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

[Tejun Heo <htejun@gmail.com>]

Mark Lord wrote:
>>> 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:

Aieee...

> 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.

The usual way to handle this is to clear the controller state (not the 
PHY) from ->error_handler() before calling the generic error_handler. 
Many drivers do similar things - ahci restarts the engine, sil24 calls 
sil24_init_port() and so on.  Does mv need PHY reset to get it working 
again?

-- 
tejun