linux-kernel - Re: [PATCH V3 0/3] cdc-acm: fix incorrect runtime wakeup in acm_tty

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Date:	Wed, 27 May 2015 13:56:18 +0800
From:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
To:	linux-kernel@...r.kernel.org, xinhuix.pan@...el.com,
	jin.can.zhuang@...el.com, gregkh@...uxfoundation.org,
	alan@...ux.intel.com
Subject: Re: [PATCH V3 0/3] cdc-acm: fix incorrect runtime wakeup in acm_tty_write

On 2015/5/27 12:13, Zhang, Yanmin wrote:
> Resend as V1/V2 have email format issue. Sorry for bothering.

Greg,

We have to abandon this patchset. Zhuang Jin Can, a USB expert,
reviewed the patches. He says acm_tty_write already considers
it carefully.

acm_tty_write puts the urb to a delayed queue when acm->susp_count
is not 0. acm_suspend adds 1 to acm->susp_count and acm_resume
decreases 1 from it .

Sorry for the bothering. Also thank Jin Can for the comments.

Yanmin

>
> I use Thunderbird. It has no a button to enable LKML email simply. :)
>
> V3: Change email config to resend.
> 	Add a space in comment.
>
>  ---
>
> There is a scenario about cdc-acm utilization.Application opens
> n_gsm tty and cdc-acm tty. cdc-acm tty connects to xhci device.
> The application configures cdc-adm tty to n_gsm tty as ldisc tty.
>
>     n_gsm=>cdc-acm=>xhci driver
>
> acm_tty_write can be called from n_gsm driver by ldisc connection,
> and from application when application opens cdc-acm tty directly.
> acm_tty_write wakes up the device by calling usb_autopm_get_interface_async,
> which calls pm_runtime_get. However, pm_runtime_get can't wake up
> the device before returning as it's an async wake up. Then, acm_tty_write
> might access the device when it is off.
>
> The patchset fixes it by:
> 1) add a new function usb_autopm_get_interface_upgrade to deal with
> above 2 requirements;
> 2) wake up device in n_gsm driver if n_gsm drivers calls cdc-acm driver;
>
> --
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