On Fri, Feb 18, 2000, Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
wrote:
>> Does anyone have any objection if I make insw/outsw/insl/outsl *not*
>> byte-swap the data? The reason is that these functions are mostly used
>> for transferring blocks of data, i.e. arrays of bytes. I haven't found a
>> single instance where they are used for transferring arrays of 16 or
>> 32-bit words.
>>
>> This would mean that we wouldn't need the kludge in the ide stuff where we
>> redefine insw as ide_insw (which doesn't byte-swap). There is currently a
>> bug there because insl does still byte-swap, which means that if you set
>> the -c1 flag with hdparm, you get byte-swapped data. :-(
>
>Hmm... This is indeed ambiguous. Is e.g. insl() used to (a) read n 32-bit
>words
>from (little endian) ISA I/O space, or (b) used to read n*4 bytes from
ISA I/O
>space, using 32-bit accesses?
>
>What about moving this to linux-kernel? It affects all big endian platforms.
My original reply to Paul's post didn't make it to the list, so here it is:
My understanding is that those routines are used to "pump" or write
to/from a fifo containing a bytestream. For example, IDE is a bytestream
fifo that is usually 16 bits wide (but can be 32). A sound card is a byte
stream too (the endian ordering of samples is a different issue). So we
always fall in cases where datas must not be swapped.
Anyway, if you want to have in memory the same data pattern you have on a
LE platform, then you must not byteswap (if you don't see why, just
imagine that the i386 will endian swap when reading the port and endian
swap again when writing to memory, which is equivalent of a read&write
without swap). The width of the fifo is in fact irrelevant.
So yes, I beleive Paul is right and this should be done on all BE archs.
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