[PATCH 4/4] arm64: dts: qcom: x1-dell-thena: bump linux,cma to 256 MiB

[Michael Scott]

The 128 MiB linux,cma reserved-memory pool on dell-thena is too small
to support the camera pipeline in parallel with the normal Linux
desktop. On a freshly-booted system with GNOME running, the typical
runtime consumers — msm DRM framebuffers (Wayland triple buffering on
the eDP panel), qcom_iris video codec buffers, qcom_camss VFE
pre-allocated buffers — already occupy ~100 MiB of the pool, leaving
only ~25 MiB free.

The libcamera "simple" pipeline handler used by /dev/media0 on
dell-thena allocates four ABGR8888 frames at 1920×1088 = 32 MiB total.
That request fails on the fourth frame:

    ERROR DmaBufAllocator: dma-heap allocation failure for frame-3
    ERROR Allocator: Stream is not part of /base/.../camera@10 active configuration
    Can't allocate buffers
    Failed to start camera session

resulting in gnome-snapshot's "Could not play camera stream" and any
other libcamera-mediated app being unable to actually stream.

Bumping linux,cma to 256 MiB (a 0.9% reservation on these laptops'
typical 27 GiB RAM) leaves ~150 MiB free at runtime — sufficient for
the libcamera buffer set plus headroom for video playback or other
CMA-hungry workloads in parallel.

Tested on Dell Latitude 7455: with the 256 MiB pool, CmaFree at
GNOME-desktop idle is ~150 MiB, gnome-snapshot streams the OV02E10
camera cleanly, and `cam -c 1 --capture=2` succeeds.

The companion board files dell-inspiron-14-plus-7441 and the upstream
.dts variants inherit from x1-dell-thena.dtsi, so this changes the
pool size for every dell-thena-based laptop in one place.

Signed-off-by: Michael Scott <mike.scott@xxxxxxxxxxxxxxxx>
---
 arch/arm64/boot/dts/qcom/x1-dell-thena.dtsi | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm64/boot/dts/qcom/x1-dell-thena.dtsi b/arch/arm64/boot/dts/qcom/x1-dell-thena.dtsi
index d93b704872b5..7894d96d34ee 100644
--- a/arch/arm64/boot/dts/qcom/x1-dell-thena.dtsi
+++ b/arch/arm64/boot/dts/qcom/x1-dell-thena.dtsi
@@ -167,7 +167,7 @@ led-camera-indicator {
 	reserved-memory {
 		linux,cma {
 			compatible = "shared-dma-pool";
-			size = <0x0 0x8000000>;
+			size = <0x0 0x10000000>;
 			reusable;
 			linux,cma-default;
 		};
-- 
2.53.0