linux-kernel - Re: [PATCH 1/4] arm64: dts: qcom: sc8280xp: rename i2c5 to i2c21

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Message-ID: <Y5ilMI1QYsx1uaNe@hovoldconsulting.com>
Date:   Tue, 13 Dec 2022 17:15:44 +0100
From:   Johan Hovold <johan@...nel.org>
To:     Konrad Dybcio <konrad.dybcio@...aro.org>
Cc:     Shazad Hussain <quic_shazhuss@...cinc.com>,
        Brian Masney <bmasney@...hat.com>, andersson@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, robh+dt@...nel.org,
        johan+linaro@...nel.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        ahalaney@...hat.com, echanude@...hat.com
Subject: Re: [PATCH 1/4] arm64: dts: qcom: sc8280xp: rename i2c5 to i2c21

On Tue, Dec 13, 2022 at 04:44:15PM +0100, Konrad Dybcio wrote:
> 
> 
> On 13.12.2022 16:42, Johan Hovold wrote:
> > On Tue, Dec 13, 2022 at 04:39:54PM +0100, Johan Hovold wrote:
> >> On Tue, Dec 13, 2022 at 09:04:39PM +0530, Shazad Hussain wrote:
> >>> On 12/13/2022 8:58 PM, Johan Hovold wrote:
> > 
> >>>>> So qup2_i2c18 becomes qup2_i2c2. Would I use the flat naming scheme for
> >>>>> the alias like so?
> >>>>>
> >>>>>      aliases {
> >>>>>          i2c18 = &qup2_i2c2;
> >>>>>      }
> >>>>
> >>>> Or perhaps the i2c controllers should use a zero-based index instead of
> >>>> being named after the serial engines (e.g. as we do for the console
> >>>> uart).
> >>>>
> >>>> How are they named in the schematics?
> >>>
> >>> We should use from 0 to N.
> >>
> >> With N being 23 after the number of serial engines, or the number of
> >> available i2c buses on a particular board minus one?
> > 
> > Looks like the more recent Qualcomm platforms use aliases that reflect
> > the engine number (i.e. 0 to 23) for i2c and spi.
> IMO it makes the most sense, as it tells the userspace "hello, this
> device is connected to the physical I2Cn on the SoC" as opposed to
> "hello, this device is connected to the nth enabled bus on this
> particular board".

But I guess it still depends on the board. I wouldn't expect a product
with four serial ports to use the engine numbers on labels for the
connectors for example.

Johan