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

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Message-ID: <555D7DB4.6030606@linux.intel.com>
Date:	Thu, 21 May 2015 14:39:48 +0800
From:	"Lu, Baolu" <baolu.lu@...ux.intel.com>
To:	David Cohen <david.a.cohen@...ux.intel.com>,
	Sasha Levin <sasha.levin@...cle.com>
CC:	heikki.krogerus@...ux.intel.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



On 05/21/2015 05:22 AM, David Cohen wrote:
> Hi,
>
> On Wed, May 20, 2015 at 03:33:26PM -0400, Sasha Levin wrote:
>> 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;
>> +
> 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.

Thanks,
Baolu

>
>>   	drv->driver.bus = &ulpi_bus;
>>   
>>   	return driver_register(&drv->driver);
>> -- 
>> 1.7.10.4
>>
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>

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