linux-kernel - Re: [PATCH v2 4/6] firmware: arm_scmi: add SCMIv3.0 Sensors timestamped reads

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Date:   Tue, 10 Nov 2020 18:14:44 +0100
From:   Peter Hilber <peter.hilber@...nsynergy.com>
To:     Cristian Marussi <cristian.marussi@....com>
CC:     <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>, <sudeep.holla@....com>,
        <lukasz.luba@....com>, <james.quinlan@...adcom.com>,
        <Jonathan.Cameron@...wei.com>, <egranata@...gle.com>,
        <jbhayana@...gle.com>, <mikhail.golubev@...nsynergy.com>,
        <Igor.Skalkin@...nsynergy.com>
Subject: Re: [PATCH v2 4/6] firmware: arm_scmi: add SCMIv3.0 Sensors
 timestamped reads

On 10.11.20 18:04, Cristian Marussi wrote:
> Hi Peter
> 
> thanks for the review.
> 
> On Tue, Nov 10, 2020 at 05:01:26PM +0100, Peter Hilber wrote:
>> On 26.10.20 21:10, Cristian Marussi wrote:
>>> Add new .reading_get_timestamped() method to sensor_ops to support SCMIv3.0
>>> timestamped reads.
>>>
>>> Signed-off-by: Cristian Marussi <cristian.marussi@....com>
>>> ---
>>>  drivers/firmware/arm_scmi/sensors.c | 134 ++++++++++++++++++++++++++--
>>>  include/linux/scmi_protocol.h       |  22 +++++
>>>  2 files changed, 151 insertions(+), 5 deletions(-)
>>>
>>> diff --git a/drivers/firmware/arm_scmi/sensors.c b/drivers/firmware/arm_scmi/sensors.c
>>> index 5a18f8c84bef..bdb0ed0df683 100644
>>> --- a/drivers/firmware/arm_scmi/sensors.c
>>> +++ b/drivers/firmware/arm_scmi/sensors.c
>>> @@ -156,6 +156,27 @@ struct scmi_msg_sensor_reading_get {
>>>  #define SENSOR_READ_ASYNC  BIT(0)
>>>  };
>>>
>>> +struct scmi_resp_sensor_reading_get {
>>> +   __le64 readings;
>>> +};
>>> +
>>> +struct scmi_resp_sensor_reading_complete {
>>> +   __le32 id;
>>> +   __le64 readings;
>>> +};
>>
>> In my understanding the id field is not present in the spec. The
>> implementation seems to have introduced it already before this patch.
>>
> 
> Well, it is indeed defined in 4.7.3.1 "SENSOR_READING_COMPLETE" both in
> SCMI V3.0 and in V2.0: it is the async delayed response and this 'id'
> represents the sensor_id: in fact it is used only the in the async path
> in the reading funcs; the sync version uses directly sensor_reading_le.
> (which has no id n it)

You are right, sorry for the noise.

>>> +/**
>>> + * scmi_sensor_reading_get  - Read scalar sensor value
>>> + * @handle: Platform handle
>>> + * @sensor_id: Sensor ID
>>> + * @value: The 64bit value sensor reading
>>> + *
>>> + * This function returns a single 64 bit reading value representing the sensor
>>> + * value; if the platform SCMI Protocol implementation and the sensor support
>>> + * multiple axis and timestamped-reads, this just returns the first axis while
>>> + * dropping the timestamp value.
>>> + * Use instead the @scmi_sensor_reading_get_timestamped to retrieve the array of
>>> + * timestamped multi-axis values.
>>> + *
>>> + * Return: 0 on Success
>>> + */
>>>  static int scmi_sensor_reading_get(const struct scmi_handle *handle,
>>>                                u32 sensor_id, u64 *value)
>>>  {
>>> @@ -593,18 +629,105 @@ static int scmi_sensor_reading_get(const struct scmi_handle *handle,
>>
>> How about changing the scmi_xfer_get_init() rx_size to 0 (in the
>> immediately preceding, not shown lines)? An SCMI platform might not
>> expect to just have room for the first reading, excluding the timestamp.
>>
> 
> Ah right, because this is the old v2.0 interface which I kept unchanged but
> now internally the same v3.0 SENSOR_READING_GET message on a v3.0 platform
> could return multiple per-axis timestamped values even if I just return
> the first u64 without timestamp. Is this that you mean ?

Yes.

Best regards,

Peter