On Sun, 2024-09-29 at 11:59 +0100, Jonathan Cameron wrote: > On Sat, 28 Sep 2024 14:20:29 +0200 > Krzysztof Kozlowski <krzk@xxxxxxxxxx> wrote: > > > On 25/09/2024 13:55, Nuno Sá wrote: > > > On Wed, 2024-09-25 at 09:22 +0200, Krzysztof Kozlowski wrote: > > > > On 24/09/2024 14:27, Nuno Sá wrote: > > > > > On Tue, 2024-09-24 at 10:02 +0200, Krzysztof Kozlowski wrote: > > > > > > On 23/09/2024 17:50, Angelo Dureghello wrote: > > > > > > > Hi Krzysztof, > > > > > > > > > > > > > > On 22/09/24 23:02, Krzysztof Kozlowski wrote: > > > > > > > > On Thu, Sep 19, 2024 at 11:20:00AM +0200, Angelo Dureghello > > > > > > > > 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, and acts as > > > > > > > > > an SPI controller. > > > > > > > > > > > > > > > > > > For this case, the binding is modified to include some > > > > > > > > > additional properties. > > > > > > > > > > > > > > > > > > Signed-off-by: Angelo Dureghello <adureghello@xxxxxxxxxxxx> > > > > > > > > > --- > > > > > > > > > .../devicetree/bindings/iio/dac/adi,ad3552r.yaml | 42 > > > > > > > > > ++++++++++++++++++++++ > > > > > > > > > 1 file changed, 42 insertions(+) > > > > > > > > > > > > > > > > > > diff --git > > > > > > > > > a/Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml > > > > > > > > > b/Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml > > > > > > > > > index 41fe00034742..aca4a41c2633 100644 > > > > > > > > > --- > > > > > > > > > a/Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml > > > > > > > > > +++ > > > > > > > > > b/Documentation/devicetree/bindings/iio/dac/adi,ad3552r.yaml > > > > > > > > > @@ -60,6 +60,18 @@ properties: > > > > > > > > > $ref: /schemas/types.yaml#/definitions/uint32 > > > > > > > > > enum: [0, 1, 2, 3] > > > > > > > > > > > > > > > > > > + io-backends: > > > > > > > > > + description: The iio backend reference. > > > > > > > > > + An example backend can be found at > > > > > > > > > + > > > > > > > > > https://analogdevicesinc.github.io/hdl/library/axi_ad3552r/index.html > > > > > > > > > + maxItems: 1 > > > > > > > > > + > > > > > > > > > + adi,synchronous-mode: > > > > > > > > > + description: Enable waiting for external synchronization > > > > > > > > > signal. > > > > > > > > > + Some AXI IP configuration can implement a dual-IP > > > > > > > > > layout, > > > > > > > > > with > > > > > > > > > internal > > > > > > > > > + wirings for streaming synchronization. > > > > > > > > > + type: boolean > > > > > > > > > + > > > > > > > > > '#address-cells': > > > > > > > > > const: 1 > > > > > > > > > > > > > > > > > > @@ -128,6 +140,7 @@ patternProperties: > > > > > > > > > - custom-output-range-config > > > > > > > > > > > > > > > > > > allOf: > > > > > > > > > + - $ref: /schemas/spi/spi-peripheral-props.yaml# > > > > > > > > > - if: > > > > > > > > > properties: > > > > > > > > > compatible: > > > > > > > > > @@ -238,4 +251,33 @@ examples: > > > > > > > > > }; > > > > > > > > > }; > > > > > > > > > }; > > > > > > > > > + > > > > > > > > > + - | > > > > > > > > > + axi_dac: spi@44a70000 { > > > > > > > > > + compatible = "adi,axi-ad3552r"; > > > > > > > > That is either redundant or entire example should go to the > > > > > > > > parent > > > > > > > > node, > > > > > > > > if this device is fixed child of complex device (IOW, > > > > > > > > adi,ad3552r > > > > > > > > cannot > > > > > > > > be used outside of adi,axi-ad3552r). > > > > > > > > > > > > > > ad3552r can still be used by a generic "classic" spi > > > > > > > controller (SCLK/CS/MISO) but at a slower samplerate, fpga > > > > > > > controller only (axi-ad3552r) can reach 33MUPS. > > > > > > > > > > > > OK, then this is just redundant. Drop the node. Parent example > > > > > > should > > > > > > contain the children, though. > > > > > > > > > > > > > > > > > > > > > > > > + reg = <0x44a70000 0x1000>; > > > > > > > > > + dmas = <&dac_tx_dma 0>; > > > > > > > > > + dma-names = "tx"; > > > > > > > > > + #io-backend-cells = <0>; > > > > > > > > > + clocks = <&ref_clk>; > > > > > > > > > + > > > > > > > > > + #address-cells = <1>; > > > > > > > > > + #size-cells = <0>; > > > > > > > > > + > > > > > > > > > + dac@0 { > > > > > > > > > + compatible = "adi,ad3552r"; > > > > > > > > > + reg = <0>; > > > > > > > > > + reset-gpios = <&gpio0 92 0>; > > > > > > > > Use standard defines for GPIO flags. > > > > > > > > > > > > > > fixed, thanks > > > > > > > > > > > > > > > > + io-backends = <&axi_dac>; > > > > > > > > Why do you need to point to the parent? How much coupled are > > > > > > > > these > > > > > > > > devices? Child pointing to parent is not usually expected, > > > > > > > > because > > > > > > > > that's obvious. > > > > > > > > > > > > > > > > > > > > > "io-backends" is actually the way to refer to the backend module, > > > > > > > (used already for i.e. ad9739a), > > > > > > > it is needed because the backend is not only acting as spi- > > > > > > > controller, > > > > > > > but is also providing some APIs for synchronization and bus setup > > > > > > > support. > > > > > > > > > > > > > > > > > > But if backend is the parent, then this is redundant. You can take > > > > > > it > > > > > > from the child-parent relationship. Is this pointing to other > > > > > > devices > > > > > > (non-parent) in other ad3552r configurations? > > > > > > > > > > > > > > > > The backend is a provider-consumer type of API. On the consumer side > > > > > (which > > > > > is the > > > > > driver the child node will probe on), we need to call > > > > > devm_iio_backend_get() > > > > > to get > > > > > the backend object (which obviously is the parent). For that, 'io- > > > > > backends' > > > > > is being > > > > > > > > You described the driver, so how does it matter? Driver can call > > > > get_backend_from_parent(), right? Or get_backend_from_fwnode(parent)? > > > > > > Well yes, just stating what the framework (also in terms of bindings) is > > > expecting. Of course that on the driver side we can paper around it the > > > way we > > > want. But my main point was that we can only paper around it if we use > > > code that > > > is meant not to be used. > > > > > > And, FWIW, I was (trying) replying to your comment > > > > > > "You can take it from the child-parent relationship" > > > > > > Again, we can only do that by introducing new code or use code that's not > > > meant > > > to be used. The way we're supposed to reference backends is by explicitly > > > using > > > the proper FW property. > > > > > > Put it in another way and a completely hypothetical case. If we have a spi > > > controller which happens to export some clock and one of it's peripherals > > > ends > > > up using that clock, wouldn't we still use 'clocks' to reference that > > > clock? > > > > I asked how coupled are these devices. Never got the answer and you are > > reflecting with question. Depends. Please do not create hypothetical, > > generic scenarios and then apply them to your one particular opposite case. > > I'll throw a possible clarifying question in here. Could we use this > device with a multimaster SPI setup such that the control is on a conventional > SPI controller (maybe a qspi capable one), and the data plane only goes > through > a specific purpose backend? If so, then they are not tightly coupled and > the reference makes sense. Putting it another way, the difference between > this case and all the prior iio-backend bindings is the control and dataplanes > use the same pins. Does that have to be the case at the host end? If it > does, > then the reference isn't strictly needed and this becomes a bit like > registering a single device on an spi bus or an i2c bus depending on who > does the registering (which is down to the parent in DT). > So, we currently have two drivers (with a new one being added in this series) for the same device: 1) A SPI one tied to a typical spi controller. This is the "low speed" implementation and does not use backends; 2) The new platform device that is connected like this to the backend. So yes, my understanding (but Angelo should know better :)) is that they are tightly coupled. Putting it in another way, the new platform device is very much specific to this parent (and yeah, this is a very special usecase where control and data planes are controlled by the IIO backend) and should not exist with it. - Nuno Sá
