drm/xe: Simplify rebar sizing

"Right sizing" the PCI BAR is not necessary.  If rebar is needed
size to the maximum available.

Preserve the force_vram_bar_size sizing.
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/xe/xe_device_types.h

 /* SPDX-License-Identifier: MIT */
 /*
- * Copyright © 2022 Intel Corporation
+ * Copyright © 2022-2023 Intel Corporation
  */
 
 #ifndef _XE_DEVICE_TYPES_H_
@@ -133,11 +133,13 @@ struct xe_device {
 			/**
 			 * @io_size: IO size of VRAM.
 			 *
-			 * This represents how much of VRAM we can access via
-			 * the CPU through the VRAM BAR. This can be smaller
-			 * than @size, in which case only part of VRAM is CPU
-			 * accessible (typically the first 256M). This
-			 * configuration is known as small-bar.
+			 * This represents how much of VRAM the CPU can access
+			 * via the VRAM BAR.
+			 * On systems that do not support large BAR IO space,
+			 * this can be smaller than the actual memory size, in
+			 * which case only part of VRAM is CPU accessible
+			 * (typically the first 256M).  This configuration is
+			 * known as small-bar.
 			 */
 			resource_size_t io_size;
 			/** @size: Total size of VRAM */

drivers/gpu/drm/xe/xe_gt_types.h

 /* SPDX-License-Identifier: MIT */
 /*
- * Copyright © 2022 Intel Corporation
+ * Copyright © 2022-2023 Intel Corporation
  */
 
 #ifndef _XE_GT_TYPES_H_
@@ -148,11 +148,11 @@ struct xe_gt {
 			/**
 			 * @io_size: IO size of this VRAM instance
 			 *
-			 * This represents how much of this VRAM we can access
-			 * via the CPU through the VRAM BAR. This can be smaller
-			 * than @size, in which case only part of VRAM is CPU
-			 * accessible (typically the first 256M). This
-			 * configuration is known as small-bar.
+			 * This represents how much of the VRAM the CPU can access
+			 * via the VRAM BAR.
+			 * This can be smaller than the actual @size, in which
+			 * case only part of VRAM is CPU accessible (typically
+			 * the first 256M). This configuration is known as small-bar.
 			 */
 			resource_size_t io_size;
 			/** @size: size of VRAM. */

drivers/gpu/drm/xe/xe_mmio.c

@@ -3,6 +3,8 @@
  * Copyright © 2021-2023 Intel Corporation
  */
 
+#include <linux/minmax.h>
+
 #include "xe_mmio.h"
 
 #include <drm/drm_managed.h>
@@ -21,6 +23,8 @@
 #define XEHP_MTCFG_ADDR		XE_REG(0x101800)
 #define TILE_COUNT		REG_GENMASK(15, 8)
 
+#define BAR_SIZE_SHIFT 20
+
 static int xe_set_dma_info(struct xe_device *xe)
 {
 	unsigned int mask_size = xe->info.dma_mask_size;
@@ -57,49 +61,61 @@ _resize_bar(struct xe_device *xe, int resno, resource_size_t size)
 	if (ret) {
 		drm_info(&xe->drm, "Failed to resize BAR%d to %dM (%pe). Consider enabling 'Resizable BAR' support in your BIOS\n",
 			 resno, 1 << bar_size, ERR_PTR(ret));
-		return -1;
+		return ret;
 	}
 
 	drm_info(&xe->drm, "BAR%d resized to %dM\n", resno, 1 << bar_size);
-	return 1;
+	return ret;
 }
 
-static int xe_resize_vram_bar(struct xe_device *xe, resource_size_t vram_size)
+/*
+ * if force_vram_bar_size is set, attempt to set to the requested size
+ * else set to maximum possible size
+ */
+static int xe_resize_vram_bar(struct xe_device *xe)
 {
+	u64 force_vram_bar_size = xe_force_vram_bar_size;
 	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
 	struct pci_bus *root = pdev->bus;
-	struct resource *root_res;
-	resource_size_t rebar_size;
 	resource_size_t current_size;
+	resource_size_t rebar_size;
+	struct resource *root_res;
+	u32 bar_size_mask;
 	u32 pci_cmd;
 	int i;
 	int ret;
-	u64 force_vram_bar_size = xe_force_vram_bar_size;
 
-	current_size = roundup_pow_of_two(pci_resource_len(pdev, GEN12_LMEM_BAR));
+	/* gather some relevant info */
+	current_size = pci_resource_len(pdev, GEN12_LMEM_BAR);
+	bar_size_mask = pci_rebar_get_possible_sizes(pdev, GEN12_LMEM_BAR);
 
+	if (!bar_size_mask)
+		return 0;
+
+	/* set to a specific size? */
 	if (force_vram_bar_size) {
-		u32 bar_sizes;
+		u32 bar_size_bit;
 
 		rebar_size = force_vram_bar_size * (resource_size_t)SZ_1M;
-		bar_sizes = pci_rebar_get_possible_sizes(pdev, GEN12_LMEM_BAR);
 
-		if (rebar_size == current_size)
-			return 0;
+		bar_size_bit = bar_size_mask & BIT(pci_rebar_bytes_to_size(rebar_size));
 
-		if (!(bar_sizes & BIT(pci_rebar_bytes_to_size(rebar_size))) ||
-		    rebar_size >= roundup_pow_of_two(vram_size)) {
-			rebar_size = vram_size;
+		if (!bar_size_bit) {
 			drm_info(&xe->drm,
-				 "Given bar size is not within supported size, setting it to default: %lluMiB\n",
-				 (u64)vram_size >> 20);
+				 "Requested size: %lluMiB is not supported by rebar sizes: 0x%x. Leaving default: %lluMiB\n",
+				 (u64)rebar_size >> 20, bar_size_mask, (u64)current_size >> 20);
+			return 0;
 		}
+
+		rebar_size = 1ULL << (__fls(bar_size_bit) + BAR_SIZE_SHIFT);
+
+		if (rebar_size == current_size)
+			return 0;
 	} else {
-		rebar_size = current_size;
+		rebar_size = 1ULL << (__fls(bar_size_mask) + BAR_SIZE_SHIFT);
 
-		if (rebar_size != roundup_pow_of_two(vram_size))
-			rebar_size = vram_size;
-		else
+		/* only resize if larger than current */
+		if (rebar_size <= current_size)
 			return 0;
 	}
 
@@ -144,6 +160,31 @@ static bool xe_pci_resource_valid(struct pci_dev *pdev, int bar)
 	return true;
 }
 
+static int xe_determine_lmem_bar_size(struct xe_device *xe)
+{
+	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
+	int err;
+
+	if (!xe_pci_resource_valid(pdev, GEN12_LMEM_BAR)) {
+		drm_err(&xe->drm, "pci resource is not valid\n");
+		return -ENXIO;
+	}
+
+	err = xe_resize_vram_bar(xe);
+	if (err)
+		return err;
+
+	xe->mem.vram.io_start = pci_resource_start(pdev, GEN12_LMEM_BAR);
+	xe->mem.vram.io_size = pci_resource_len(pdev, GEN12_LMEM_BAR);
+	if (!xe->mem.vram.io_size)
+		return -EIO;
+
+	/* set up a map to the total memory area. */
+	xe->mem.vram.mapping = ioremap_wc(xe->mem.vram.io_start, xe->mem.vram.io_size);
+
+	return 0;
+}
+
 /**
  * xe_mmio_tile_vram_size() - Collect vram size and offset information
  * @gt: tile to get info for
@@ -199,59 +240,37 @@ int xe_mmio_tile_vram_size(struct xe_gt *gt, u64 *vram_size, u64 *tile_size, u64
 
 int xe_mmio_probe_vram(struct xe_device *xe)
 {
-	struct pci_dev *pdev = to_pci_dev(xe->drm.dev);
 	struct xe_gt *gt;
-	u64 original_size;
 	u64 tile_offset;
 	u64 tile_size;
 	u64 vram_size;
 	int err;
 	u8 id;
 
-	if (!IS_DGFX(xe)) {
-		xe->mem.vram.mapping = 0;
-		xe->mem.vram.size = 0;
-		xe->mem.vram.io_start = 0;
-		xe->mem.vram.io_size = 0;
-
-		for_each_gt(gt, xe, id) {
-			gt->mem.vram.mapping = 0;
-			gt->mem.vram.size = 0;
-			gt->mem.vram.io_start = 0;
-			gt->mem.vram.io_size = 0;
-		}
+	if (!IS_DGFX(xe))
 		return 0;
-	}
-
-	if (!xe_pci_resource_valid(pdev, GEN12_LMEM_BAR)) {
-		drm_err(&xe->drm, "pci resource is not valid\n");
-		return -ENXIO;
-	}
 
+	/* Get the size of the gt0 vram for later accessibility comparison */
 	gt = xe_device_get_gt(xe, 0);
-	original_size = pci_resource_len(pdev, GEN12_LMEM_BAR);
-
 	err = xe_mmio_tile_vram_size(gt, &vram_size, &tile_size, &tile_offset);
 	if (err)
 		return err;
 
-	xe_resize_vram_bar(xe, vram_size);
-	xe->mem.vram.io_start = pci_resource_start(pdev, GEN12_LMEM_BAR);
-	xe->mem.vram.io_size = min(vram_size,
-				   pci_resource_len(pdev, GEN12_LMEM_BAR));
-	xe->mem.vram.size = xe->mem.vram.io_size;
-
-	if (!xe->mem.vram.size)
-		return -EIO;
+	err = xe_determine_lmem_bar_size(xe);
+	if (err)
+		return err;
 
-	if (vram_size > xe->mem.vram.io_size)
-		drm_warn(&xe->drm, "Restricting VRAM size to PCI resource size (%lluMiB->%lluMiB)\n",
-			 (u64)vram_size >> 20, (u64)xe->mem.vram.io_size >> 20);
+	/* small bar issues will only cover gt0 sizes */
+	if (xe->mem.vram.io_size < vram_size)
+		drm_warn(&xe->drm, "Restricting VRAM size to PCI resource size (0x%llx->0x%llx)\n",
+			 vram_size, (u64)xe->mem.vram.io_size);
 
-	xe->mem.vram.mapping = ioremap_wc(xe->mem.vram.io_start, xe->mem.vram.io_size);
-	xe->mem.vram.size = min_t(u64, xe->mem.vram.size, vram_size);
+	/* Limit size to available memory to account for the current memory algorithm */
+	xe->mem.vram.io_size = min_t(u64, xe->mem.vram.io_size, vram_size);
+	xe->mem.vram.size = xe->mem.vram.io_size;
 
-	drm_info(&xe->drm, "TOTAL VRAM: %pa, %pa\n", &xe->mem.vram.io_start, &xe->mem.vram.size);
+	drm_info(&xe->drm, "VISIBLE VRAM: %pa, %pa\n", &xe->mem.vram.io_start,
+		 &xe->mem.vram.io_size);
 
 	/* FIXME: Assuming equally partitioned VRAM, incorrect */
 	if (xe->info.tile_count > 1) {