Re: Linux 2.6.25-rc4
- From: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
- Date: Sun, 16 Mar 2008 14:06:22 -0700 (PDT)
On Sun, 16 Mar 2008, Alan Cox wrote:
A _lot_ of chips require you to clear the DRQ by taking the data they
have.
Almost none and mostly very old ones.
Well, I admittedly haven't been involved in IDE in about a decade, so
yeah, maybe it's simply no longer true. That said, if the second bisection
was accurate (which is admittedly a rasonably big "if"), it really looks
like it would be related to the fact that we used to empty the data buffer
before handling errors for REQ_TYPE_ATA_CMD commands.
Not in my experience having maintained a lot of ATA drivers for a very
long time. In fact the changes for draining the DRQ went into libata only
very recently because it was only when we had a distro sized userbase
with PATA devices that it became apparent that a few corner case problems
remained.
.. but as you noticed, it's almost never wrong to drain (the only chipset
it's marked for is some broken pdc202xx one), and it definitely *is* wrong
not to drain.
Also, one reason you'd not necessarily even see this is that with DMA,
this is a non-issue (since the hardware DMA engine will be doing all the
draining), so in order to ever see this you have to still use PIO _and_
you have to see IDE command errors in the first place _and_ you have to
have a device that actually keeps DRQ enabled even at an error.
All of which are hopefully fairly rare by now (and getting rarer, at last
for the PIO one).
I also wouldn't be entirely surprised if the DRQ behavior may even be
command-specific, with the regular data path for read/write quite possibly
being different from the special commands that go through some internal
drive firmware logic paths.
So I could well imagine (for example) that when a drive raises an IO error
due to a read or write fault, the DRQ line will be cleared by the drive,
but that special commands might have some firmware-directed separate FIFO
that needs draining.
Linus
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- References:
- Linux 2.6.25-rc4
- From: Linus Torvalds
- Re: Linux 2.6.25-rc4
- From: Anders Eriksson
- Re: Linux 2.6.25-rc4
- From: Linus Torvalds
- Re: Linux 2.6.25-rc4
- From: Bartlomiej Zolnierkiewicz
- Re: Linux 2.6.25-rc4
- From: Linus Torvalds
- Re: Linux 2.6.25-rc4
- From: Alan Cox
- Re: Linux 2.6.25-rc4
- From: Linus Torvalds
- Re: Linux 2.6.25-rc4
- From: Alan Cox
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