Re: [Qemu-devel] Re: [PATCH] Always swap endianness in DBDMA

[Laurent Vivier]

Le mercredi 23 décembre 2009 à 10:55 +0000, Paul Brook a écrit :
> > The problem is that the whole define is just plain wrong which tells me
> > that the code is using the bswap functions incorrectly. This really
> > needs to be fixed by someone who knows the dbdma device. I don't see how
> > calling incorrect calls even more incorrect makes any difference.
> 
> The real problem is that devices shouldn't be doing byteswapping at all. This 
> should be determined by the (currently non-existant) bus layers and 
> implemented in generic code before the device callback.
> 
> The current code[1] is a nasty hack that sort-of works for most of the 
> current 
> machines because all devices happen to be connected the same way.  However 
> there are other machines (e.g. ixp4xx) some peripherals are connected 
> natively, whereas others are cross-wired.
> 
> On a related note, I'm not sure what the author of mac_bdbma.c was 
> smoking[2]. 

I didn't smoke... just need some sleep.

> It appears to keep register values in big-endian form for no good reason. 
> Much 
> easier would be to store them in native form, and just do the byteswapping 
> when accessed by the CPU.
> 
> Paul
> 
> [1] e.g. vga.c:vga_mem_readw
> [2] My guess is that the code is cribbed from elsewhere, and the original 
> source gave the CPU direct access to the ch->regs[] array.

>From pearpc io/macio/macio.cc.

Regards,
Laurent
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