Re: libata-scsi: ata_to_sense_error handling status 0x40

[Damien Le Moal <damien.lemoal@opensource.wdc.com>]

On 8/31/22 22:30, Peter Fröhlich wrote:
> Sorry for spamming replies and quoting myself.
> 
> On Wed, Aug 31, 2022 at 12:21 PM Peter Fröhlich
> <peter.hans.froehlich@gmail.com> wrote:
>> On Wed, Aug 31, 2022 at 9:48 AM Damien Le Moal
>> <damien.lemoal@opensource.wdc.com> wrote:
>>> On 8/31/22 16:15, Hannes Reinecke wrote:
>>>> Oh, of course :-)
>>>> That was when doing SMR support for libata.
>>>> I dimly remember that some pre-spec drives had been using the DRDY bit
>>>> to signal an unaligned write. Which never made it into the spec, but the
>>>> decoding stayed.
>>>
>>> Any idea where the other bits come from ? Except for bit 5 (device fault),
>>> I do not see anything else in the specs that mandate these definitions...
>>
>> I have since discovered the "SCSI to ATA" specification which has two
>> tables about mapping ATA errors to SCSI errors. Among those I was able
>> to find an "unaligned write" case as well, but I cannot properly parse
>> the rest of the two tables yet. They are in sections 11.6 and 11.7 of
>> that document.
> 
> So I've re-read everything I can get my hands on and from what I can
> tell the overall "flow" of ata_to_sense_error() is not what the
> specifications would imply. For example we look at BSY on entry and
> then say "ah, it's set, then let's ignore the error field" when the
> specification (the way I read it) instead says "BSY is transport
> dependent, so we say nothing about it here; but check the error bit in
> status, if it is set, interpret the error field, otherwise there's
> nothing for you in the error field". Of course I am a complete noob
> when it comes to this ATA/SATA/SCSI/AHCI stuff, so please divide by at
> least two. Sorry if this adds more confusion on top.

I had a quick look at the specs again. I already spotted an error: when
the status device fault bit is set, the sense should be HARDWARE ERROR /
INTERNAL TARGET FAILURE and not ABORTED COMMAND / 0x47 like now. That is
according to SAT-5. But looking at ACS-5, sections 6 and 7.1.6, there are
*a lot* of cases that need to be taken care of. It looks like the
sense_table does that, but need to cross check.

As for the stat_table, except for the first buggy entry as mentioned
above, I have no clue where these come from. SAT only defines the HARDWARE
ERROR / INTERNAL TARGET FAILURE for when the status field device fault bit
is set. Need to dig further, but I am afraid this code may be due to years
of supporting drives returning weird errors that got mapped to sensible
sense codes instead of a pure implementation of the specs...

I need to spend some quality time with ACS and SAT documents to sort out
this one... And lots of coffee too probably :)

> 
> Cheers,
> Peter


-- 
Damien Le Moal
Western Digital Research