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

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Message-ID: <96091daa-0868-45c8-b16b-39076862b8ee@kernel.org>
Date: Thu, 2 Oct 2025 14:12:13 +0100
From: Bryan O'Donoghue <bod@...nel.org>
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

On 02/10/2025 13:45, 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.

"vreg_l6p is the voltage source for the pull-up resistor"

>>
>> 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)


always-on is up to the platform - i.e. do you care about the 
floating-state of the i2c bus in power-collapse anyway ? Feels like 
something up to the platform designers.
> 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?

If we drop always-on and introduce a "pullup-supply" to the CCI bindings 
then, it would be up the CCI driver to enable/disable the bus pullups 
and then we can optionally do the power-rail disable when entering 
power-collapse.

That'd be nice.

As-is though I personally am fine with the patch as-is with the updated 
commit text above - consider the CCI change as extra homework ;)

Assuming the commit log is tweaked.

Reviewed-by: Bryan O'Donoghue <bod@...nel.org>