[RFC PATCH 1/2] drm/ttm: save the device's DMA coherency status in ttm_device

[Icenowy Zheng <uwu@icenowy.me>]

Currently TTM utilizes cached memory regardless of whether the device
have full DMA coherency (can snoop CPU cache).

Save the device's DMA coherency status in struct ttm_device, to allow
further support of devices w/o snooping capability (the capability
missing on at least one part of the transmission between the CPU and the
device).

Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
---
 drivers/gpu/drm/ttm/ttm_device.c | 2 ++
 include/drm/ttm/ttm_device.h     | 5 +++++
 2 files changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/ttm/ttm_device.c b/drivers/gpu/drm/ttm/ttm_device.c
index 434cf0258000e..b923c14861c1a 100644
--- a/drivers/gpu/drm/ttm/ttm_device.c
+++ b/drivers/gpu/drm/ttm/ttm_device.c
@@ -237,6 +237,8 @@ int ttm_device_init(struct ttm_device *bdev, const struct ttm_device_funcs *func
 	list_add_tail(&bdev->device_list, &glob->device_list);
 	mutex_unlock(&ttm_global_mutex);
 
+	bdev->dma_coherent = dev->dma_coherent;
+
 	return 0;
 }
 EXPORT_SYMBOL(ttm_device_init);
diff --git a/include/drm/ttm/ttm_device.h b/include/drm/ttm/ttm_device.h
index c22f30535c848..9daf7f47d6507 100644
--- a/include/drm/ttm/ttm_device.h
+++ b/include/drm/ttm/ttm_device.h
@@ -225,6 +225,11 @@ struct ttm_device {
 	 */
 	const struct ttm_device_funcs *funcs;
 
+	/**
+	 * @dma_coherent: if the device backed is dma-coherent.
+	 */
+	bool dma_coherent;
+
 	/**
 	 * @sysman: Resource manager for the system domain.
 	 * Access via ttm_manager_type.
-- 
2.45.2