[PATCH v2 1/4] dt-bindings: Document the STM32 DMA bindings

Mark Rutland
2015-10-13T14:22:40Z

On Tue, Oct 13, 2015 at 04:00:45PM +0200, M'boumba Cedric Madianga wrote:
> This patch adds documentation of device tree bindings for the STM32 dma
> controller.
>
> Signed-off-by: M'boumba Cedric Madianga <cedric.madianga@gmail.com>
> ---
> .../devicetree/bindings/dma/stm32-dma.txt | 98 ++++++++++++++++++++++
> 1 file changed, 98 insertions(+)
> create mode 100644 Documentation/devicetree/bindings/dma/stm32-dma.txt
>
> diff --git a/Documentation/devicetree/bindings/dma/stm32-dma.txt b/Documentation/devicetree/bindings/dma/stm32-dma.txt
> new file mode 100644
> index 0000000..9ce0d49
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/dma/stm32-dma.txt
> @@ -0,0 +1,98 @@
> +* STMicroelectronics STM32 DMA controller
> +
> +The STM32 DMA is a general-purpose direct memory access controller capable of
> +supporting 8 independent DMA channels. Each channel can have up to 8 requests.
> +
> +Required properties:
> +- compatible: Should be "st,stm32-dma"
> +- reg: Should contain DMA registers location and length. This should include
> + all of the per-channel registers.
> +- interrupts: Should contain all of the per-channel DMA interrupts.

Please specify the order they must be in.

> +- clocks: Should contain the input clock of the DMA instance.
> +- #dma-cells : Must be <4>. See DMA client paragraph for more details.
> +
> +Optional properties:
> +- resets: Reference to a reset controller asserting the DMA controller
> +- st,mem2mem: boolean; if defined, it indicates that the controller supports
> + memory-to-memory transfer
> +
> +Example:
> +
> + dma2: dma-controller at 40026400 {
> + compatible = "st,stm32-dma";
> + reg = <0x40026400 0x400>;
> + interrupts = <56>,
> + <57>,
> + <58>,
> + <59>,
> + <60>,
> + <68>,
> + <69>,
> + <70>;
> + clocks = <&clk_hclk>;
> + #dma-cells = <4>;
> + st,mem2mem;
> + resets = <&rcc 150>;
> + };
> +
> +* DMA client
> +
> +Required properties:
> +- dmas: Comma separated list of dma channel requests
> +- dma-names: Names of the aforementioned requested channels
> +
> +Each dmas request consists of 5 cells:
> +1. A phandle pointing to the STM32 DMA controller
> +2. The channel id
> +3. The request line number
> +4. A 32bit mask specifying the DMA channel configuration
> + -bit 1: Direct Mode Error Interrupt
> + 0x0: disabled
> + 0x1: enabled
> + -bit 2: Transfer Error Interrupt
> + 0x0: disabled
> + 0x1: enabled
> + -bit 3: Half Transfer Mode Error Interrupt
> + 0x0: disabled
> + 0x1: enabled
> + -bit 4: Transfer Complete Interrupt
> + 0x0: disabled
> + 0x1: enabled

Why should this be in the DT?

Surely the driver should be in charge of deciding when to use these?

> + -bit 9: Peripheral Increment Address
> + 0x0: no address increment between transfers
> + 0x1: increment address between transfers
> + -bit 10: Memory Increment Address
> + 0x0: no address increment between transfers
> + 0x1: increment address between transfers

These don't seem like they belong either. Surely this would depend on
the request made, rather than being a fixed property?

> + -bit 15: Peripheral Increment Offset Size
> + 0x0: offset size is linked to the peripheral bus width
> + 0x1: offset size is fixed to 4 (32-bit alignment)

This sounds like it might belong in the DT.

> + -bit 16-17: Priority level
> + 0x0: low
> + 0x1: medium
> + 0x2: high
> + 0x3: very high

What do we do elsewhere in terms of describing prioritisation? It feels
like it would be a dynamic property of the system.

> +5. A 32bit mask specifying the DMA FIFO configuration
> + -bit 0-1: Fifo threshold
> + 0x0: 1/4 full FIFO
> + 0x1: 1/2 full FIFO
> + 0x2: 3/4 full FIFO
> + 0x3:full FIFO

What does this mean?

> + -bit 2: Direct mode
> + 0x0: enabled
> + 0x1: disabled

What does this mean?

> + -bit 7: FIFO Error Interrupt
> + 0x0: disabled
> + 0x1: enabled

As with the other interrupt configuration, this does not look like it
belongs in the DT.

Thanks,
Mark.