Hi Andy,
On 12/05/2018 04:11 PM, Andy Shevchenko wrote:
> For the platforms which have no clock provider for the sc16is7xx type of UART,
> introduce an alternative clock-frequency property which would be used instead.
the subject has a typo in 'clock-frequence', then can you please tell me more,
how is it possible that an SC16IS7xx IC has no clock provider connected to it?
And if there is one, then please just describe it in device tree as well.
>
> Cc: Rob Herring <robh+dt@xxxxxxxxxx>
> Cc: devicetree@xxxxxxxxxxxxxxx
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> ---
> Documentation/devicetree/bindings/serial/nxp,sc16is7xx.txt | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/serial/nxp,sc16is7xx.txt b/Documentation/devicetree/bindings/serial/nxp,sc16is7xx.txt
> index e7921a8e276b..b8cf38a1e43c 100644
> --- a/Documentation/devicetree/bindings/serial/nxp,sc16is7xx.txt
> +++ b/Documentation/devicetree/bindings/serial/nxp,sc16is7xx.txt
> @@ -12,6 +12,8 @@ Required properties:
> - reg: I2C address of the SC16IS7xx device.
> - interrupts: Should contain the UART interrupt
> - clocks: Reference to the IC source clock.
> + OR
> +- clock-frequency: The source clock frequency for the IC.
>
I strongly dislike this change, I'm inclined to cast a NAK to the series.
1. 'clock-frequency' is a very specific device tree property, in my opinion
its presence is justified on sort of clock provider devices only (like I2C
controllers), unfortunately the property was added to a number of device
tree bindings improperly, mainly it was done before introduction of
"assigned-clocks" and "assigned-clock-parents" properties in CCF, and then
it was blindly copied.
2. SC16IS7xx type of UARTs is a regular clock consumer, ICs always have a valid
clock provider connected to XTAL1 (and XTAL2 in case of a connected
crystal oscillator), thus, if needed, the driver can get input clock rate
by calling standard clk_get_rate(), so the presence of the required 'clocks'
property is sufficient.
3. In some very specific corner cases it might be needed to add another
"assigned-clocks" and "assigned-clock-parents" properties to a particular
device node on a particular board, but their explicit description in device
tree bindings is not needed.
--
Best wishes,
Vladimir
> Optional properties:
> - gpio-controller: Marks the device node as a GPIO controller.
>
