Re: [PATCH net-next 5/5] arm64: dts: ti: k3-am625-sk: Add cpsw3g cpts PPS support

[Roger Quadros <rogerq@kernel.org>]

On 16/01/2023 09:12, Siddharth Vadapalli wrote:
> Roger,
> 
> On 13/01/23 15:48, Roger Quadros wrote:
>> Hi,
>>
>> On 11/01/2023 13:44, Siddharth Vadapalli wrote:
>>> The CPTS driver is capable of configuring GENFy (Periodic Signal Generator
>>> Function) present in the CPTS module, to generate periodic output signals
>>> with a custom time period. In order to generate a PPS signal on the GENFy
>>> output, the device-tree property "ti,pps" has to be used. The "ti,pps"
>>> property is used to declare the mapping between the CPTS HWx_TS_PUSH
>>> (Hardware Timestamp trigger) input and the GENFy output that is configured
>>> to generate a PPS signal. The mapping is of the form:
>>> <x-1 y>
>>> where the value x corresponds to HWx_TS_PUSH input (1-based indexing) and
>>> the value y corresponds to GENFy (0-based indexing).
>>
>> You mean there is no HWx_TX_PUSH0 pin? so user needs to use 0 for HWx_TX_PUSH1 pin?
> 
> The HWx_TX_PUSH pins correspond to the cpts_hw1_push, cpts_hw2_push,...,
> cpts_hw8_push pins. The names are documented at:
> 
> Link:
> https://software-dl.ti.com/tisci/esd/latest/5_soc_doc/am62x/interrupt_cfg.html#timesync-event-router0-interrupt-router-output-destinations
> 
> Thus, considering that the documentation uses 1-based indexing, I wanted to
> indicate that the driver expects 0-based indexing, and therefore the user would
> have to provide (x-1) for cpsw_hwx_push pin.
> 
>>
>> Can you please define macros for HWx_TS_PUSH and GENFy so we avoid
>> human error with this different indexing methods?
>>
>> DT should contain the name exactly in hardware.
>>
>> So if pin is called HWx_TX_PUSH1 in hardware then DT should contain HWx_TX_PUSH(1).
> 
> The pins are called HW1_TX_PUSH, HW2_TX_PUSH and so on. This 1-based indexing is
> followed in the Technical Reference Manual. Similarly, the documentation in the
> link above also uses 1-based indexing: cpts_hw1_push, cpts_hw2_push, and so on.
> 
> However, for the GENFy pins, the documentation consistently uses 0-based
> indexing. Thus, the driver expects indices that are 0-based and the user is
> expected to convert the x to x-1 for the HWx_TX_PUSH pins while the y in GENFy
> pins can be used directly as it is already 0-based indexing.
> 
>>
>>>
>>> To verify that the signal is a PPS signal, the GENFy output signal is fed
>>> into the CPTS HWx_TS_PUSH input, which generates a timestamp event on the
>>> rising edge of the GENFy signal. The GENFy output signal can be routed to
>>> the HWx_TS_PUSH input by using the Time Sync Router. This is done by
>>> mentioning the mapping between the GENFy output and the HWx_TS_PUSH input
>>> within the "timesync_router" device-tree node.
>>>
>>> The Input Sources to the Time Sync Router are documented at: [1]
>>> The Output Destinations of the Time Sync Router are documented at: [2]
>>>
>>> The PPS signal can be verified using testptp and ppstest tools as follows:
>>>  # ./testptp -d /dev/ptp0 -P 1
>>>  pps for system time request okay
>>>  # ./ppstest /dev/pps0
>>>  trying PPS source "/dev/pps0"
>>>  found PPS source "/dev/pps0"
>>>  ok, found 1 source(s), now start fetching data...
>>>  source 0 - assert 48.000000013, sequence: 8 - clear  0.000000000, sequence: 0
>>>  source 0 - assert 49.000000013, sequence: 9 - clear  0.000000000, sequence: 0
>>>  source 0 - assert 50.000000013, sequence: 10 - clear  0.000000000, sequence: 0
>>>
>>> Add an example in the device-tree, enabling PPS generation on GENF1. The
>>> HW3_TS_PUSH Timestamp trigger input is used to verify the PPS signal.
>>>
>>> [1]
>>> Link: https://software-dl.ti.com/tisci/esd/latest/5_soc_doc/am62x/interrupt_cfg.html#timesync-event-router0-interrupt-router-input-sources
>>> [2]
>>> Link: https://software-dl.ti.com/tisci/esd/latest/5_soc_doc/am62x/interrupt_cfg.html#timesync-event-router0-interrupt-router-output-destinations
>>>
>>> Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
>>> ---
>>>  arch/arm64/boot/dts/ti/k3-am625-sk.dts | 20 ++++++++++++++++++++
>>>  1 file changed, 20 insertions(+)
>>>
>>> diff --git a/arch/arm64/boot/dts/ti/k3-am625-sk.dts b/arch/arm64/boot/dts/ti/k3-am625-sk.dts
>>> index 4f179b146cab..962a922cc94b 100644
>>> --- a/arch/arm64/boot/dts/ti/k3-am625-sk.dts
>>> +++ b/arch/arm64/boot/dts/ti/k3-am625-sk.dts
>>> @@ -366,6 +366,10 @@ &cpsw3g {
>>>  	pinctrl-names = "default";
>>>  	pinctrl-0 = <&main_rgmii1_pins_default
>>>  		     &main_rgmii2_pins_default>;
>>> +
>>> +	cpts@3d000 {
>>> +		ti,pps = <2 1>;
>>> +	};
>>>  };
>>>  
>>>  &cpsw_port1 {
>>> @@ -464,3 +468,19 @@ partition@3fc0000 {
>>>  		};
>>>  	};
>>>  };
>>> +
>>> +#define TS_OFFSET(pa, val)	(0x4+(pa)*4) (0x10000 | val)
>>
>> Should this go in ./include/dt-bindings/pinctrl/k3.h ?
>> That way every board DT file doesn't have to define it.
>>
>> The name should be made more platform specific.
>> e.g. K3_TS_OFFSET if it is the same for all K3 platforms.
>> If not then please add Platform name instead of K3.
> 
> The offsets are board specific. If it is acceptable, I will add board specific
> macro for the TS_OFFSET definition in the ./include/dt-bindings/pinctrl/k3.h
> file. Please let me know.

If it is board specific then it should remain in the board file.

cheers,
-roger