drm/radeon: finish getting bios earlier

Return a number of bytes read in radeon_atrm_get_bios_chunk() and
properly check this value in radeon_atrm_get_bios().
If radeon_atrm_get_bios_chunk() read less bytes then were requested,
it means that it finished reading bios data.

Prior to this patch, condition in radeon_atrm_get_bios() was always
equivalent to "if (ATRM_BIOS_PAGE <= 0)", so it was always false,
thus radeon_atrm_get_bios() was trying to read past the bios data
wasting boot time.

On my lenovo ideapad u455 laptop this patch drops bios reading time
from ~5.5s to ~1.5s.

Signed-off-by: Igor Murzov <e-mail@date.by>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_atpx_handler.c

@@ -60,7 +60,7 @@ static int radeon_atrm_call(acpi_handle atrm_handle, uint8_t *bios,
 	obj = (union acpi_object *)buffer.pointer;
 	memcpy(bios+offset, obj->buffer.pointer, obj->buffer.length);
 	kfree(buffer.pointer);
-	return len;
+	return obj->buffer.length;
 }
 
 bool radeon_atrm_supported(struct pci_dev *pdev)

drivers/gpu/drm/radeon/radeon_bios.c

@@ -120,7 +120,7 @@ static bool radeon_atrm_get_bios(struct radeon_device *rdev)
 		ret = radeon_atrm_get_bios_chunk(rdev->bios,
 						 (i * ATRM_BIOS_PAGE),
 						 ATRM_BIOS_PAGE);
-		if (ret <= 0)
+		if (ret < ATRM_BIOS_PAGE)
 			break;
 	}