netdev - Re: [PATCH v1 4/7] usbnet: cdc_mbim: don't recover device if suspend fails in system sleep

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Message-ID: <CACVXFVMS4JNphgcU4oy7VQ1S6AoXQUcpRT2ODE_DP79AsnAY4g@mail.gmail.com>
Date:	Wed, 6 Mar 2013 21:48:19 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Bjørn Mork <bjorn@...k.no>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Jiri Kosina <jkosina@...e.cz>,
	Alan Stern <stern@...land.harvard.edu>,
	Oliver Neukum <oneukum@...e.de>, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org, linux-input@...r.kernel.org
Subject: Re: [PATCH v1 4/7] usbnet: cdc_mbim: don't recover device if suspend
 fails in system sleep

On Wed, Mar 6, 2013 at 8:04 PM, Bjørn Mork <bjorn@...k.no> wrote:
> Ming Lei <ming.lei@...onical.com> writes:
>
>> If suspend callback fails in system sleep context, usb core will
>> ignore the failure and let system sleep go ahead further, so
>> this patch doesn't recover device under this situation.
>>
>> Cc: Bjørn Mork <bjorn@...k.no>
>> Signed-off-by: Ming Lei <ming.lei@...onical.com>
>> ---
>>  drivers/net/usb/cdc_mbim.c |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/net/usb/cdc_mbim.c b/drivers/net/usb/cdc_mbim.c
>> index 248d2dc..ec58c2c 100644
>> --- a/drivers/net/usb/cdc_mbim.c
>> +++ b/drivers/net/usb/cdc_mbim.c
>> @@ -338,7 +338,7 @@ static int cdc_mbim_suspend(struct usb_interface *intf, pm_message_t message)
>>
>>       if (intf == ctx->control && info->subdriver && info->subdriver->suspend)
>>               ret = info->subdriver->suspend(intf, message);
>> -     if (ret < 0)
>> +     if (ret < 0 && PMSG_IS_AUTO(message))
>>               usbnet_resume(intf);
>>
>>  error:
>
> This condition will never happen because the subdriver callback always
> return 0 if !PMSG_IS_AUTO(message), so adding anything here is purely
> for documentation purposes.  That is OK for me.  But I do not see any
> point adding incomplete or wrong documentation.
>
> The above is incomplete because it ignores the failure and still return
> an error. And it is wrong because we ignore an error we cannot possibly
> handle in resume.  Only the subdriver can do that, which is why we must
> delegate this to the subdriver.
>
> I believe the correct here is to document the fact that we require the
> subdriver->suspend() callback to always return 0 if !PMSG_IS_AUTO(message).
> That is best done with a comment. No need to add any redundant code.

Considered that the subdriver might change its return value in future, how about
just add the below comment?

        /* TODO: resume() might need to handle suspend failure from subdriver */


Thanks,
--
Ming Lei
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