drm/i915: Add support for LMEM PCIe resizable bar

Add support for the local memory PICe resizable bar, so that
local memory can be resized to the maximum size supported by the device,
and mapped correctly to the PCIe memory bar. It is usual that GPU
devices expose only 256MB BARs primarily to be compatible with 32-bit
systems. So, those devices cannot claim larger memory BAR windows size due
to the system BIOS limitation. With this change, it would be possible to
reprogram the windows of the bridge directly above the requesting device
on the same BAR type.

v2:Moved code to gt/intel_region_lmem.c and used only
single underscore for function names.(Jani)

v3: Optimised code.
Signed-off-by: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Cc: Stuart Summers <stuart.summers@intel.com>
Cc: Michael J Ruhl <michael.j.ruhl@intel.com>
Cc: Prathap Kumar Valsan <prathap.kumar.valsan@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Priyanka Dandamudi <priyanka.dandamudi@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220713130209.2573233-2-priyanka.dandamudi@intel.com

drivers/gpu/drm/i915/gt/intel_region_lmem.c

@@ -15,6 +15,79 @@
 #include "gt/intel_gt_mcr.h"
 #include "gt/intel_gt_regs.h"
 
+static void _release_bars(struct pci_dev *pdev)
+{
+	int resno;
+
+	for (resno = PCI_STD_RESOURCES; resno < PCI_STD_RESOURCE_END; resno++) {
+		if (pci_resource_len(pdev, resno))
+			pci_release_resource(pdev, resno);
+	}
+}
+
+static void
+_resize_bar(struct drm_i915_private *i915, int resno, resource_size_t size)
+{
+	struct pci_dev *pdev = to_pci_dev(i915->drm.dev);
+	int bar_size = pci_rebar_bytes_to_size(size);
+	int ret;
+
+	_release_bars(pdev);
+
+	ret = pci_resize_resource(pdev, resno, bar_size);
+	if (ret) {
+		drm_info(&i915->drm, "Failed to resize BAR%d to %dM (%pe)\n",
+			 resno, 1 << bar_size, ERR_PTR(ret));
+		return;
+	}
+
+	drm_info(&i915->drm, "BAR%d resized to %dM\n", resno, 1 << bar_size);
+}
+
+#define LMEM_BAR_NUM 2
+static void i915_resize_lmem_bar(struct drm_i915_private *i915, resource_size_t lmem_size)
+{
+	struct pci_dev *pdev = to_pci_dev(i915->drm.dev);
+	struct pci_bus *root = pdev->bus;
+	struct resource *root_res;
+	resource_size_t rebar_size;
+	u32 pci_cmd;
+	int i;
+
+	rebar_size = roundup_pow_of_two(pci_resource_len(pdev, LMEM_BAR_NUM));
+
+	if (rebar_size != roundup_pow_of_two(lmem_size))
+		rebar_size = lmem_size;
+	else
+		return;
+
+	/* Find out if root bus contains 64bit memory addressing */
+	while (root->parent)
+		root = root->parent;
+
+	pci_bus_for_each_resource(root, root_res, i) {
+		if (root_res && root_res->flags & (IORESOURCE_MEM | IORESOURCE_MEM_64) &&
+		    root_res->start > 0x100000000ull)
+			break;
+	}
+
+	/* pci_resize_resource will fail anyways */
+	if (!root_res) {
+		drm_info(&i915->drm, "Can't resize LMEM BAR - platform support is missing\n");
+		return;
+	}
+
+	/* First disable PCI memory decoding references */
+	pci_read_config_dword(pdev, PCI_COMMAND, &pci_cmd);
+	pci_write_config_dword(pdev, PCI_COMMAND,
+			       pci_cmd & ~PCI_COMMAND_MEMORY);
+
+	_resize_bar(i915, LMEM_BAR_NUM, rebar_size);
+
+	pci_assign_unassigned_bus_resources(pdev->bus);
+	pci_write_config_dword(pdev, PCI_COMMAND, pci_cmd);
+}
+
 static int
 region_lmem_release(struct intel_memory_region *mem)
 {
@@ -128,6 +201,8 @@ static struct intel_memory_region *setup_lmem(struct intel_gt *gt)
 		lmem_size = intel_uncore_read64(&i915->uncore, GEN12_GSMBASE);
 	}
 
+	i915_resize_lmem_bar(i915, lmem_size);
+
 	if (i915->params.lmem_size > 0) {
 		lmem_size = min_t(resource_size_t, lmem_size,
 				  mul_u32_u32(i915->params.lmem_size, SZ_1M));