Re: [PATCH 09/13] dt-bindings: phy: Add documentation for Airoha AN7581 USB PHY

Christian Marangi
2025-03-18T11:31:07Z

On Sun, Mar 16, 2025 at 06:01:02PM +0100, Krzysztof Kozlowski wrote:
> On 11/03/2025 19:51, Christian Marangi wrote:
> >>
> >>> + $ref: /schemas/types.yaml#/definitions/uint32
> >>> + enum: [0, 1]
> >>
> >> I don't understand why do you need index property here (which are
> >> usually not allowed).
> >>
> >
> > Eh... As said in the description this is really to differentiate the 2
> > different physical port...
> >
> > Each port have a dedicated oscillator for calibration and these
> > calibration are identified by an offset (all placed one after another in
> > a separate register space).
>
> So different oscillators? Then describe the oscillator and its differences.
>
> Different programing model? Different compatible.
>
> Other difference? Depending what is the difference.
>
> But there is no such thing as "different port ID" based on your
> description above. You just claimed that they are different, but you do
> not put that difference to hardware description. Instead you encode that
> difference in the drivers and it should be opposite. The DTS, so the
> hardware description, should tell you the difference. And I am sorry,
> but in 99% of cases "I am the first phy" and "I am the second" is not
> the actual difference we are interested in.
>

Ok to make it as clear as possible. (hope I don't contraddict with the
previous statement) (actually yes the "separate register space statement
was wrong and sorry for the confusion")

- 2 USB port
- USB 2.0 needs to be calibrated with an oscillator
- Each USB port have his own dedicated oscillator somewhere in the HW
- Each USB port have at the same offset a register to SELECT the
oscillator. This register refer to the same oscillator selection in
the HW.

Example:
reg 0x1fac0100 MASK 27:26 can be set to source out of oscillator 0,1,2
reg 0x1fae0100 MASK 27:26 can be set to source out of oscillator 0,1,2

Both register refer to the same oscillators in hardware (hence each
port should select the correct one)
Selecting oscillator 0 for both USB port is problematic.

With this in mind is it ok if I describe this with something like

airoha,usb2-monitor-clk-sel = <AIROHA_USB2_MONCLK_SEL0>;

and some dt-bindings include

#define AIROHA_USB2_MONCLK_SEL0 0
#define AIROHA_USB2_MONCLK_SEL1 1
#define AIROHA_USB2_MONCLK_SEL2 2
#define AIROHA_USB2_MONCLK_SEL3 3

Or an enum of string like "osc0", "osc1", "osc2"...?

> >
> > Oscillator 0 for physical port 0
> > Oscillator 1 for physcial port 1
> >
> > And model this is a bit problematic without an additional property, any
> > hint for this?
> >
> Best regards,
> Krzysztof

--
Ansuel