dmaengine: nbpfaxi: add optional max-burst property for memory reads/writes

Due to a hardware bug, reading memory (from the Accelerator Coherency Port)
with a burst size equal to the maximum burst size allowed by the DMA
hardware's buffer size will cause a hardware hang on the ARTPEC-6 SoC,
where the only solution is a manual power cycle.
On ARTPEC-6, this hardware bug does not trigger when writing memory (to the
Accelerator Coherency Port) with a burst size equal to the maximum burst
size allowed by the DMA hardware's buffer size.

To avoid this hardware hang, introduce a new optional max-burst property
for memory reads. For completeness, also introduce a max-burst property for
memory writes.

Signed-off-by: Niklas Cassel <niklas.cassel@axis.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/Documentation/devicetree/bindings/dma/nbpfaxi.txt b/Documentation/devicetree/bindings/dma/nbpfaxi.txt
index d5e2522b9ec1..d2e1e62e346a 100644
--- a/Documentation/devicetree/bindings/dma/nbpfaxi.txt
+++ b/Documentation/devicetree/bindings/dma/nbpfaxi.txt
@@ -23,6 +23,14 @@ Required properties
 #define NBPF_SLAVE_RQ_LEVEL	4
 
 Optional properties:
+- max-burst-mem-read:	limit burst size for memory reads
+  (DMA_MEM_TO_MEM/DMA_MEM_TO_DEV) to this value, specified in bytes, rather
+  than using the maximum burst size allowed by the hardware's buffer size.
+- max-burst-mem-write:	limit burst size for memory writes
+  (DMA_DEV_TO_MEM/DMA_MEM_TO_MEM) to this value, specified in bytes, rather
+  than using the maximum burst size allowed by the hardware's buffer size.
+  If both max-burst-mem-read and max-burst-mem-write are set, DMA_MEM_TO_MEM
+  will use the lower value.
 
 You can use dma-channels and dma-requests as described in dma.txt, although they
 won't be used, this information is derived from the compatibility string.