linux-kernel - Re: [PATCH 2/7] i2c: qcom-cci: Add msm8953 compatible

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Message-ID: <72a24049-81e4-4ce9-8bdf-63315209be7a@oss.qualcomm.com>
Date: Thu, 4 Sep 2025 13:51:27 +0200
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Luca Weiss <luca@...aweiss.eu>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>
Cc: Loic Poulain <loic.poulain@....qualcomm.com>,
        Robert Foss <rfoss@...nel.org>, Andi Shyti <andi.shyti@...nel.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        ~postmarketos/upstreaming@...ts.sr.ht, phone-devel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, linux-i2c@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] i2c: qcom-cci: Add msm8953 compatible

On 8/15/25 9:12 AM, Luca Weiss wrote:
> Hi Wolfram,
> 
> On 2025-08-11 14:13, Wolfram Sang wrote:
>> On Sun, Aug 10, 2025 at 05:37:53PM +0200, Luca Weiss wrote:
>>> Add a config for the v1.2.5 CCI found on msm8953 which has different
>>
>> Given the above version number...
>>
>>>  static const struct of_device_id cci_dt_match[] = {
>>>      { .compatible = "qcom,msm8226-cci", .data = &cci_v1_data},
>>> +    { .compatible = "qcom,msm8953-cci", .data = &cci_msm8953_data},
>>
>> ... why don't we use it here to stay consistent? cci_v1_2_5_data?
> 
> I don't think the existing 'v2' or 'v1' configs have much to do with the actual
> HW_VERSION of the IP block. For example on of the newer Qualcomm SoCs has HW
> version 1.7.0 and is many years newer than the msm8996 which was called 'v2'.

Most of the i2c-speed-dependent configs are electrical and therefore may
be configured as you wish.. I recall Sony Xperia kernels made changes to
that rather often, whether really necessary - I don't know.
The programming guide suggests a couple sets of values, picked in order
to meet the I2C spec.

The queue depths and max r/w lengths are per-instance (SoC specific) and
change very rarely.

> 
> I'm also not sure what these parameters depend on, if it's CCI HW version, or
> something else. So naming it after the SoC should be a safer bet. Also the
> msm8974-cci was only named 'v1.5' because it's an inbetween mix of the v1 and
> v2 that were already upstream so arguably that one shouldn't have been called
> v1.5 in the first place either.

AFAICS there is no "v2" CCI in existence, msm8996 is v1.4.0 and newer
platforms are v1.x.y.

JFYI there's a revision ID register at (base + 0x0) which the driver's probe
function conveniently reads and prints with dev_dbg.

Konrad