[PATCH 3/8] amdgpu: resize BAR0 to the maximum available size, even if it doesn't cover VRAM (v4)

[Darren Salt]

This allows BAR0 resizing to be done for cards which don't advertise support
for a size large enough to cover the VRAM but which do advertise at least
one size larger than the default. For example, my RX 5600 XT, which
advertises 256MB, 512MB and 1GB.

[v4] use bit ops to find sizes to try

[v3] don't use pci_rebar_get_current_size()

[v2] rewritten to use PCI helper functions; some extra log text.

Signed-off-by: Darren Salt <devspam at moreofthesa.me.uk>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 54 ++++++++++++++++++----
 1 file changed, 44 insertions(+), 10 deletions(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index 1595b124c145..b0f8ad603147 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -908,23 +908,29 @@ void amdgpu_device_wb_free(struct amdgpu_device *adev, u32 wb)
  */
 int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
 {
-	u64 space_needed = roundup_pow_of_two(adev->gmc.real_vram_size);
-	u32 rbar_size = order_base_2(((space_needed >> 20) | 1)) - 1;
+	int rbar_size, current_size;
+	u64 current_bytes;
+	u32 available_sizes;
 	struct pci_bus *root;
 	struct resource *res;
 	unsigned i;
 	u16 cmd;
 	int r;
+	bool nospc = false;
 
 	/* Bypass for VF */
 	if (amdgpu_sriov_vf(adev))
 		return 0;
 
-	/* skip if the bios has already enabled large BAR */
-	if (adev->gmc.real_vram_size &&
-	    (pci_resource_len(adev->pdev, 0) >= adev->gmc.real_vram_size))
+	current_bytes = pci_resource_len(adev->pdev, 0);
+
+	/* Skip if the BIOS has already enabled large BAR, covering the VRAM */
+	if (current_bytes >= adev->gmc.real_vram_size)
 		return 0;
 
+	current_size = current_bytes ? pci_rebar_bytes_to_size(current_bytes) : -1;
+	rbar_size = pci_rebar_bytes_to_size(adev->gmc.real_vram_size);
+
 	/* Check if the root BUS has 64bit memory resources */
 	root = adev->pdev->bus;
 	while (root->parent)
@@ -940,6 +946,18 @@ int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
 	if (!res)
 		return 0;
 
+	available_sizes = pci_rebar_get_possible_sizes(adev->pdev, 0);
+	if (available_sizes == 0)
+		return 0;
+
+	/* Find the bit pos representing the smallest size covering the VRAM.
+	 * Otherwise find the bit pos representing the largest available size.
+	 * rbar_size may be smaller but should be unchanged.
+	 */
+	rbar_size = (ffs(available_sizes & (-1 << rbar_size)) ? : fls(available_sizes)) - 1;
+	if (rbar_size < 0)
+		return 0; /* can't happen */
+
 	/* Disable memory decoding while we change the BAR addresses and size */
 	pci_read_config_word(adev->pdev, PCI_COMMAND, &cmd);
 	pci_write_config_word(adev->pdev, PCI_COMMAND,
@@ -952,11 +970,27 @@ int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
 
 	pci_release_resource(adev->pdev, 0);
 
-	r = pci_resize_resource(adev->pdev, 0, rbar_size);
-	if (r == -ENOSPC)
-		DRM_INFO("Not enough PCI address space for a large BAR.");
-	else if (r && r != -ENOTSUPP)
-		DRM_ERROR("Problem resizing BAR0 (%d).", r);
+	for (;
+	     rbar_size >= 0 && rbar_size > current_size;
+	     rbar_size = fls(available_sizes & ~(-1 << rbar_size)) - 1
+	    ) {
+		r = pci_resize_resource(adev->pdev, 0, rbar_size);
+		if (r == 0) {
+			break;
+		} else if (r == -ENOTSUPP) {
+			dev_info(adev->dev, "BAR resizing not supported.");
+			break;
+		} else if (r == -ENOSPC) {
+			if (!nospc) {
+				/* Warn only the first time */
+				dev_info(adev->dev, "Not enough PCI address space for a large BAR.");
+				nospc = true;
+			}
+		} else {
+			dev_err(adev->dev, "Problem resizing BAR0 (%d).", r);
+			break;
+		}
+	}
 
 	pci_assign_unassigned_bus_resources(adev->pdev->bus);
 
-- 
2.20.1