linux-kernel - Re: [PATCH v2 2/5] dt-bindings: rtc: qcom-pm8xxx: document no-alarm flag

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Message-ID: <a91e4a52-c427-bfdb-0675-f8417dc24006@marek.ca>
Date: Mon, 14 Oct 2024 10:09:48 -0400
From: Jonathan Marek <jonathan@...ek.ca>
To: Krzysztof Kozlowski <krzk@...nel.org>
Cc: linux-arm-msm@...r.kernel.org,
 Alexandre Belloni <alexandre.belloni@...tlin.com>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Satya Priya <quic_c_skakit@...cinc.com>,
 "open list:REAL TIME CLOCK (RTC) SUBSYSTEM" <linux-rtc@...r.kernel.org>,
 "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
 <devicetree@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/5] dt-bindings: rtc: qcom-pm8xxx: document no-alarm
 flag

On 10/14/24 9:38 AM, Krzysztof Kozlowski wrote:
> On 14/10/2024 14:58, Jonathan Marek wrote:
>> On 10/14/24 3:34 AM, Krzysztof Kozlowski wrote:
>>> On Sun, Oct 13, 2024 at 01:15:27AM -0400, Jonathan Marek wrote:
>>>> Qualcomm x1e80100 firmware sets the ownership of the RTC alarm to ADSP.
>>>> Thus writing to RTC alarm registers and receiving alarm interrupts is not
>>>> possible.
>>>>
>>>> Add a no-alarm flag to support RTC on this platform.
>>>>
>>>> Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
>>>> ---
>>>>    Documentation/devicetree/bindings/rtc/qcom-pm8xxx-rtc.yaml | 5 +++++
>>>>    1 file changed, 5 insertions(+)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/rtc/qcom-pm8xxx-rtc.yaml b/Documentation/devicetree/bindings/rtc/qcom-pm8xxx-rtc.yaml
>>>> index d274bb7a534b5..210f76a819e90 100644
>>>> --- a/Documentation/devicetree/bindings/rtc/qcom-pm8xxx-rtc.yaml
>>>> +++ b/Documentation/devicetree/bindings/rtc/qcom-pm8xxx-rtc.yaml
>>>> @@ -40,6 +40,11 @@ properties:
>>>>        description:
>>>>          Indicates that the setting of RTC time is allowed by the host CPU.
>>>>    
>>>> +  no-alarm:
>>>> +    $ref: /schemas/types.yaml#/definitions/flag
>>>> +    description:
>>>> +      Indicates that RTC alarm is not owned by HLOS (Linux).
>>>
>>> This is not even properly used/tested, because you disable the RTC
>>> entirely in your DTS.
>>>
>>
>> What? The next patch in this series is enabling RTC on x1e using this flag
> 
> D'oh, right, I must have looked at wrong diff hunks. I had somehow
> impression you add status=reserved, but you just dropped it.
> 
>>
>>> I expect here unified property for all Qualcomm devices for this case.
>>> We already have "remotely-controlled" and other flavors. I don't want
>>> each device to express the same with different name...
>>>
>>> Also: missing vendor prefix.
>>>
>>
>> I don't care what the property is named (as long as its a bool
>> property), if you have a name you prefer I will use it.
>>
>> The existing 'allow-set-time' property (also related to HLOS permissions
>> to the RTC) is also specific to this driver doesn't have a vendor prefix.
> 
> Yeah, that one sneaked in some years ago.
> 
> So you can set time, but not alarm? Some previous platforms could not
> set time, but could set alarm?
> 
> I wonder whether we actually describe the real issue here. It looks like
> group of band-aids.
> 
> Best regards,
> Krzysztof
> 

Firmware can set different permissions for the RTC time (0x61xx) and RTC 
alarm (0x62xx) regions. So it makes sense to have one flag for each region.

RTC time is almost always read-only (not owned by HLOS/Linux), so the 
'allow-set-time' property is almost never used (the driver supports 
using nvmem to store an offset for setting time as a workaround).

The "can set time, but not alarm" combination will probably never be 
used, but the 3 other combinations are possible (the common one is 
"can't set time, but can set alarm").

(in the next patch I deleted the "alarm" region/interrupt from the dts 
but that's wrong, the HW still exists, the patch should be only 
replacing the reserved status with the new flag)