linux-kernel - Re: [PATCH V1 4/4] phy: qcom-qmp-ufs: read max-microamp values from device tree

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Message-ID: <2dc54d35-4811-4153-bd36-843a374d9c4f@quicinc.com>
Date: Thu, 14 Aug 2025 02:31:21 +0530
From: Nitin Rawat <quic_nitirawa@...cinc.com>
To: Bjorn Andersson <andersson@...nel.org>, Mark Brown <broonie@...nel.org>
CC: Konrad Dybcio <konrad.dybcio@....qualcomm.com>, <vkoul@...nel.org>,
        <kishon@...nel.org>, <mani@...nel.org>, <conor+dt@...nel.org>,
        <bvanassche@....org>, <neil.armstrong@...aro.org>,
        <dmitry.baryshkov@....qualcomm.com>, <konradybcio@...nel.org>,
        <krzk+dt@...nel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-phy@...ts.infradead.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>
Subject: Re: [PATCH V1 4/4] phy: qcom-qmp-ufs: read max-microamp values from
 device tree



On 8/12/2025 1:18 AM, Nitin Rawat wrote:
> 
> 
> On 8/11/2025 9:20 PM, Bjorn Andersson wrote:
>> On Thu, Aug 07, 2025 at 08:09:56PM +0100, Mark Brown wrote:
>>> On Thu, Aug 07, 2025 at 07:43:15PM +0200, Konrad Dybcio wrote:
>>>> On 8/7/25 7:26 PM, Mark Brown wrote:
>>>
>>>>> Note that that's specifying OPPs which is different...
>>>
>>>> The microamp properties are in the top-level, not under OPP if
>>>> that's what you meant
>>>
>>> I mean the OPPs use case is an existing well known one for dumping stuff
>>> into DT.
>>>
>>>>> That doesn't mean that it's a good idea to put that information in the
>>>>> DT, nor if it is sensible to put in DT does it mean that it's a good
>>>>> idea to define a generic property that applies to all regulator
>>>>> consumers which is what I now think Konrad is proposing.
>>>
>>>> Yeah, that's what I had in mind
>>>
>>>> I was never able to get a reliable source for those numbers myselfe
>>>> either.. At least some of them are prooooobably? chosen based on the
>>>> used regulator type, to ensure it's always in HPM..
>>>
>>> That's what set_mode() is for.  Like I say it's becoming less and less
>>> relevant though.
>>>
>>
>> set_mode() just applies the mode to the regulator_dev, so in cases where
>> you have multiple consumers of a regulator_dev things would break.
>>
>> Further, there are numerous cases where we have multiple consumers each
>> needing a "low" mode, but their combined load requires a "high" mode.
>>
>> set_load() and its aggregation of the inputs deals with both of these
>> issues.
>>
>>
>> Whether mode setting is becoming less relevant in our hardware, that I
>> don't have the definitive answer to.
>>
>>>> That said, our drivers cover a wide variety of hardware, built on a
>>>> wide variety of process nodes, with different configurations, etc.,
>>>> so it's either polluting the DT, or polluting the driver with
>>>> per-compatible hardcoded data (and additional compatibles because
>>>> fallbacks wouldn't work most of the time)
>>
>> If this is our reason for putting it in DeviceTree, then we should write
>> that in the commit message :)
>>
>>>
>>> That's really not a persuasive argument for adding a genric property
>>> that applies to all regulator consumers...
>>>
>>
>> I agree, even if we determine that this belongs in DT, because it needs
>> to be tweaked on a per-board basis, it's still only applicable to a
>> fraction of our device nodes.
> 
> Hi Bjorn & Mark,
> 
> I had a follow-up discussion with the PHY designer to confirm whether 
> this value could vary at the board level. Based on their response, it's 
> a fixed value for the SoC and remains consistent across different 
> boards. Therefore, I'm comfortable removing it from the device tree and 
> using hardcoded, per-compatible data in the driver.
> 
> The only concern is that this approach may lead to driver bloat over 
> time, as more SoCs are added and each requires its own hardcoded 
> configuration.
> 
> Regards,
> Nitin
> 
> 
Based on the current understanding, I plan to post a revised patch that 
uses hardcoded, per-compatible data within the driver, rather than 
specifying it in the device tree. Please let me know if anyone has any 
concerns with this approach.

Thanks,
Nitin


> 
> 
> 
> 
>>
>> Regards,
>> Bjorn
>>
>>> My instinct with this stuff is generally to avoid putting it in the DT,
>>> we see far too many instances where someone's typed some numbers in
>>> wrongly or discovers the ability to drive the hardware harder and needs
>>> to tune the numbers - once something is ABI you're stuck just trusting
>>> the numbers.  That said I'm not going to stop you putting something
>>> specific to this driver in there, I just don't think this is a good idea
>>> as a generic property.
>>
>