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

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Message-ID: <YiYYa7GkknJ+CAuL@kuha.fi.intel.com>
Date:   Mon, 7 Mar 2022 16:36:27 +0200
From:   Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:     Alvin Šipraga <alvin@...s.dk>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        �ipraga <alsi@...g-olufsen.dk>,
        linux-usb@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/4] usb: typec: add TUSB320xA driver

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?

thanks,

-- 
heikki