From mboxrd@z Thu Jan  1 00:00:00 1970
From: Takashi Iwai <tiwai@suse.de>
Subject: Re: Re: hdsp on big-endian
Date: Wed, 22 May 2002 15:47:17 +0200
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To: Paul Davis <pbd@op.net>
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List-Id: alsa-devel@alsa-project.org

At Wed, 22 May 2002 09:29:57 -0400,
Paul Davis wrote:
> 
> >> >anyway...  after looking at the hdsp code again, i found that these
> >> >endian conversions are not necessary at all!
> >> >IIRC, readX/writeX already convert the endianess in itself.  thus, the
> >> 
> >> absolutely not. readl/writel on most architectures translate to:
> >> 
> >> 	   *addr = val;
> >> 
> >
> >really?  for example, ppc uses in_le32() for readl(), which implies
> >byte swapping.
> 
> what does CONFIG_APUS do? thats the conditional on which in_le32 is
> used or not. AFAIK, readl is not supposed to have
> endian-characteristics, but if true, that would make the non-APUS ppc
> version totally wrong.

CONFIG_APUS is for amiga.  it's not set usually.
i have no idea about APUS, but it looks like the BE interface.

basically PCI bus is accessed as LE.  that's why in_le32 is used
there.  we can access to io without considration of endianess as long
as using readX/writeX.  (for direct access, you can use __raw_readX()
macros.)


> on x86:
> 
> #define __io_virt(x) ((void *)(x))
> #define readl(addr) (*(volatile unsigned int *) __io_virt(addr))
> #define writel(b,addr) (*(volatile unsigned int *) __io_virt(addr) = (b))

yep, on LE architectures, no conversion is necessary.


Takashi

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