linux-kernel - Re: uio: add the uio

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Date:	Wed, 21 Jan 2009 21:06:12 +0100
From:	"Hans J. Koch" <hjk@...utronix.de>
To:	Brandon Philips <brandon@...p.org>
Cc:	"Hans J. Koch" <hjk@...utronix.de>, Greg KH <gregkh@...e.de>,
	linux-kernel@...r.kernel.org
Subject: Re: uio: add the uio_aec driver

On Wed, Jan 21, 2009 at 09:01:16AM -0800, Brandon Philips wrote:
> > The portio feature is available since .29-rc1, please use it.
> 
> Sounds good. I will rework it along with your suggestions below.

Fine. I had a look at their homepage, seems to be interesting hardware.

> 
> > > uioport is designed to be a setuid program and checks the permissions of
> > > the /dev/uio* node and if the user has write permissions it will use
> > > iopl and out*/in* to access the device.
> > 
> > What happens with PCI on PowerPC ?
> 
> I don't know. I could use /dev/port but my concern is that the device
> spec sheet specifies that some writes should be done with outb and
> others with outl. /dev/port only uses outb. Do you know if outl is
> different than four outb's to a device?

It is very probably different (4 WR pulses instead of one), the question
is if that causes different hardware behaviour. If there's a spec for it,
then you should definitly obey it.

What I had in mind was that those ioport regions cannot be mmapped on x86,
but it's possible on ppc, AFAIK.
Furthermore, you need to think about correct endianness handling.

Thanks,
Hans
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