Date:	Wed, 21 May 2008 08:49:38 +0200
From:	Uwe Kleine-König <Uwe.Kleine-Koenig@...i.com>
To:	Magnus Damm <magnus.damm@...il.com>
CC:	"Hans J. Koch" <hjk@...utronix.de>, <linux-kernel@...r.kernel.org>,
	<lethal@...ux-sh.org>, <gregkh@...e.de>, <linux-sh@...r.kernel.org>
Subject: Re: [PATCH 00/03][RFC] Reusable UIO Platform Driver

Hello Magnus,

Magnus Damm wrote:
> Hi Hans!
> 
> On Wed, May 21, 2008 at 6:07 AM, Hans J. Koch <hjk@...utronix.de> wrote:
> > On Tue, May 20, 2008 at 07:51:32PM +0900, Magnus Damm wrote:
> >> These patches implement a reusable UIO platform driver.
> >
> > Uwe Kleine-Koenig already submitted such a framework:
> >
> > http://lkml.org/lkml/2008/5/20/94
> >
> > It's his third version, and it looks good. I presume you didn't know
> > about his work. The main difference is that he leaves interrupt handling
> > to platform code. That might look strange (it did to me first), but it
> > has the advantage that you can put hardware dependent stuff in your
> > board support (which depends on hardware anyway).
> 
> I was not aware of this driver, thanks for the pointer!
> 
> > Could you have a look at his patch and tell me if that does what you
> > need?
> 
> The uio_pdrv driver doesn't do what I need at this point, though I may
> be able to extend it with the following:
> - Interrupt enable/disable code
> - Physically contiguous memory support
> 
> The interrupt code may be placed in the board/cpu code, but I need to
> share that code between multiple UIO driver instances. We want to use
> the same UIO driver for many different processor models and hardware
> blocks.
What about adding uio_platform_handler (with a different name) to
uio_pdrv.c?
OTOH I don't see why you want to disable the irq.  Can you describe the
reason?

>         Extending uio_pdrv driver with a chunk of physically
> contiguous memory isn't a big deal though.
I wonder how you use that memory.  Isn't it just some kind of shared
memory?  If so, why not use normal shared memory?  Do you really need
that?

> To be frank, I have my doubts in adding an extra forwarding-only
> platform layer on top of UIO compared to using uio_register_device()
> directly from the board code. I like that the platform layer is using
> struct resource and handles resource ranges for us automatically, but
> wouldn't it make more sense to extend the UIO core to always use
> struct resource instead of struct uio_mem? I'd be happy to help out -
> just point me in the right direction.
That alone doesn't help.  You need a struct device to register a uio
device.  So a platform device is the straight forward approach.
 
> >> The interrupt handling code in uio_platform assumes the device is the
> >> only user of the assigned interrupt.
> >
> > Uwe's approach doesn't have this limitation.
> 
> True, but the uio_pdrv driver is choosing to not deal with interrupts
> at all. I'd like to have shared interrupt handling code. With my
> driver, you just feed it io memory window parameters and an interrupt
> number and off you go. No need for any callbacks.
In my eyes this isn't completly correct.  Just the way you specify your
handler is a bit different.  You can pass a handler via platform data
with my driver, too.
 
BTW, you don't need "depends on UIO" (because it's in a if UIO/endif
block) and "default n" (as this is the default anyhow).  See also 
http://thread.gmane.org/gmane.linux.kernel/663884/focus=683097

Best regards
Uwe

-- 
Uwe Kleine-König, Software Engineer
Digi International GmbH Branch Breisach, Küferstrasse 8, 79206 Breisach, Germany
Tax: 315/5781/0242 / VAT: DE153662976 / Reg. Amtsgericht Dortmund HRB 13962
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