linux-kernel - Re: [PATCH] usb: musb: call pm_runtime_{get,put}

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Date:   Mon, 26 Feb 2018 09:57:16 -0600
From:   Bin Liu <b-liu@...com>
To:     Merlijn Wajer <merlijn@...zup.org>
CC:     <linux-omap@...r.kernel.org>, <tony@...mide.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        <linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: musb: call pm_runtime_{get,put}_sync before reading
 vbus registers

Hi,

On Mon, Feb 26, 2018 at 11:56:08AM +0100, Merlijn Wajer wrote:
> Without pm_runtime_{get,put}_sync calls in place, reading
> vbus status via /sys causes the following error:
> 
> Unhandled fault: external abort on non-linefetch (0x1028) at 0xfa0ab060
> pgd = b333e822
> [fa0ab060] *pgd=48011452(bad)
> 
> [<c05261b0>] (musb_default_readb) from [<c0525bd0>] (musb_vbus_show+0x58/0xe4)
> [<c0525bd0>] (musb_vbus_show) from [<c04c0148>] (dev_attr_show+0x20/0x44)
> [<c04c0148>] (dev_attr_show) from [<c0259f74>] (sysfs_kf_seq_show+0x80/0xdc)
> [<c0259f74>] (sysfs_kf_seq_show) from [<c0210bac>] (seq_read+0x250/0x448)
> [<c0210bac>] (seq_read) from [<c01edb40>] (__vfs_read+0x1c/0x118)
> [<c01edb40>] (__vfs_read) from [<c01edccc>] (vfs_read+0x90/0x144)
> [<c01edccc>] (vfs_read) from [<c01ee1d0>] (SyS_read+0x3c/0x74)
> [<c01ee1d0>] (SyS_read) from [<c0106fe0>] (ret_fast_syscall+0x0/0x54)
> 
> Solution was suggested by Tony Lindgren <tony@...mide.com>.
> 
> Signed-off-by: Merlijn Wajer <merlijn@...zup.org>
> ---
>  drivers/usb/musb/musb_core.c | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/drivers/usb/musb/musb_core.c b/drivers/usb/musb/musb_core.c
> index eef4ad578b31..ceaa40ef0e73 100644
> --- a/drivers/usb/musb/musb_core.c
> +++ b/drivers/usb/musb/musb_core.c
> @@ -1760,6 +1760,8 @@ vbus_show(struct device *dev, struct device_attribute *attr, char *buf)
>  	val = musb->a_wait_bcon;
>  	vbus = musb_platform_get_vbus_status(musb);
>  	if (vbus < 0) {
> +		pm_runtime_get_sync(dev);
> +
>  		/* Use default MUSB method by means of DEVCTL register */
>  		devctl = musb_readb(musb->mregs, MUSB_DEVCTL);
>  		if ((devctl & MUSB_DEVCTL_VBUS)
> @@ -1767,6 +1769,8 @@ vbus_show(struct device *dev, struct device_attribute *attr, char *buf)
>  			vbus = 1;
>  		else
>  			vbus = 0;
> +
> +		pm_runtime_put_sync(dev);
>  	}
>  	spin_unlock_irqrestore(&musb->lock, flags);

Thanks for the patch, but I got spinlock deadlock when testing it. I
think the function pair should be at the outside scope of the
spin_lock/unlock, doesn't it?

Regards,
-Bin.