drm/amdgpu: Resize BAR0 to the maximum available size, even if it doesn't cover VRAM

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.
Signed-off-by: Darren Salt <devspam@moreofthesa.me.uk>
Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Nirmoy Das <nirmoy.das@amd.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20210107175017.15893-4-nirmoy.das@amd.com

drivers/gpu/drm/amd/amdgpu/amdgpu_device.c

@@ -1107,7 +1107,7 @@ 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 = pci_rebar_bytes_to_size(adev->gmc.real_vram_size);
 	struct pci_bus *root;
 	struct resource *res;
 	unsigned i;
@@ -1138,6 +1138,10 @@ int amdgpu_device_resize_fb_bar(struct amdgpu_device *adev)
 	if (!res)
 		return 0;
 
+	/* Limit the BAR size to what is available */
+	rbar_size = min(fls(pci_rebar_get_possible_sizes(adev->pdev, 0)) - 1,
+			rbar_size);
+
 	/* 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,