linux-kernel - Re: [PATCH v6] mfd: syscon: Add hardware spinlock support

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Date:   Mon, 18 Dec 2017 14:54:13 +0800
From:   Baolin Wang <baolin.wang@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Lee Jones <lee.jones@...aro.org>, Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mark Brown <broonie@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>
Subject: Re: [PATCH v6] mfd: syscon: Add hardware spinlock support

On 15 December 2017 at 21:13, Arnd Bergmann <arnd@...db.de> wrote:
> On Fri, Dec 15, 2017 at 11:42 AM, Lee Jones <lee.jones@...aro.org> wrote:
>
>>> @@ -87,6 +88,30 @@ static struct syscon *of_syscon_register(struct device_node *np)
>>>       if (ret)
>>>               reg_io_width = 4;
>>>
>>> +     ret = of_hwspin_lock_get_id(np, 0);
>>> +     if (ret > 0) {
>>> +             syscon_config.hwlock_id = ret;
>>> +             syscon_config.hwlock_mode = HWLOCK_IRQSTATE;
>>> +     } else {
>>> +             switch (ret) {
>>> +             case -ENOENT:
>>> +                     /* Ignore missing hwlock, it's optional. */
>>> +                     break;
>>> +             case 0:
>>> +                     /* In case of the HWSPINLOCK is not enabled. */
>>> +                     if (!IS_ENABLED(CONFIG_HWSPINLOCK))
>>> +                             break;
>>> +
>>> +                     ret = -EINVAL;
>>> +                     /* fall-through */
>>> +             default:
>>> +                     pr_err("Failed to retrieve valid hwlock: %d\n", ret);
>>> +                     /* fall-through */
>>> +             case -EPROBE_DEFER:
>>> +                     goto err_regmap;
>>> +             }
>
> The 'case 0' seems odd here, are we sure that this is always a failure?
> From the of_hwspin_lock_get_id() definition it looks like zero might
> be valid, and the !CONFIG_HWSPINLOCK implementation appears
> to be written so that we should consider '0' valid but unused and
> silently continue with that. If that is generally not the intended
> use, it should probably return -EINVAL or something like that.

Yes, 0 is valid for of_hwspin_lock_get_id(), but if we pass 'hwlock id
= 0' to regmap, the regmap core will not regard it as a valid hwlock
id to request the hwlock and will use default mutex lock instead of
hwlock, which will cause problems. Meanwhile if we silently continue
with case 0, users will not realize that they set one invalid hwlock
id to regmap core, so here we regarded case 0 as one invalid id to
print error messages for users.

-- 
Baolin.wang
Best Regards