linux-kernel - Re: [PATCH v6 2/4] driver core: add deferring probe reason to devices

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Date:   Tue, 30 Jun 2020 17:41:26 +0200
From:   Andrzej Hajda <a.hajda@...sung.com>
To:     Grygorii Strashko <grygorii.strashko@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Jernej Skrabec <jernej.skrabec@...l.net>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Jonas Karlman <jonas@...boo.se>, linux-kernel@...r.kernel.org,
        "open list:DRM DRIVERS" <dri-devel@...ts.freedesktop.org>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Neil Armstrong <narmstrong@...libre.com>,
        andy.shevchenko@...il.com, Mark Brown <broonie@...nel.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH v6 2/4] driver core: add deferring probe reason to
 devices_deferred property


On 30.06.2020 10:59, Grygorii Strashko wrote:
> Hi
>
> On 29/06/2020 14:28, Andrzej Hajda wrote:
>> Hi Grygorii,
>>
>> (...)
>>
>>>>    /*
>>>>     * deferred_devs_show() - Show the devices in the deferred probe
>>>> pending list.
>>>>     */
>>>> @@ -221,7 +241,8 @@ static int deferred_devs_show(struct seq_file *s,
>>>> void *data)
>>>>        mutex_lock(&deferred_probe_mutex);
>>>>          list_for_each_entry(curr, &deferred_probe_pending_list,
>>>> deferred_probe)
>>>> -        seq_printf(s, "%s\n", dev_name(curr->device));
>>>> +        seq_printf(s, "%s\t%s", dev_name(curr->device),
>>>> + curr->device->p->deferred_probe_reason ?: "\n");
>>>>          mutex_unlock(&deferred_probe_mutex);
>>>>
>>>
>>> Sry, may be i missing smth, but shouldn't it be optional
>>> (CONFIG_DEBUG_FS is probably too generic).
>>>
>>
>> I am not sure what exactly are you referring to, but this patch does not
>> add new property, it just extends functionality of existing one.
>
> Sry, needed to be more specific.
>
> You've added  device_set_deferred_probe_reson(dev, &vaf);
> which expected to be used on every EPROBE_DEFER in dev_err_probe() in 
> combination with
>
> +       } else {
> +               device_set_deferred_probe_reson(dev, &vaf);
>                 dev_dbg(dev, "error %d: %pV", err, &vaf);
>
> ^^ dev_dbg() does not add any runtime overhead during boot unless enabled
> +       }
>
> But:
>
> +void device_set_deferred_probe_reson(const struct device *dev, struct 
> va_format *vaf)
> +{
> +       const char *drv = dev_driver_string(dev);
> +
> +       mutex_lock(&deferred_probe_mutex);
> +
> +       kfree(dev->p->deferred_probe_reason);
> +       dev->p->deferred_probe_reason = kasprintf(GFP_KERNEL, "%s: 
> %pV", drv, vaf);
> +
> +       mutex_unlock(&deferred_probe_mutex);
> +}
>
> ^^ Adds locking, kfree() and kasprintf() for every deferred probe 
> during boot and can't be disabled.
>
> Right?


Right, but usually the burden should be insignificant in comparison to 
probe time, so I do not think it is worth optimizing.


Regards

Andrzej


>
>