From: David Hawkins <dwh@ovro•caltech.edu>
To: Stefan Roese <sr@denx•de>
Cc: linuxppc-embedded@ozlabs•org
Subject: Re: Yosemite/440EP why are readl()/ioread32() setup to read little-endian?
Date: Wed, 25 Jan 2006 10:26:55 -0800 [thread overview]
Message-ID: <43D7C2EF.5060508@ovro.caltech.edu> (raw)
In-Reply-To: <200601251057.47619.sr@denx.de>
Hi Stefan,
>>readl() and ioread32() read the registers in little-endian format!
>
> Correct. That's how it is implemented on all platforms. Think for example of
> an pci device driver. Using these IO functions, the driver will become
> platform independent, running without modifications on little- and big-endian
> machines.
Ok, I figured that was probably the case. Thanks for the confirmation.
>>Should I just be using pointers for remapped processor
>>registers, and only use readl(), ioread32(), etc, on external
>>memory?
>
> That's how I do it. Only use readl() and friends for pci spaces (or other
> little endian memory mapped areas).
I took a look at the Yosemite network and USB drivers, it looks like
the authors of those drivers chose to use in_be32() and out_be32().
Personally I like the concept of using pointers, or more usefully
pointers to structure overlays for device control. However, the
impression I have is that this is inherently more non-portable
than using the readl()/writel(), ioread32()/iowrite32(), and
now I guess I can add in_be32()/out_be32() to that list.
But if you use pointers, thats good enough for me!
Cheers
Dave
next prev parent reply other threads:[~2006-01-25 18:29 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-17 0:45 [Patch 3/3] Add Yellowstone Platform defconfig John Otken
2006-01-24 18:08 ` Yosemite/440EP why are readl()/ioread32() setup to read little-endian? David Hawkins
2006-01-24 19:07 ` Yosemite/440EP is there a global interrupt enable mask? David Hawkins
2006-01-25 10:28 ` Stefan Roese
2006-01-25 18:30 ` David Hawkins
2006-01-25 18:55 ` Eugene Surovegin
2006-01-25 19:46 ` David Hawkins
2006-01-25 20:13 ` Eugene Surovegin
2006-01-25 20:34 ` David Hawkins
2006-01-25 9:57 ` Yosemite/440EP why are readl()/ioread32() setup to read little-endian? Stefan Roese
2006-01-25 18:26 ` David Hawkins [this message]
2006-01-25 18:51 ` Eugene Surovegin
2006-01-25 19:36 ` David Hawkins
2006-01-25 19:48 ` Eugene Surovegin
2006-01-26 10:20 ` Stefan Roese
2006-01-27 0:10 ` David Hawkins
2006-01-27 23:29 ` David Hawkins
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