linux-kernel - Re: [PATCH 04/10] mmc: Add invert flag for clock phase signedness

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Message-Id: <c79e93c3-1678-412f-87c5-2b757d806574@www.fastmail.com>
Date:   Mon, 08 Nov 2021 10:51:48 +1030
From:   "Andrew Jeffery" <andrew@...id.au>
To:     "Chin-Ting Kuo" <chin-ting_kuo@...eedtech.com>,
        "Rob Herring" <robh+dt@...nel.org>,
        "Joel Stanley" <joel@....id.au>,
        "Ulf Hansson" <ulf.hansson@...aro.org>
Cc:     BMC-SW <BMC-SW@...eedtech.com>,
        "Steven Lee" <steven_lee@...eedtech.com>,
        "Michael Turquette" <mturquette@...libre.com>,
        "Stephen Boyd" <sboyd@...nel.org>,
        "Adrian Hunter" <adrian.hunter@...el.com>,
        "linux-aspeed@...ts.ozlabs.org" <linux-aspeed@...ts.ozlabs.org>,
        "openbmc@...ts.ozlabs.org" <openbmc@...ts.ozlabs.org>,
        linux-mmc <linux-mmc@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>
Subject: Re: [PATCH 04/10] mmc: Add invert flag for clock phase signedness

On Sat, 6 Nov 2021, at 20:32, Chin-Ting Kuo wrote:
> Hi Andrew,
>>> > -	rc = device_property_read_u32_array(dev, prop, degrees, 2);
>> > +	rc = device_property_read_u32_array(dev, prop, degrees, 4);
>> >  	phase->valid = !rc;
>> >  	if (phase->valid) {
>> > -		phase->in_deg = degrees[0];
>> > -		phase->out_deg = degrees[1];
>> > +		phase->inv_in_deg = degrees[0] ? true : false;
>> > +		phase->in_deg = degrees[1];
>> > +		phase->inv_out_deg = degrees[2] ? true : false;
>> > +		phase->out_deg = degrees[3];
>> 
>> This fundamentally breaks any in-tree users. We can't do this.
>> 
>> In terms of the binding, if negative phase values are something we must do,
>> we can just extend the value range to include [-359, -1] right?
>
> Yes, agree it and I tried it before. But, it seems that the device tree 
> doesn't support
> negative value with "-" prefixed and there is no device tree related 
> API used to get
> the negative value from .dts. Thus, I tried to add an additional flag 
> to present
> negative value.
>

Hmm. Still, I don't think we can break the binding this way.

Rob, Ulf, Adrian: What are your thoughts on handling phase offsets in 
[-360, 360] in the binding? Do we append the flag field? Add a separate 
property? I don't think interleaving the flags is desirable, though 
interested in your thoughts.

Andrew