goto out_put;
+	}
+
+	if (IS_I965G(dev))
+		pci_write_config_dword(bridge_dev, reg + 4,
+				       upper_32_bits(dev_priv->mch_res.start));
+
+	pci_write_config_dword(bridge_dev, reg,
+			       lower_32_bits(dev_priv->mch_res.start));
+out_put:
+	pci_dev_put(bridge_dev);
+out:
+	return ret;
+}
+
+/* Setup MCHBAR if possible, return true if we should disable it again */
+static bool
+intel_setup_mchbar(struct drm_device *dev)
+{
+	struct pci_dev *bridge_dev;
+	int mchbar_reg = IS_I965G(dev) ? MCHBAR_I965 : MCHBAR_I915;
+	u32 temp;
+	bool need_disable = false, enabled;
+
+	bridge_dev = pci_get_bus_and_slot(0, PCI_DEVFN(0,0));
+	if (!bridge_dev) {
+		DRM_DEBUG("no bridge dev?!\n");
+		goto out;
+	}
+
+	if (IS_I915G(dev) || IS_I915GM(dev)) {
+		pci_read_config_dword(bridge_dev, DEVEN_REG, &temp);
+		enabled = !!(temp & DEVEN_MCHBAR_EN);
+	} else {
+		pci_read_config_dword(bridge_dev, mchbar_reg, &temp);
+		enabled = temp & 1;
+	}
+
+	/* If it's already enabled, don't have to do anything */
+	if (enabled)
+		goto out_put;
+
+	if (intel_alloc_mchbar_resource(dev))
+		goto out_put;
+
+	need_disable = true;
+
+	if (IS_I915G(dev) || IS_I915GM(dev))
+		pci_write_config_dword(bridge_dev, DEVEN_REG,
+				       temp | DEVEN_MCHBAR_EN);
+	else
+		pci_write_config_dword(bridge_dev, mchbar_reg, temp | 1);
+
+out_put:
+	pci_dev_put(bridge_dev);
+out:
+	return need_disable;
+}
+
+static void
+intel_teardown_mchbar(struct drm_device *dev, bool disable)
+{
+	drm_i915_private_t *dev_priv = dev->dev_private;
+	struct pci_dev *bridge_dev;
+	int mchbar_reg = IS_I965G(dev) ? MCHBAR_I965 : MCHBAR_I915;
+	u32 temp;
+
+	bridge_dev = pci_get_bus_and_slot(0, PCI_DEVFN(0,0));
+	if (!bridge_dev) {
+		DRM_DEBUG("no bridge dev?!\n");
+		return;
+	}
+
+	if (disable) {
+		if (IS_I915G(dev) || IS_I915GM(dev)) {
+			pci_read_config_dword(bridge_dev, DEVEN_REG, &temp);
+			temp &= ~DEVEN_MCHBAR_EN;
+			pci_write_config_dword(bridge_dev, DEVEN_REG, temp);
+		} else {
+			pci_read_config_dword(bridge_dev, mchbar_reg, &temp);
+			temp &= ~1;
+			pci_write_config_dword(bridge_dev, mchbar_reg, temp);
+		}
+	}
+
+	if (dev_priv->mch_res.start)
+		release_resource(&dev_priv->mch_res);
+
+	pci_dev_put(bridge_dev);
+}
+
 /**
  * Detects bit 6 swizzling of address lookup between IGD access and CPU
  * access through main memory.
@@ -89,6 +220,7 @@ i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
 	drm_i915_private_t *dev_priv = dev->dev_private;
 	uint32_t swizzle_x = I915_BIT_6_SWIZZLE_UNKNOWN;
 	uint32_t swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN;
+	bool need_disable;
 
 	if (!IS_I9XX(dev)) {
 		/* As far as we know, the 865 doesn't have these bit 6
@@ -100,6 +232,9 @@ i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
 		   IS_GM45(dev)) {
 		uint32_t dcc;
 
+		/* Try to make sure MCHBAR is enabled before poking at it */
+		need_disable = intel_setup_mchbar(dev);
+
 		/* On 915-945 and GM965, channel interleave by the CPU is
 		 * determined by DCC.  The CPU will alternate based on bit 6
 		 * in interleaved mode, and the GPU will then also alternate
@@ -134,11 +269,11 @@ i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
 			break;
 		}
 		if (dcc == 0xffffffff) {
-			DRM_ERROR("Couldn't read from MCHBAR.  "
-				  "Disabling tiling.\n");
 			swizzle_x = I915_BIT_6_SWIZZLE_UNKNOWN;
 			swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN;
 		}
+
+		intel_teardown_mchbar(dev, need_disable);
 	} else {
 		/* The 965, G33, and newer, have a very flexible memory
 		 * configuration.  It will enable dual-channel mode