linux-kernel - Re: [RFC PATCH 1/2] serial: 8250: Add a notifier chain for driver registration.

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Date:	Thu, 17 Mar 2011 11:42:19 -0700
From:	David Daney <ddaney@...iumnetworks.com>
To:	Grant Likely <grant.likely@...retlab.ca>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-serial@...r.kernel.org,
	gregkh@...e.de, linux-kernel@...r.kernel.org,
	devicetree-discuss@...ts.ozlabs.org
Subject: Re: [RFC PATCH 1/2] serial: 8250: Add a notifier chain for driver
 registration.

On 03/17/2011 11:25 AM, Grant Likely wrote:
> On Thu, Mar 17, 2011 at 12:18:49PM +0000, Alan Cox wrote:
>> On Wed, 16 Mar 2011 18:26:06 -0700
>> David Daney<ddaney@...iumnetworks.com>  wrote:
>>
>>> The 8250 driver is a bit weird in that in addition to supporting
>>> platform devices, extra devices can be added by calling
>>> serial8250_register_port().
>>>
>>> The problem is that if we call serial8250_register_port() before the
>>> driver is initialized Bad Things happen (we dereference NULL
>>> pointers).
>>>
>>> There doesn't seem to be a general way to know if a driver has been
>>> initialized
>>
>> I've had a bigger dig into this. I think the correct answer is probably
>> "always go via platform devices or similar". That *is* the notifier in
>> the kernel of today. serial8250_register_port ultimately should I think
>> ultimatly become an internal helper.
>
> +1
>
> Depending on serial8250_register_port() definitely the wrong thing to
> do for platform support code.  It would be better to figure out how to
> get the dt bits you need into 8250.c or of_serial.c.
>

IMHO, of_serial.c is no better than my board/chip specific code that 
calls serial8250_register_port().

Really what would be ideal would be a hook to add a dev.platform_data 
pointer to the appropriate struct plat_serial8250_port when the platform 
device is created.  It is possible that the platform bus notifiers could 
be used for this.  We would also want to have a way to add an 
of_device_id to those recognized by 8250.c

If we did that, serial8250_probe() would automatically do the right thing.

David Daney

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