linux-kernel - Re: [PATCH v3 3/3] i2c: mpc: Use i2c-scl-clk-low-timeout-ms i2c property

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Date:   Tue, 14 Mar 2023 21:48:01 +0100
From:   Andi Shyti <andi.shyti@...nel.org>
To:     Chris Packham <Chris.Packham@...iedtelesis.co.nz>
Cc:     Andi Shyti <andi.shyti@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Wolfram Sang <wsa@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Ryan Chen <ryan_chen@...eedtech.com>
Subject: Re: [PATCH v3 3/3] i2c: mpc: Use i2c-scl-clk-low-timeout-ms i2c
 property

Hi Chris,

> >>> "fsl,timeout" is marked as deprecated and replaced by the
> >>> "i2c-scl-clk-low-timeout-ms" i2c property.
> >>>
> >>> Use this latter and, in case it is missing, for back
> >>> compatibility, check whether we still have "fsl,timeout" defined.
> >>>
> >>> Signed-off-by: Andi Shyti <andi.shyti@...nel.org>
> >>> Reviewed-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
> >>> ---
> >>>   drivers/i2c/busses/i2c-mpc.c | 12 +++++++++++-
> >>>   1 file changed, 11 insertions(+), 1 deletion(-)
> >>>
> >>> diff --git a/drivers/i2c/busses/i2c-mpc.c b/drivers/i2c/busses/i2c-mpc.c
> >>> index 87e5c1725750..28f11e30ac50 100644
> >>> --- a/drivers/i2c/busses/i2c-mpc.c
> >>> +++ b/drivers/i2c/busses/i2c-mpc.c
> >>> @@ -843,8 +843,18 @@ static int fsl_i2c_probe(struct platform_device *op)
> >>>   			mpc_i2c_setup_8xxx(op->dev.of_node, i2c, clock);
> >>>   	}
> >>>   
> >>> +	/*
> >>> +	 * "fsl,timeout" has been marked as deprecated and, to maintain
> >>> +	 * backward compatibility, we will only look for it if
> >>> +	 * "i2c-scl-clk-low-timeout-ms" is not present.
> >>> +	 */
> >>>   	result = of_property_read_u32(op->dev.of_node,
> >>> -				      "fsl,timeout", &mpc_ops.timeout);
> >>> +				      "i2c-scl-clk-low-timeout-ms",
> >>> +				      &mpc_ops.timeout);
> >>> +	if (result == -EINVAL)
> >>> +		result = of_property_read_u32(op->dev.of_node,
> >>> +					      "fsl,timeout", &mpc_ops.timeout);
> >> Wasn't old property in us and new one is in ms?
> > Thanks, Krzysztof! Good catch!
> >
> > Chris, you are the only user of this property, as of now. Is it
> > OK if we keep it ms? I will send a proper patch to do the
> > conversion.
> >
> > To me it doesn't make much sense to have the timeout defined in
> > us as that's of the same order of the raising and falling time
> > of the clock. Any opinion?

> I think it'd be easier to stick to us as then the same code can be used 
> to probe both the old property and the new one. However I won't object 
> if you adjust for the us to ms conversion between handling the new 
> property vs the old one.

yeah... indeed it became quite ugly.

OK, I will just rename it from "i2c-scl-clk-low-timeout-ms" to
"i2c-scl-clk-low-timeout-us", respin the schema pull request and
leave everything as it is.

Thanks for your input, Chris!

Andi