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

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Date:   Tue, 30 Jun 2020 11:59:54 +0300
From:   Grygorii Strashko <grygorii.strashko@...com>
To:     Andrzej Hajda <a.hajda@...sung.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

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?


-- 
Best regards,
grygorii