linux-kernel - RE: [PATCH UCC TDM 1/3 Updated] Platform changes for UCC TDM driver for MPC8323eRDB. Also includes related QE changes and dts entries.

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Date:	Fri, 25 Jan 2008 09:39:05 +0530
From:	"Aggrwal Poonam" <Poonam.Aggrwal@...escale.com>
To:	<avorontsov@...mvista.com>, "Tabi Timur" <timur@...escale.com>
Cc:	"Gala Kumar" <kumar.gala@...escale.com>,
	<akpm@...ux-foundation.org>, <linux-kernel@...r.kernel.org>,
	<netdev@...r.kernel.org>, <rubini@...ion.unipv.it>,
	<linuxppc-dev@...abs.org>,
	"Barkowski Michael" <Michael.Barkowski@...escale.com>,
	"Cutler Richard" <Rich.Cutler@...escale.com>,
	"Kalra Ashish" <ashish.kalra@...escale.com>
Subject: RE: [PATCH UCC TDM 1/3 Updated] Platform changes for UCC TDM driver for MPC8323eRDB. Also includes related QE changes and dts entries.

Hello Anton/Tabi

I am not sure which is the best place to configure the pins. Because
some drivers do it in one way and some in the other.
I actually tried to make the driver similar to ucc_geth because it is a
QE driver. The driver has no platform code in the platform files similar
to ucc_geth. It is probed along with all the QE devices thorugh
of_platform_bus_probe.
And the pins are configured for all the QE devices using  par_io_init.
I thought this to be the most consistent way at that time.

How should we close this point?
Can we go ahead with the pio-map?

Infact the discussion in this thread was very good and I got to know a
lot of rationales behind this.

Please suggest.

Thanks and Regards
Poonam

From: Anton Vorontsov [mailto:avorontsov@...mvista.com] 
Sent: Thursday, January 24, 2008 10:53 PM
To: Tabi Timur
Cc: Aggrwal Poonam; Gala Kumar; akpm@...ux-foundation.org;
linux-kernel@...r.kernel.org; netdev@...r.kernel.org;
rubini@...ion.unipv.it; linuxppc-dev@...abs.org; Barkowski Michael;
Cutler Richard; Kalra Ashish
Subject: Re: [PATCH UCC TDM 1/3 Updated] Platform changes for UCC TDM
driver for MPC8323eRDB. Also includes related QE changes and dts
entries.

On Thu, Jan 24, 2008 at 10:33:47AM -0600, Timur Tabi wrote:
> Anton Vorontsov wrote:
> 
> >Are you saying that TDM is sharing same pins with the other QE 
> >device, and we can choose to use/not use some device depending on 
> >which driver is loaded?
> 
> No.  I'd have to closely examine the DTS, but I don't think that UCC 
> devices share pins at all.  But that isn't my point.
> 
> >In that particular case UCC configuration is static, for every UCC.
> >So, we can set up all pins in the firmware/board file.
> 
> Yes, but deciding what the UCC does might not be static.  At what 
> point do we declare, "UCC5 is for eth0 and eth0 only"?
> 
> The advantage of putting the pin configurations in the device tree is 
> that they now become configurable.  I can envision a scenario where 
> UCC5 could be either an Ethernet or a UART, depending on the setting 
> of some jumpers on the board. That's what the QE was designed for: any

> UCC can do any task, and you can even have a UCC change its purpose
while the system is running.
> So I don't want the pin configurations hard-coded into the kernel.  
> Having them in the device tree gives me some flexibility.

If hardware configuration is selected at the bootup time, by jumpers or
switches, it's even easier to do it right. Without pio-map.

> For instance, I have a plan (that I keep postponing) to introduce a 
> new feature in U-Boot where U-Boot can determine the settings of some 
> board jumpers and modify the device tree accordingly. The instructions

> on how to modify the device tree would be embedded in the tree itself.

Why you need to modify the device tree for that? Let the U-Boot simply
setup pins for the kernel. Regarding kernel overwriting pins
configuration...

> I can't
> support this feature if the kernel calls par_io_config_pin() 
> regardless of what's in the device tree.

What I've understood from the previous debates, is that ideally kernel
should not touch pins' configuration. Today we're using pio-map solely
to fix up some old firmware misconfiguration. And we can do this in the
board file still. To determine if we need to fixup the firmware or not,
we can use some device tree property instead (firmware version?).

p.s.
I'm neither for pio-map nor against. I just want some consequence
regarding this. Last thread ended with consequence that pio-map is a bad
thing to use...

--
Anton Vorontsov
email: cbou@...l.ru
backup email: ya-cbou@...dex.ru
irc://irc.freenode.net/bd2
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