linux-kernel - Re: [PATCH 1/5] usb: phy: twl4030: make runtime pm more reliable.

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Date:	Thu, 26 Mar 2015 03:02:21 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	NeilBrown <neil@...wn.name>
CC:	Tony Lindgren <tony@...mide.com>, <linux-api@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>,
	GTA04 owners <gta04-owner@...delico.com>,
	NeilBrown <neilb@...e.de>, Pavel Machek <pavel@....cz>
Subject: Re: [PATCH 1/5] usb: phy: twl4030: make runtime pm more reliable.

Hi,

On Monday 23 March 2015 04:05 AM, NeilBrown wrote:
> From: NeilBrown <neilb@...e.de>
> 
> A construct like:
> 
>         if (pm_runtime_suspended(twl->dev))
>                pm_runtime_get_sync(twl->dev);
> 
> is against the spirit of the runtime_pm interface as it
> makes the internal refcounting useless.
> 
> In this case it is also racy, particularly as 'put_autosuspend'
> is use to drop a reference.
> When that happens a timer is started and the device is
> runtime-suspended after the timeout.
> If the above code runs in this window, the device will not be
> found to be suspended so no pm_runtime reference is taken.
> When the timer expires the device will be suspended, which is
> against the intention of the code.
> 
> So be more direct is taking and dropping references.
> If twl->linkstat is VBUS_VALID or ID_GROUND, then hold a
> pm_runtime reference, otherwise don't.
> Define "cable_present()" to test for this condition.

minor comment below..
> 
> Tested-by: Tony Lindgren <tony@...mide.com>
> Signed-off-by: NeilBrown <neilb@...e.de>
> ---
>  drivers/phy/phy-twl4030-usb.c |   29 ++++++++++++++++++++---------
>  1 file changed, 20 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/phy/phy-twl4030-usb.c b/drivers/phy/phy-twl4030-usb.c
> index 8e87f54671f3..1a244f34b748 100644
> --- a/drivers/phy/phy-twl4030-usb.c
> +++ b/drivers/phy/phy-twl4030-usb.c
> @@ -144,6 +144,16 @@
>  #define PMBR1				0x0D
>  #define GPIO_USB_4PIN_ULPI_2430C	(3 << 0)
>  
> +/*
> + * If VBUS is valid or ID is ground, then we know a
> + * cable is present and we need to be runtime-enabled
> + */
> +static inline bool cable_present(enum omap_musb_vbus_id_status stat)

twl4030_cable_present?

-Kishon
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