[PATCH 1/2] drm/amdgpu: read FB through BAR0 when aperture is unavailable

[chong li <chongli2@amd.com>]

Allow early VRAM reads to fall back to a temporary BAR0 mapping
when the normal aperture mapping has not been established yet.

Signed-off-by: chong li <chongli2@amd.com>
Co-authored-by: Cursor <cursoragent@cursor.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_device.c | 43 +++++++++++++++++++++-
 1 file changed, 42 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
index 5442a1fc1c37..610d82b79de3 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
@@ -743,6 +743,44 @@ void amdgpu_device_mm_access(struct amdgpu_device *adev, loff_t pos,
 	drm_dev_exit(idx);
 }
 
+static int amdgpu_device_read_fb_via_bar0(struct amdgpu_device *adev,
+					  u64 offset, void *buf, size_t size)
+{
+	resource_size_t bar_start, bar_size, map_base;
+	void __iomem *vram;
+	size_t map_offset, map_size;
+	unsigned long flags;
+	u64 end;
+
+	if (!buf || !size)
+		return -EINVAL;
+
+	flags = pci_resource_flags(adev->pdev, 0);
+	if ((flags & IORESOURCE_UNSET) || !(flags & IORESOURCE_MEM))
+		return -EINVAL;
+
+	bar_size = pci_resource_len(adev->pdev, 0);
+	if (!bar_size)
+		return -ENODEV;
+
+	if (check_add_overflow(offset, size, &end) || end > bar_size)
+		return -EINVAL;
+
+	bar_start = pci_resource_start(adev->pdev, 0);
+	map_offset = offset_in_page(offset);
+	map_base = bar_start + (offset & PAGE_MASK);
+	map_size = PAGE_ALIGN(map_offset + size);
+
+	vram = ioremap_wc(map_base, map_size);
+	if (!vram)
+		return -ENOMEM;
+
+	memcpy_fromio(buf, (u8 __iomem *)vram + map_offset, size);
+	iounmap(vram);
+
+	return 0;
+}
+
 /**
  * amdgpu_device_aper_access - access vram by vram aperture
  *
@@ -762,8 +800,11 @@ size_t amdgpu_device_aper_access(struct amdgpu_device *adev, loff_t pos,
 	size_t count = 0;
 	uint64_t last;
 
-	if (!adev->mman.aper_base_kaddr)
+	if (!adev->mman.aper_base_kaddr) {
+		if (!write && !amdgpu_device_read_fb_via_bar0(adev, pos, buf, size))
+			return size;
 		return 0;
+	}
 
 	last = min(pos + size, adev->gmc.visible_vram_size);
 	if (last > pos) {
-- 
2.48.1