linux-kernel - Re: [PATCH 0/2] iio: frequency: add iio support for Amlogic clock measure

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Date: Tue, 25 Jun 2024 11:38:44 +0200
From: Neil Armstrong <neil.armstrong@...aro.org>
To: Jerome Brunet <jbrunet@...libre.com>, Jonathan Cameron
 <jic23@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>
Cc: Kevin Hilman <khilman@...libre.com>, linux-kernel@...r.kernel.org,
 linux-amlogic@...ts.infradead.org, linux-iio@...r.kernel.org,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>,
 linux-arm-msm <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH 0/2] iio: frequency: add iio support for Amlogic clock
 measure

Hi,

[+cc people from linux-msm]

On 24/06/2024 19:31, Jerome Brunet wrote:
> Add support for the HW found in most Amlogic SoC dedicated to measure
> system clocks.
> 
> This drivers aims to replace the one found in
> drivers/soc/amlogic/meson-clk-measure.c with following improvements:
> 
> * Access to the measurements through the IIO API:
>    Easier re-use of the results in userspace and other drivers
> * Controllable scale with raw measurements
> * Higher precision with processed measurements
> 
> Jerome Brunet (2):
>    dt-bindings: iio: frequency: add clock measure support
>    iio: frequency: add amlogic clock measure support
> 
>   .../iio/frequency/amlogic,clk-msr-io.yaml     |  50 ++
>   drivers/iio/frequency/Kconfig                 |  15 +
>   drivers/iio/frequency/Makefile                |   1 +
>   drivers/iio/frequency/amlogic-clk-msr-io.c    | 802 ++++++++++++++++++
>   4 files changed, 868 insertions(+)
>   create mode 100644 Documentation/devicetree/bindings/iio/frequency/amlogic,clk-msr-io.yaml
>   create mode 100644 drivers/iio/frequency/amlogic-clk-msr-io.c
> 

While I really appreciate the effort, and the code looks cool, the clkmsr is really
a debug tool, and I'm not sure IIO is the right place for such debug tool ?

There's almost the same interface on qcom SoCs (https://github.com/linux-msm/debugcc) but
they chose to keep it in userspace until we find an appropriate way to expose
this from the kernel the right way.

If it enabled us to monitor a frequency input for a product use-case, IIO would be
the appropriate interface, but AFAIK it's only internal clocks and thus I'm worried
it's not the best way to expose those clocks.

Neil