linux-kernel - Re: [PATCH] usb: ulpi: don't register drivers if bus doesn't exist

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Message-ID: <20150521072133.GA16847@kuha.fi.intel.com>
Date:	Thu, 21 May 2015 10:21:33 +0300
From:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>
To:	"Lu, Baolu" <baolu.lu@...ux.intel.com>
Cc:	David Cohen <david.a.cohen@...ux.intel.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, balbi@...com
Subject: Re: [PATCH] usb: ulpi: don't register drivers if bus doesn't exist

> >>ULPI registers it's bus at module_init so if the bus fails to register, the
> >A minor comment: s/it's/its/
> >
> >>module will fail to load and all will be well in the world.
> >>
> >>However, if the ULPI code is built-in rather than a module, the bus
> >>initialization may fail but we'd still try to register drivers later onto
> >>a non-existant bus, which will panic the kernel.
> >>
> >>Fix that by checking that the bus was indeed initialized before trying to
> >>register drivers on top of it.
> >>
> >>Signed-off-by: Sasha Levin <sasha.levin@...cle.com>
> >>---
> >>  drivers/usb/common/ulpi.c |    4 ++++
> >>  1 file changed, 4 insertions(+)
> >>
> >>diff --git a/drivers/usb/common/ulpi.c b/drivers/usb/common/ulpi.c
> >>index 0e6f968..0b0a5e7 100644
> >>--- a/drivers/usb/common/ulpi.c
> >>+++ b/drivers/usb/common/ulpi.c
> >>@@ -132,6 +132,10 @@ int ulpi_register_driver(struct ulpi_driver *drv)
> >>  	if (!drv->probe)
> >>  		return -EINVAL;
> >>+	/* Was the bus registered successfully? */
> >>+	if (!ulpi_bus.p)
> >>+		return -ENODEV;

I think we need to warn in this case. How about:

        if (unlikely(WARN_ON(!ulpi_bus.p)))
                return -ENODEV;

> >Good catch. Otherwise it may trigger BUG() on driver_register().
> >I wonder if it would be nice to have a macro for that checking :)
> >
> >Anyway,
> >
> >Reviewed-by: David Cohen <david.a.cohen@...ux.intel.com>
> 
> Well, I was also encountering panic issue when running it on
> Intel Bay Trail tablets. In my case, it's due to the execution
> sequence. When ulpi bus is built-in, driver or device registered
> before ulpi bus registration.

This patch will fix the panic you saw as well, but of course we still
want the ulpi phy drivers to load successfully even if they and the
bus are build-in, so we need your patch as well.


Thanks,

-- 
heikki
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