Re: libata-eh/pmp command sequence on NCQ media error

[Mark Lord <liml@rtr.ca>]

Mark Lord wrote:
> Tejun Heo wrote:
>> Mark Lord wrote:
>>>> So why are we taking a hammer to things there?
>>
>> Hmmm... The reset action might be too heavy handed but maybe keeping 
>> that categorized as ATA bus error is still a good idea so that 
>> multiple errors w/ that bit set can trigger speed down.
>>
>>> FWIW, this patch fixes it for me (and fixes a misleading printk).
>>> Or I could just clear that bit from sata_mv before invoking EH.
>>> (??)
>>
>> Does the bit get set for the host link or pmp fanout links?
> It's only on the pmp fanout link. Dunno why it gets set, but it does.
..

Oh, wait a sec.. I think I know what's going on.
We're back to the original problem in this thread again:

Mark Lord wrote:
> With no port-multiplier attached, a media error during NCQ
> results in an immediate READ_LOG_EXT_10H to retrieve the
> task file for the failed I/O.
> 
> With a port-multiplier, there is instead a flurry of sata_pmp_read()
> attempts.  I'm guessing that the READ_LOG_EXT_10H would normally
> then follow those ?
> 
> The problem is, on most of the Marvell chips, non-data commands
> cannot succeed after any kind of error (until after the port is reset),
> so they fail, and we never then get to the READ_LOG_EXT_10H stage.
> Oddly, the READ_LOG_EXT_10H command itself is okay (with some errata
> goodness tossed in).
> 
> So, for sata_mv at least, I'd kinda like to have libata-eh attempt
> the READ_LOG_EXT_10H before it tries to (unsuccessfully) access the
> per-port SCRs on the PMP.
..

So what is happening now, is that libata-eh is going and attempting
to access the per-port SCRs *after* the READ_LOG_EXT commands.
And those per-port SCRs are not actually accessible:  the shadow
registers are misbehaving -- known errata -- and cannot be accurately
used without a port reset.

Mmm.. gotta figure out a way to mark the port for RESET,
without having that action taint the commands already analyzed.

I suppose I'll have to just clone some code from libata-eh to
do the READ_LOG_EXT and then qc_complete() those commands
before continuing.  Or something.

???