linux-kernel - Re: [PATCH 3/4] arm64: dts: qcom: qcm6490-fairphone-fp5: Enable CCI pull-up

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Message-Id: <DD7V3G4RLB2I.QYT4BWT1LA5U@fairphone.com>
Date: Thu, 02 Oct 2025 15:14:13 +0200
From: "Luca Weiss" <luca.weiss@...rphone.com>
To: "Konrad Dybcio" <konrad.dybcio@....qualcomm.com>, "Griffin
 Kroah-Hartman" <griffin.kroah@...rphone.com>, "Mauro Carvalho Chehab"
 <mchehab@...nel.org>, "Rob Herring" <robh@...nel.org>, "Krzysztof
 Kozlowski" <krzk+dt@...nel.org>, "Conor Dooley" <conor+dt@...nel.org>,
 <devicetree@...r.kernel.org>, "Daniel Scally" <djrscally@...il.com>,
 "Sakari Ailus" <sakari.ailus@...ux.intel.com>, "Bjorn Andersson"
 <andersson@...nel.org>, "Konrad Dybcio" <konradybcio@...nel.org>,
 André Apitzsch <git@...tzsch.eu>, "Bryan O'Donoghue"
 <bryan.odonoghue@...aro.org>, "Wolfram Sang" <wsa@...nel.org>
Cc: <linux-media@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
 <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH 3/4] arm64: dts: qcom: qcm6490-fairphone-fp5: Enable CCI
 pull-up

Hi Konrad,

Answering on behalf of Griffin :)

On Thu Oct 2, 2025 at 2:45 PM CEST, Konrad Dybcio wrote:
> On 10/2/25 12:15 PM, Griffin Kroah-Hartman wrote:
>> Enable vreg_l6p which is used as a pull-up for the CCI busses, to make
>> sure I2C communication works as expected.
>> 
>> Signed-off-by: Griffin Kroah-Hartman <griffin.kroah@...rphone.com>
>> ---
>
> Makes me wonder if we should maybe extend the CCI definition
> (or maybe the common i2c-bus binding?) to accept an external
> pull-up supply, as this is a common problem.. (+Bryan, Wolfram)

Yes!

Unfortunately though this effort has stalled some years ago. There is
"struct regulator *bus_regulator;" in "struct i2c_adapter" already and
vbus-supply is documented in i2c-mt65xx but afaik this not functional
because some code was ripped out ago because of some AMDGPU regressions.

> We could then shut down the regulator when cameras are not
> in use, preserving some trace amounts of power.
>
> Or maybe L6P is already used as a pull-up supply for more things
> onboard and should be always-on either way? Could you please
> check that, Griffin?

L6P is only used as pull-up reg for cci0, cci1 and cci3; and as power
for stuff in the camera modules. So if everything camera-related is off,
turning it off is actually a good idea.

Regards
Luca

>
> Konrad
>
>>  arch/arm64/boot/dts/qcom/qcm6490-fairphone-fp5.dts | 2 ++
>>  1 file changed, 2 insertions(+)
>> 
>> diff --git a/arch/arm64/boot/dts/qcom/qcm6490-fairphone-fp5.dts b/arch/arm64/boot/dts/qcom/qcm6490-fairphone-fp5.dts
>> index e115b6a52b299ef663ccfb614785f8f89091f39d..2dd2c452592aa6b0ac826f19eb9cb1a8b90cee47 100644
>> --- a/arch/arm64/boot/dts/qcom/qcm6490-fairphone-fp5.dts
>> +++ b/arch/arm64/boot/dts/qcom/qcm6490-fairphone-fp5.dts
>> @@ -749,6 +749,8 @@ vreg_l6p: ldo6 {
>>  				regulator-name = "vreg_l6p";
>>  				regulator-min-microvolt = <1700000>;
>>  				regulator-max-microvolt = <1904000>;
>> +				/* Pull-up for CCI I2C busses */
>> +				regulator-always-on;
>>  			};
>>  
>>  			vreg_l7p: ldo7 {
>>