linux/drivers/gpu/drm/i915/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;
	uint32_t swizzle_x = I915_BIT_6_SWIZZLE_UNKNOWN;
	uint32_t swizzle_y = I915_BIT_6_SWIZZLE_UNKNOWN;

	if (!IS_I9XX(dev)) {
		/* 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;
	} else if (IS_MOBILE(dev)) {
		uint32_t dcc;

		/* On mobile 9xx chipsets, channel interleave by the CPU is
		 * determined by DCC.  For single-channel, neither the CPU
		 * nor the GPU do swizzling.  For dual channel interleaved,
		 * the GPU's interleave is bit 9 and 10 for X tiled, and bit
		 * 9 for Y tiled.  The CPU's interleave is independent, and
		 * can be based on either bit 11 (haven't seen this yet) or
		 * bit 17 (common).
		 */
		dcc = I915_READ(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 (dcc & DCC_CHANNEL_XOR_DISABLE) {
				/* This is the base swizzling by the GPU for
				 * tiled buffers.
				 */
				swizzle_x = I915_BIT_6_SWIZZLE_9_10;
				swizzle_y = I915_BIT_6_SWIZZLE_9;
			} else if ((dcc & DCC_CHANNEL_XOR_BIT_17) == 0) {
				/* Bit 11 swizzling by the CPU in addition. */
				swizzle_x = I915_BIT_6_SWIZZLE_9_10_11;
				swizzle_y = I915_BIT_6_SWIZZLE_9_11;
			} else {
				/* Bit 17 swizzling by the CPU in addition. */
				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 {
		/* The 965, G33, and newer, have a very flexible memory
		 * configuration.  It will enable dual-channel mode
		 * (interleaving) on as much memory as it can, and the GPU
		 * will additionally sometimes enable different bit 6
		 * swizzling for tiled objects from the CPU.
		 *
		 * Here's what I found on the G965:
		 *    slot fill         memory size  swizzling
		 * 0A   0B   1A   1B    1-ch   2-ch
		 * 512  0    0    0     512    0     O
		 * 512  0    512  0     16     1008  X
		 * 512  0    0    512   16     1008  X
		 * 0    512  0    512   16     1008  X
		 * 1024 1024 1024 0     2048   1024  O
		 *
		 * We could probably detect this based on either the DRB
		 * matching, which was the case for the swizzling required in
		 * the table above, or from the 1-ch value being less than
		 * the minimum size of a rank.
		 */
		if (I915_READ16(C0DRB3) != I915_READ16(C1DRB3)) {
			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;
		}
	}

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


/**
 * Returns the size of the fence for a tiled object of the given size.
 */
static int
i915_get_fence_size(struct drm_device *dev, int size)
{
	int i;
	int start;

	if (IS_I965G(dev)) {
		/* The 965 can have fences at any page boundary. */
		return ALIGN(size, 4096);
	} else {
		/* Align the size to a power of two greater than the smallest
		 * fence size.
		 */
		if (IS_I9XX(dev))
			start = 1024 * 1024;
		else
			start = 512 * 1024;

		for (i = start; i < size; i <<= 1)
			;

		return i;
	}
}

/* Check pitch constriants for all chips & tiling formats */
static bool
i915_tiling_ok(struct drm_device *dev, int stride, int size, int tiling_mode)
{
	int tile_width;

	/* Linear is always fine */
	if (tiling_mode == I915_TILING_NONE)
		return true;

	if (tiling_mode == I915_TILING_Y && HAS_128_BYTE_Y_TILING(dev))
		tile_width = 128;
	else
		tile_width = 512;

	/* 965+ just needs multiples of tile width */
	if (IS_I965G(dev)) {
		if (stride & (tile_width - 1))
			return false;
		return true;
	}

	/* Pre-965 needs power of two tile widths */
	if (stride < tile_width)
		return false;

	if (stride & (stride - 1))
		return false;

	/* We don't handle the aperture area covered by the fence being bigger
	 * than the object size.
	 */
	if (i915_get_fence_size(dev, size) != size)
		return false;

	return true;
}

/**
 * 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;

	if (!i915_tiling_ok(dev, args->stride, obj->size, args->tiling_mode)) {
		drm_gem_object_unreference(obj);
		return -EINVAL;
	}

	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;
		}
	}
	if (args->tiling_mode != obj_priv->tiling_mode) {
		int ret;

		/* Unbind the object, as switching tiling means we're
		 * switching the cache organization due to fencing, probably.
		 */
		ret = i915_gem_object_unbind(obj);
		if (ret != 0) {
			WARN(ret != -ERESTARTSYS,
			     "failed to unbind object for tiling switch");
			args->tiling_mode = obj_priv->tiling_mode;
			mutex_unlock(&dev->struct_mutex);
			drm_gem_object_unreference(obj);

			return ret;
		}
		obj_priv->tiling_mode = args->tiling_mode;
	}
	obj_priv->stride = args->stride;

	drm_gem_object_unreference(obj);
	mutex_unlock(&dev->struct_mutex);

	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");
	}

	drm_gem_object_unreference(obj);
	mutex_unlock(&dev->struct_mutex);

	return 0;
}