linux-kernel - Re: [PATCH 3/4] usb: typec: add TUSB320xA driver

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Message-ID: <871qzcd3tw.fsf@bang-olufsen.dk>
Date:   Tue, 8 Mar 2022 12:30:19 +0000
From:   Alvin Šipraga <ALSI@...g-olufsen.dk>
To:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>
CC:     Alvin Šipraga <alvin@...s.dk>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/4] usb: typec: add TUSB320xA driver

Heikki Krogerus <heikki.krogerus@...ux.intel.com> writes:

> On Mon, Mar 07, 2022 at 10:17:04PM +0000, Alvin Šipraga wrote:
>> Hi Heikki,
>> 
>> Heikki Krogerus <heikki.krogerus@...ux.intel.com> writes:
>> 
>> > Hi,
>> >
>> > On Tue, Mar 01, 2022 at 02:20:07PM +0100, Alvin Šipraga wrote:
>> >> From: Alvin Šipraga <alsi@...g-olufsen.dk>
>> >> 
>> >> The TUSB320LA and TUSB320HA (or LAI, HAI) chips are I2C controlled
>> >> non-PD Type-C port controllers. They support detection of cable
>> >> orientation, port attachment state, and role, including Audio Accessory
>> >> and Debug Accessory modes. Add a typec class driver for this family.
>> >> 
>> >> Note that there already exists an extcon driver for the TUSB320 (a
>> >> slightly older revision that does not support setting role preference or
>> >> disabling the CC state machine). This driver is loosely based on that
>> >> one.
>> >
>> > This looked mostly OK to me. There is one question below.
>> >
>> > <snip>
>> >
>> >> +static int tusb320xa_check_signature(struct tusb320xa *tusb)
>> >> +{
>> >> +	static const char sig[] = { '\0', 'T', 'U', 'S', 'B', '3', '2', '0' };
>> >> +	unsigned int val;
>> >> +	int i, ret;
>> >> +
>> >> +	mutex_lock(&tusb->lock);
>> >> +
>> >> +	for (i = 0; i < sizeof(sig); i++) {
>> >> +		ret = regmap_read(tusb->regmap, sizeof(sig) - 1 - i, &val);
>> >> +		if (ret)
>> >> +			goto done;
>> >> +
>> >> +		if (val != sig[i]) {
>> >> +			dev_err(tusb->dev, "signature mismatch!\n");
>> >> +			ret = -ENODEV;
>> >> +			goto done;
>> >> +		}
>> >> +	}
>> >> +
>> >> +done:
>> >> +	mutex_unlock(&tusb->lock);
>> >> +
>> >> +	return ret;
>> >> +}
>> >
>> > Couldn't that be done with a single read?
>> >
>> >         char sig[8];
>> >         u64 val;
>> >
>> >         strcpy(sig, "TUSB320")
>> >
>> >         mutex_lock(&tusb->lock);
>> >
>> >         ret = regmap_raw_read(tusb->regmap, 0, &val, sizeof(val));
>> >         ...
>> >         if (val != cpu_to_le64(*(u64 *)sig)) {
>> >         ...
>> >
>> > Something like that?
>> 
>> I think it's a bit cryptic - are you sure it's worth it just to save 8
>> one-off regmap_read()s? I could also just remove this check... I see it
>> mostly as a courtesy to the user in case the I2C address in his device
>> tree mistakenly points to some other unsuspecting chip.
>> 
>> BTW, do you have any feedback on the device tree bindings of this
>> series? Rob had some questions and I am not sure that my proposed
>> bindings are fully aligned with the typec subsystem expectations. Any
>> feedback would be welcome.
>
> I don't think I understand DT well enough to comment. I'm not
> completely sure what he's asking..

OK, no problem! Thanks for your reply.

Kind regards,
Alvin

>
>> I will wait for more comments and send a v2 in ~a week.
>
> thanks,