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 12:47:23 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	David Daney <ddaney@...iumnetworks.com>
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 Thu, Mar 17, 2011 at 11:42:19AM -0700, David Daney wrote:
> 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.

Take a look at the way arch/powerpc/platforms/512x/pdm360ng.c uses a
notifier for amending a platform_device with additional data..

g.

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