Re: [PATCH 1/2] dt-bindings: Document the STM32 MDMA bindings

["M'boumba Cedric Madianga" <cedric.madianga@gmail.com>]

Hi Rob,

2017-03-20 22:52 GMT+01:00 Rob Herring <robh@kernel.org>:
> On Mon, Mar 13, 2017 at 04:06:38PM +0100, M'boumba Cedric Madianga wrote:
>> This patch adds documentation of device tree bindings for the STM32 MDMA
>> controller.
>>
>> Signed-off-by: M'boumba Cedric Madianga <cedric.madianga@gmail.com>
>> Reviewed-by: Ludovic BARRE <ludovic.barre@st.com>
>> ---
>>  .../devicetree/bindings/dma/stm32-mdma.txt         | 94 ++++++++++++++++++++++
>>  1 file changed, 94 insertions(+)
>>  create mode 100644 Documentation/devicetree/bindings/dma/stm32-mdma.txt
>>
>> diff --git a/Documentation/devicetree/bindings/dma/stm32-mdma.txt b/Documentation/devicetree/bindings/dma/stm32-mdma.txt
>> new file mode 100644
>> index 0000000..26a930c
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/dma/stm32-mdma.txt
>> @@ -0,0 +1,94 @@
>> +* STMicroelectronics STM32 MDMA controller
>> +
>> +The STM32 MDMA is a general-purpose direct memory access controller capable of
>> +supporting 64 independent DMA channels with 256 HW requests.
>> +
>> +Required properties:
>> +- compatible: Should be "st,stm32-mdma"
>
> Should be more specific.

The compatible string is not specific enough ? I don't see how to specific more.

>
>> +- reg: Should contain MDMA registers location and length. This should include
>> +  all of the per-channel registers.
>> +- interrupts: Should contain the MDMA interrupt.
>> +- clocks: Should contain the input clock of the DMA instance.
>> +- resets: Reference to a reset controller asserting the DMA controller.
>> +- #dma-cells : Must be <5>. See DMA client paragraph for more details.
>> +
>> +Optional properties:
>> +- dma-channels: Number of DMA channels supported by the controller.
>> +- dma-requests: Number of DMA request signals supported by the controller.
>> +- st,ahb-addr-masks: Array of u32 mask to list memory devices addressed via
>> +  AHB bus.
>
> I don't understand what this is.

The MDMA is able to address memories and devices from AHB bus or AXI bus.
The MDMA has a little different way of working to address AHB
device/memory and AXI device/memory.
In STM32H7 platform, almost all devices are addressed by AXI bus.
But we have some memories adress by AHB bus.
So, we add these parameter to be able to handle this.

>
>> +
>> +Example:
>
> Put the 2 examples together.

OK

>
>> +
>> +     mdma1: dma@52000000 {
>> +             compatible = "st,stm32-mdma";
>> +             reg = <0x52000000 0x1000>;
>> +             interrupts = <122>;
>> +             clocks = <&clk_dummy>;
>> +             resets = <&rcc 992>;
>> +             #dma-cells = <5>;
>> +             dma-channels = <16>;
>> +             dma-requests = <32>;
>> +             st,ahb-addr-masks = <0x20000000>, <0x00000000>;
>> +     };
>> +
>> +* DMA client
>> +
>> +DMA clients connected to the STM32 MDMA controller must use the format
>> +described in the dma.txt file, using a six-cell specifier for each channel:
>> +a phandle to the MDMA controller plus the following five integer cells:
>> +
>> +1. The request line number
>> +2. The priority level
>> +     0x00: Low
>> +     0x01: Medium
>> +     0x10: High
>> +     0x11: Very high
>> +3. A 32bit mask specifying the DMA channel configuration
>> + -bit 0-1: Source increment mode
>> +     0x00: Source address pointer is fixed
>> +     0x10: Source address pointer is incremented after each data transfer
>> +     0x11: Source address pointer is decremented after each data transfer
>> + -bit 2-3: Destination increment mode
>> +     0x00: Destination address pointer is fixed
>> +     0x10: Destination address pointer is incremented after each data
>> +     transfer
>> +     0x11: Destination address pointer is decremented after each data
>> +     transfer
>> + -bit 8-9: Source increment offset size
>> +     0x00: byte (8bit)
>> +     0x01: half-word (16bit)
>> +     0x10: word (32bit)
>> +     0x11: double-word (64bit)
>> + -bit 10-11: Destination increment offset size
>> +     0x00: byte (8bit)
>> +     0x01: half-word (16bit)
>> +     0x10: word (32bit)
>> +     0x11: double-word (64bit)
>> +-bit 25-18: The number of bytes to be transferred in a single transfer
>> +     (min = 1 byte, max = 128 bytes)
>> +-bit 29:28: Trigger Mode
>> +     0x00: Each MDMA request triggers a buffer transfer (max 128 bytes)
>> +     0x01: Each MDMA request triggers a block transfer (max 64K bytes)
>> +     0x10: Each MDMA request triggers a repeated block transfer
>> +     0x11: Each MDMA request triggers a linked list transfer
>> +4. A 32bit value specifying the register to be used to acknowledge the request
>> +   if no HW ack signal is used by the MDMA client
>> +5. A 32bit mask specifying the value to be written to acknowledge the request
>> +   if no HW ack signal is used by the MDMA client
>> +
>> +Example:
>> +
>> +     i2c4: i2c@5c002000 {
>> +             compatible = "st,stm32f7-i2c";
>> +             reg = <0x5c002000 0x400>;
>> +             interrupts = <GIC_SPI 95 IRQ_TYPE_NONE>,
>> +                          <GIC_SPI 96 IRQ_TYPE_NONE>;
>> +             clocks = <&clk_hsi>;
>> +             #address-cells = <1>;
>> +             #size-cells = <0>;
>> +             dmas = <&mdma1 36 0x0 0x40008 0x0 0x0>,
>> +                    <&mdma1 37 0x0 0x40002 0x0 0x0>;
>> +             dma-names = "rx", "tx";
>> +             status = "disabled";
>> +     };
>> --
>> 1.9.1
>>