Messages in this thread | | | From | Bartlomiej Zolnierkiewicz <> | Subject | Re: Worrisome IDE PIO transfers... | Date | Sun, 29 Feb 2004 15:55:49 +0100 |
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On Sunday 29 of February 2004 09:50, Geert Uytterhoeven wrote: > On Sun, 29 Feb 2004, Bartlomiej Zolnierkiewicz wrote: > > [ Geert added to cc: ] > > > > On Sunday 29 of February 2004 00:24, Jeff Garzik wrote: > > > Looking at the function that is used to transfer data when in PIO > > > mode... > > > > > > void taskfile_output_data (ide_drive_t *drive, void *buffer, u32 > > > wcount) { > > > if (drive->bswap) { > > > ata_bswap_data(buffer, wcount); > > > HWIF(drive)->ata_output_data(drive, buffer, wcount); > > > ata_bswap_data(buffer, wcount); > > > } else { > > > HWIF(drive)->ata_output_data(drive, buffer, wcount); > > > } > > > } > > > > > > Swapping the data in-place is very, very wrong... you don't want to > > > be touching the data that userspace might have mmap'd ... > > > Additionally, byteswapping back and forth for each PIO sector chews > > > unnecessary CPU. > > > > This is used for accessing "normal" disks on beasts with byte-swapped IDE > > bus (Atari/Q40/TiVo) and "byteswapped" disks on normal machines. > > > > [ Hm. actually I don't see how it can be used for accessing "normal" > > disks, as data is byteswapped by IDE bus and then swapped back by IDE > > driver. ] > > Why not? The only difference between `normal' and `byteswapped' disks is > that the bytes in a 16-bit word are swapped (sic :-), so you can convert in > both directions by swapping the bytes. Normal disks have been used on Atari > before, so it should (still) work.
Oh yes, IDE driver fixes byteorder on Atari/Q40 only when "bswap" is used.
> BTW, the generic tree misses this patch, which was deemed inappropriate > before, but is needed to make sure the drive identification block is > correct on those machines:
Thanks. I can't see a smarter way to fix this now. :/
Bartlomiej
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