On 9/9/24 9:03 AM, Nuno Sá wrote:
> On Mon, 2024-09-09 at 13:46 +0100, Conor Dooley wrote:
>> On Sun, Sep 08, 2024 at 01:29:25PM +0100, Jonathan Cameron wrote:
>>> On Thu, 05 Sep 2024 17:17:31 +0200
>>> Angelo Dureghello <adureghello@xxxxxxxxxxxx> wrote:
>>>
>>>> From: Angelo Dureghello <adureghello@xxxxxxxxxxxx>
>>>>
>>>> There is a version AXI DAC IP block (for FPGAs) that provides
>>>> a physical bus for AD3552R and similar chips. This can be used
>>>> instead of a typical SPI controller to be able to use the chip
>>>> in ways that typical SPI controllers are not capable of.
>>>>
>>>> The binding is modified so that either the device is a SPI
>>>> peripheral or it uses an io-backend.
>>>>
>>>> Signed-off-by: Angelo Dureghello <adureghello@xxxxxxxxxxxx>
>>>
>>>>
>>>> required:
>>>> - compatible
>>>> - - reg
>>>> - - spi-max-frequency
>>> Sort of feels like both reg and spi-max-frequency
>>> are valid things to specify.
>>>
>>> Maybe we have an excellent IP and dodgy wiring so want
>>> to clamp the frequency (long term - don't need to support
>>> in the driver today).
>>>
>>> Maybe we have an axi_dac IP that supports multiple
>>> front end devices? So maybe just keep reg?
>>
>> I'd like to be convinced that this incarnation of the AXI DAC IP is not
>> a spi controller and that a ref to spi-controller.yaml is not out of
>> place here. It may not be something that you'd ever use generally, given
>> the "weird" interface to it, but it does seem to be one regardless.
>>
>
> Agreed.. As weird as it get's, it's acting as a spi controller.
>
>> I'd also really like to know how this fits in with spi-offloads. It
>> /feels/, and I'd like to reiterate the word feels, like a rather similar
>> idea just applied to a DAC instead of an ADC.
>
> The offload main principle is to replay a spi transfer periodically given an
> input trigger. I'm not so sure we have that same principle in here. In here I
> guess we stream data over the qspi interface based on SCLK which can look
> similar. The difference is that this IP does not need any trigger for any spi
> transfer replay (I think).
>
Looking at the AD3552R from a SPI offload perspective of triggered SPI
messages, I think it still works.
The trigger doesn't have to be a clock/PWM. In this case, the trigger would
be whenever the IIO buffer is full and ready to send a burst of data (not
sure if this would be a hardware or software trigger - but it works either
way).
Also, the DAC_CUSTOM_CTRL::ADDRESS register field in the AXI DAC IP core
acts as an offload to record and play back a SPI write transfer.
If we were using the AXI SPI Engine, this would be one SPI message with
two xfers, one for the address write followed by one for the data write.
The size of the data write would be the size of the IIO buffer - or in
the case of a cyclic DMA, the size of the write data would be channel
data size * num channels and the xfer would have a special cyclic offload
flag set.
So I think we could make a single binding that works for the the AXI DAC
backend/offload and the AXI SPI Engine offload. (I don't think it would
be so easy to integrate the AXI DAC into the SPI framework on the driver
side - and hopefully we won't have to, but the DT still could use the
proposed SPI offload bindings.)
axi_dac: spi@44a70000 {
compatible = "adi,axi-ad3225r";
reg = <0x44a70000 0x1000>;
dmas = <&dac_tx_dma_1 0>;
dma-names = "tx";
clocks = <&ref_clk>;
#spi-offload-cells = <0>;
#address-cells = <1>;
#size-cells = <0>;
dac@0 {
compatible = "adi,ad3552r";
reg = <0>;
spi-max-frequency = <30000000>;
spi-3-wire;
spi-tx-bus-width = <4>;
spi-rx-bus-width = <4>;
reset-gpios = <&gpio0 92 GPIO_ACTIVE_LOW>;
spi-offloads = <&axi_dac>;
#address-cells = <1>;
#size-cells = <0>;
channel@0 {
reg = <0>;
adi,output-range-microvolt = <(-10000000) (10000000)>;
};
};
};
axi_spi_engine: spi@44a80000 {
compatible = "adi,axi-spi-engine-1.00.a";
reg = <0x44a80000 0x1000>;
dmas = <&dac_tx_dma_2 0>;
dma-names = "offload0-tx";
clocks = <&ref_clk>;
#spi-offload-cells = <1>;
#address-cells = <1>;
#size-cells = <0>;
dac@0 {
compatible = "adi,ad3552r";
reg = <0>;
spi-max-frequency = <30000000>;
spi-3-wire;
spi-tx-bus-width = <4>;
spi-rx-bus-width = <4>;
reset-gpios = <&gpio0 92 GPIO_ACTIVE_LOW>;
spi-offloads = <&axi_spi_engine 0>;
#address-cells = <1>;
#size-cells = <0>;
channel@0 {
reg = <0>;
adi,output-range-microvolt = <(-10000000) (10000000)>;
};
};
};
