Re: [PATCH v2 2/7] dt-bindings: clock: renesas,r9a06g032-sysctrl: Add h2mode property

[Herve Codina]

Hi Krzysztof, Geert,

On Tue, 15 Nov 2022 15:04:17 +0100
Herve Codina <herve.codina@xxxxxxxxxxx> wrote:

> Hi Krzysztof,
> 
> On Tue, 15 Nov 2022 14:07:52 +0100
> Krzysztof Kozlowski <krzysztof.kozlowski@xxxxxxxxxx> wrote:
> 
> > On 15/11/2022 14:05, Krzysztof Kozlowski wrote:  
> > > On 14/11/2022 12:15, Herve Codina wrote:    
> > >> Add the h2mode property to force the USBs mode ie:
> > >>  - 2 hosts
> > >> or
> > >>  - 1 host and 1 device
> > >>
> > >> Signed-off-by: Herve Codina <herve.codina@xxxxxxxxxxx>
> > >> ---
> > >>  .../bindings/clock/renesas,r9a06g032-sysctrl.yaml      | 10 ++++++++++
> > >>  1 file changed, 10 insertions(+)
> > >>
> > >> diff --git a/Documentation/devicetree/bindings/clock/renesas,r9a06g032-sysctrl.yaml b/Documentation/devicetree/bindings/clock/renesas,r9a06g032-sysctrl.yaml
> > >> index 95bf485c6cec..f9e0a58aa4fb 100644
> > >> --- a/Documentation/devicetree/bindings/clock/renesas,r9a06g032-sysctrl.yaml
> > >> +++ b/Documentation/devicetree/bindings/clock/renesas,r9a06g032-sysctrl.yaml
> > >> @@ -39,6 +39,16 @@ properties:
> > >>    '#power-domain-cells':
> > >>      const: 0
> > >>  
> > >> +  renesas,h2mode:
> > >> +    description: |
> > >> +      Configure the USBs mode.
> > >> +        - <0> : the USBs are in 1 host and 1 device mode.
> > >> +        - <1> : the USBs are in 2 host mode.
> > >> +      If the property is not present, the value used is the one already present
> > >> +      in the CFG_USB register (from reset or set by the bootloader).
> > >> +    $ref: /schemas/types.yaml#/definitions/uint32
> > >> +    enum: [0, 1]    
> > > 
> > > 0/1 are quite cryptic. Why not making it a string which is easy to read
> > > and understand? Can be something like "two-hosts" and "one-host". Or
> > > anything you find more readable...    
> > 
> > ...but actually you should rather make it a property of your USB
> > controller, not clock controller. You have two controllers and we have a
> > generic property for them - dr_mode.
> > 
> > Best regards,
> > Krzysztof
> >   
> 
> IMHO, this property in the USB controllers does not make sense.
> Indeed each controller cannot have a different 'mode'.
> Some controllers are USB host only (EHCI and OHCI) and the USBF
> controller I worked on is device only.
> 'h2mode' allows to choose between host or device on one of the USB
> but not at the USB controller level.
> 
> This property should be handle outside the USB controller nodes.
> 
> Currently, this node (declared as a clock node) is in fact a sysctrl
> node and can do some configuration not related to clocks.
> 
> I agree with you something related to choosing USB Host/Device in
> a clock node seems strange.
> 
> Some discussion were already opened related to this property and how
> to handle it:
>   https://lore.kernel.org/all/20221107182642.05a09f2f@xxxxxxxxxxx/
>   https://lore.kernel.org/all/20221107173614.474707d7@xxxxxxxxxxx/
> 

We advanced on this topic.

First, even if 'renesas,r9a06g032-sysctrl.yaml' is present in
the devicetree/bindings/clock/ directory, this node is really
a 'system controller' node:
- title: Renesas RZ/N1D (R9A06G032) System Controller
- compatible: renesas,r9a06g032-sysctrl

It handles clocks, power domains, some DMA routing, ...

Now, the property 'h2mode' allows to choose between:
  - 2 USB hosts
or
  - 1 USB host and 1 USB device.

This switching is system wide and has no reason to be done in
one specific USB controller. It can impact multiple devices and
PLL settings.

The 'renesas,r9a06g032-sysctrl' node, as the system control
node of our system, is the best candidate to handle the property.

In order to be less cryptic in the property value, what do you
think about:
  renesas,h2mode:
    - one-dev : the USBs are in 1 host and 1 device mode.
    - only-hosts : the USBs are in 2 hosts mode.

With these details and change on the property value,
Is it ok for you to have the 'renesas,h2mode' property
in the 'renesas,r9a06g032-sysctrl' node ?


Regards,
Hervé

-- 
Hervé Codina, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com