drm/linux-core/i915_gem_tiling.c

/*
 * Copyright © 2008 Intel Corporation
 *
 * Permission is hereby granted, free of charge, to any person obtaining a
 * copy of this software and associated documentation files (the "Software"),
 * to deal in the Software without restriction, including without limitation
 * the rights to use, copy, modify, merge, publish, distribute, sublicense,
 * and/or sell copies of the Software, and to permit persons to whom the
 * Software is furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice (including the next
 * paragraph) shall be included in all copies or substantial portions of the
 * Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
 * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
 * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
 * IN THE SOFTWARE.
 *
 * Authors:
 *    Eric Anholt <eric@anholt.net>
 *
 */

#include "drmP.h"
#include "drm.h"
#include "i915_drm.h"
#include "i915_drv.h"

/** @file i915_gem_tiling.c
 *
 * Support for managing tiling state of buffer objects.
 *
 * The idea behind tiling is to increase cache hit rates by rearranging
 * pixel data so that a group of pixel accesses are in the same cacheline.
 * Performance improvement from doing this on the back/depth buffer are on
 * the order of 30%.
 *
 * Intel architectures make this somewhat more complicated, though, by
 * adjustments made to addressing of data when the memory is in interleaved
 * mode (matched pairs of DIMMS) to improve memory bandwidth.
 * For interleaved memory, the CPU sends every sequential 64 bytes
 * to an alternate memory channel so it can get the bandwidth from both.
 *
 * The GPU also rearranges its accesses for increased bandwidth to interleaved
 * memory, and it matches what the CPU does for non-tiled.  However, when tiled
 * it does it a little differently, since one walks addresses not just in the
 * X direction but also Y.  So, along with alternating channels when bit
 * 6 of the address flips, it also alternates when other bits flip --  Bits 9
 * (every 512 bytes, an X tile scanline) and 10 (every two X tile scanlines)
 * are common to both the 915 and 965-class hardware.
 *
 * The CPU also sometimes XORs in higher bits as well, to improve
 * bandwidth doing strided access like we do so frequently in graphics.  This
 * is called "Channel XOR Randomization" in the MCH documentation.  The result
 * is that the CPU is XORing in either bit 11 or bit 17 to bit 6 of its address
 * decode.
 *
 * All of this bit 6 XORing has an effect on our memory management,
 * as we need to make sure that the 3d driver can correctly address object
 * contents.
 *
 * If we don't have interleaved memory, all tiling is safe and no swizzling is
 * required.
 *
 * When bit 17 is XORed in, we simply refuse to tile at all.  Bit
 * 17 is not just a page offset, so as we page an objet out and back in,
 * individual pages in it will have different bit 17 addresses, resulting in
 * each 64 bytes being swapped with its neighbor!
 *
 * Otherwise, if interleaved, we have to tell the 3d driver what the address
 * swizzling it needs to do is, since it's writing with the CPU to the pages
 * (bit 6 and potentially bit 11 XORed in), and the GPU is reading from the
 * pages (bit 6, 9, and 10 XORed in), resulting in a cumulative bit swizzling
 * required by the CPU of XORing in bit 6, 9, 10, and potentially 11, in order
 * to match what the GPU expects.
 */

/**
 * Detects bit 6 swizzling of address lookup between IGD access and CPU
 * access through main memory.
 */
void
i915_gem_detect_bit_6_swizzle(struct drm_device *dev)
{
	drm_i915_private_t *dev_priv = dev->dev_private;
	struct pci_dev *bridge;
	uint32_t swizzle_x = I915_BIT_6_SWIZZLE_UNKNOWN;
	uint32_t swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN;
	int mchbar_offset;
	char __iomem *mchbar;
	int ret;

	bridge = pci_get_bus_and_slot(0, PCI_DEVFN(0, 0));
	if (bridge == NULL) {
		DRM_ERROR("Couldn't get bridge device\n");
		return;
	}

	ret = pci_enable_device(bridge);
	if (ret != 0) {
		DRM_ERROR("pci_enable_device failed: %d\n", ret);
		return;
	}

	if (IS_I965G(dev))
		mchbar_offset = 0x48;
	else
		mchbar_offset = 0x44;

	/* Use resource 2 for our BAR that's stashed in a nonstandard location,
	 * since the bridge would only ever use standard BARs 0-1 (though it
	 * doesn't anyway)
	 */
	ret = pci_read_base(bridge, mchbar_offset, &bridge->resource[2]);
	if (ret != 0) {
		DRM_ERROR("pci_read_base failed: %d\n", ret);
		return;
	}

	mchbar = ioremap(pci_resource_start(bridge, 2),
			 pci_resource_len(bridge, 2));
	if (mchbar == NULL) {
		DRM_ERROR("Couldn't map MCHBAR to determine tile swizzling\n");
		return;
	}

	if (IS_I965G(dev) && !IS_I965GM(dev)) {
		uint32_t chdecmisc;

		/* On the 965, channel interleave appears to be determined by
		 * the flex bit.  If flex is set, then the ranks (sides of a
		 * DIMM) of memory will be "stacked" (physical addresses walk
		 * through one rank then move on to the next, flipping channels
		 * or not depending on rank configuration).  The GPU in this
		 * case does exactly the same addressing as the CPU.
		 *
		 * Unlike the 945, channel randomization based does not
		 * appear to be available.
		 *
		 * XXX: While the G965 doesn't appear to do any interleaving
		 * when the DIMMs are not exactly matched, the G4x chipsets
		 * might be for "L-shaped" configurations, and will need to be
		 * detected.
		 *
		 * L-shaped configuration:
		 *
		 * +-----+
		 * |     |
		 * |DIMM2|         <-- non-interleaved
		 * +-----+
		 * +-----+ +-----+
		 * |     | |     |
		 * |DIMM0| |DIMM1| <-- interleaved area
		 * +-----+ +-----+
		 */
		chdecmisc = readb(mchbar + CHDECMISC);

		if (chdecmisc == 0xff) {
			DRM_ERROR("Couldn't read from MCHBAR.  "
				  "Disabling tiling.\n");
		} else if (chdecmisc & CHDECMISC_FLEXMEMORY) {
			swizzle_x = I915_BIT_6_SWIZZLE_NONE;
			swizzle_y = I915_BIT_6_SWIZZLE_NONE;
		} else {
			swizzle_x = I915_BIT_6_SWIZZLE_9_10;
			swizzle_y = I915_BIT_6_SWIZZLE_9;
		}
	} else if (IS_I9XX(dev)) {
		uint32_t dcc;

		/* 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
		 * on bit 6, 9, and 10 for X, but the CPU may also optionally
		 * alternate based on bit 17 (XOR not disabled and XOR
		 * bit == 17).
		 */
		dcc = readl(mchbar + DCC);
		switch (dcc & DCC_ADDRESSING_MODE_MASK) {
		case DCC_ADDRESSING_MODE_SINGLE_CHANNEL:
		case DCC_ADDRESSING_MODE_DUAL_CHANNEL_ASYMMETRIC:
			swizzle_x = I915_BIT_6_SWIZZLE_NONE;
			swizzle_y = I915_BIT_6_SWIZZLE_NONE;
			break;
		case DCC_ADDRESSING_MODE_DUAL_CHANNEL_INTERLEAVED:
			if (IS_I915G(dev) || IS_I915GM(dev) ||
			    dcc & DCC_CHANNEL_XOR_DISABLE) {
				swizzle_x = I915_BIT_6_SWIZZLE_9_10;
				swizzle_y = I915_BIT_6_SWIZZLE_9;
			} else if (IS_I965GM(dev)) {
				/* GM965 only does bit 11-based channel
				 * randomization
				 */
				swizzle_x = I915_BIT_6_SWIZZLE_9_10_11;
				swizzle_y = I915_BIT_6_SWIZZLE_9_11;
			} else {
				/* Bit 17 or perhaps other swizzling */
				swizzle_x = I915_BIT_6_SWIZZLE_UNKNOWN;
				swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN;
			}
			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;
		}
	} else {
		/* As far as we know, the 865 doesn't have these bit 6
		 * swizzling issues.
		 */
		swizzle_x = I915_BIT_6_SWIZZLE_NONE;
		swizzle_y = I915_BIT_6_SWIZZLE_NONE;
	}

	iounmap(mchbar);

	dev_priv->mm.bit_6_swizzle_x = swizzle_x;
	dev_priv->mm.bit_6_swizzle_y = swizzle_y;
}

/**
 * Sets the tiling mode of an object, returning the required swizzling of
 * bit 6 of addresses in the object.
 */
int
i915_gem_set_tiling(struct drm_device *dev, void *data,
		   struct drm_file *file_priv)
{
	struct drm_i915_gem_set_tiling *args = data;
	drm_i915_private_t *dev_priv = dev->dev_private;
	struct drm_gem_object *obj;
	struct drm_i915_gem_object *obj_priv;

	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
	if (obj == NULL)
		return -EINVAL;
	obj_priv = obj->driver_private;

	mutex_lock(&dev->struct_mutex);

	if (args->tiling_mode == I915_TILING_NONE) {
		obj_priv->tiling_mode = I915_TILING_NONE;
		args->swizzle_mode = I915_BIT_6_SWIZZLE_NONE;
	} else {
		if (args->tiling_mode == I915_TILING_X)
			args->swizzle_mode = dev_priv->mm.bit_6_swizzle_x;
		else
			args->swizzle_mode = dev_priv->mm.bit_6_swizzle_y;
		/* If we can't handle the swizzling, make it untiled. */
		if (args->swizzle_mode == I915_BIT_6_SWIZZLE_UNKNOWN) {
			args->tiling_mode = I915_TILING_NONE;
			args->swizzle_mode = I915_BIT_6_SWIZZLE_NONE;
		}
	}
	obj_priv->tiling_mode = args->tiling_mode;

	mutex_unlock(&dev->struct_mutex);

	drm_gem_object_unreference(obj);

	return 0;
}

/**
 * Returns the current tiling mode and required bit 6 swizzling for the object.
 */
int
i915_gem_get_tiling(struct drm_device *dev, void *data,
		   struct drm_file *file_priv)
{
	struct drm_i915_gem_get_tiling *args = data;
	drm_i915_private_t *dev_priv = dev->dev_private;
	struct drm_gem_object *obj;
	struct drm_i915_gem_object *obj_priv;

	obj = drm_gem_object_lookup(dev, file_priv, args->handle);
	if (obj == NULL)
		return -EINVAL;
	obj_priv = obj->driver_private;

	mutex_lock(&dev->struct_mutex);

	args->tiling_mode = obj_priv->tiling_mode;
	switch (obj_priv->tiling_mode) {
	case I915_TILING_X:
		args->swizzle_mode = dev_priv->mm.bit_6_swizzle_x;
		break;
	case I915_TILING_Y:
		args->swizzle_mode = dev_priv->mm.bit_6_swizzle_y;
		break;
	case I915_TILING_NONE:
		args->swizzle_mode = I915_BIT_6_SWIZZLE_NONE;
		break;
	default:
		DRM_ERROR("unknown tiling mode\n");
	}

	mutex_unlock(&dev->struct_mutex);

	drm_gem_object_unreference(obj);

	return 0;
}