linux-kernel - Re: [RFC PATCH v2] driver core: add a debugfs entry to show deferred devices

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Date:   Tue, 19 Jun 2018 22:54:45 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Mark Brown <broonie@...nel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        linux-arm Mailing List <linux-arm-kernel@...ts.infradead.org>,
        Rob Herring <robh@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [RFC PATCH v2] driver core: add a debugfs entry to show deferred
 devices

Hello Andy,

Thanks a lot for your feedback.

On 06/19/2018 09:55 PM, Andy Shevchenko wrote:
> On Tue, Jun 19, 2018 at 10:53 PM, Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
>> On Tue, Jun 19, 2018 at 9:33 PM, Javier Martinez Canillas
>> <javierm@...hat.com> wrote:
>>> For debugging purposes it may be useful to know what are the devices whose
>>> probe function was deferred. Add a debugfs entry showing that information.
> 
>>> +static int deferred_devs_open(struct inode *inode, struct file *file)
>>> +{
>>> +       return single_open(file, deferred_devs_show, inode->i_private);
>>> +}
>>> +
>>> +static const struct file_operations deferred_devs_fops = {
>>> +       .owner = THIS_MODULE,
>>> +       .open = deferred_devs_open,
>>> +       .read = seq_read,
>>> +       .llseek = seq_lseek,
>>> +       .release = single_release,
>>> +};
>>
>> Isn't this DEFINE_SHOW_ATTRIBUTE() ?
>

Indeed.
 
> Besides that, you are summoning Greg's dark side :-)
> See below.
> 
>>> +       if (IS_ENABLED(CONFIG_DEBUG_FS)) {
>>> +               deferred_devices = debugfs_create_file("deferred_devices",
>>> +                                                      0444, NULL, NULL,
>>> +                                                      &deferred_devs_fops);
> 
>>> +               if (!deferred_devices)
>>> +                       return -ENOMEM;
> 
> This must not prevent the execution. So, the check introduces actually
> a regression.
>

Fair enough, I'll fix these an re-spin the patch.
 
>>> +       }
> 

Best regards,
-- 
Javier Martinez Canillas
Software Engineer - Desktop Hardware Enablement
Red Hat