Re: todays git: WARNING: at drivers/ata/libata-sff.c:1017 ata_sff_hsm_move+0x45e/0x750()

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Alan Cox wrote:

O> Your problem is that the *device* is wanting to transfer a set of bytes

not divisible by four.  If you want to use word based PIO, you'll have
to fall back to collecting bytes for the last two.  Alternatively, you

Nope.. you can't do that with ATA block transfers - it isn't the same as
SCSI

ATA block transfers are always mutliple of 512 bytes (except read/write long), so this shouldn't be an issue... unless the code is trying to split a sector between 2 pages on an arbitrary boundary -- in this case, even if the both resulting byte counts divide by 2, you may be busted because of prefetch that (as the Intel docs say), should have the initial (start of sector) and all subsequent reads of the same size (either 16- or 32-bit). I don't know if this situation is actually possible with libata -- but beware...

could just do byte PIO for all reply lengths like this ... they occur
all over the SCSI standard, but not usually in critical paths.

The problem we have is that the sg list the drivers were given had a
segment which was not divisible in length by four and was *NOT* the last
segment in the sg list

The logic in the ATA PIO code is basically

	for each sg entry

		compute the number of bytes to transfer staying within
the page
		transfer that many bytes (but may be more)

		if and only if the transfer is NOT the last segment but is
			more than the bytes requested - WARN

The ATAPI logic is more complex since it has to take into account the arbitrary byte count that a device want to transfer on each INTRQ (read from the byte count low/high regs).

Alan

MBR, Sergei
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