linux-kernel - Re: [PATCH 1/3] serial/imx: add device tree support

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Date:	Thu, 23 Jun 2011 08:12:35 +0800
From:	Shawn Guo <shawn.guo@...escale.com>
To:	Grant Likely <grant.likely@...retlab.ca>
CC:	<patches@...aro.org>, <netdev@...r.kernel.org>,
	<devicetree-discuss@...ts.ozlabs.org>,
	Jason Liu <jason.hui@...aro.org>,
	<linux-kernel@...r.kernel.org>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	<linux-arm-kernel@...ts.infradead.org>,
	David Gibson <david@...son.dropbear.id.au>
Subject: Re: [PATCH 1/3] serial/imx: add device tree support

On Wed, Jun 22, 2011 at 09:52:11AM -0600, Grant Likely wrote:
[...]
> 
> >> > -       line = of_get_property(node, "id", NULL);
> >> > -       if (!line)
> >> > +       line = of_get_device_index(node, "serial");
> >> > +       if (IS_ERR_VALUE(line))
> >> >                return -ENODEV;
> >>
> >> Personally, it an alias isn't present, then I'd dynamically assign a port id.
> >>
> > We probably can not.  The driver works with being told the correct
> > port id which is defined by soc.  Instead of dynamically assigning
> > a port id, we have to tell the driver the exact hardware port id of
> > the device that is being probed.
> 
> Are you sure?  It doesn't look like the driver behaviour uses id for
> anything other than an index into the statically allocated serial port
> instance table.  I don't see any change of behaviour based on the port
> number anywhere.
> 
Sorry, I did not make this clear.  In serial_imx_probe(), the port
gets created and then saved as below.

	imx_ports[sport->port.line] = sport;

While in imx_console_setup(), it addresses the port as following.

	sport = imx_ports[co->index];

When users specify their console as ttymxc0, they mean they are
using the first i.mx uart hardware port, in turn ttymxc1 for the
second port ...

That said, imx_port[0] has to be the first hardware port, imx_port[1]
has to be the second one ...  That's why port id sport->port.line
can not be dynamically assigned, otherwise console may not work.

-- 
Regards,
Shawn

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