Re: Port Multiplier drives not always all found on cold plug

[Mark Lord <liml@rtr.ca>]

Mark Lord wrote:
> Mark Lord wrote:
>> Mark Lord wrote:
>>> Tejun,
>>>
>>> Since enabling PMP support in sata_mv, there have been some recent
>>> reports of not all drives being found on a PM.
> ..
>> Mmmm.. one strange thing from the logs.
>> sata_mv reports "unexpected device interrupt" in a few places,
>> and then triggers EH to recover from it.
>> This could be what is causing the PMP enumerations to partially fail.
>>
>> I wonder why we're getting interrupts when supposedly idle/polling ?
>> Did something in libata miss reading ata_status to clear an IRQ ?
> ..
> 
> Here, I've hacked my local copy of sata_mv to NOT trigger EH
> when it gets an unexpected device interrupt.  This is how the driver
> has been for years, until recently.
> 
> With this change, all drives on the PM are found (no surprise).
> 
> So I guess the questions are:
> 
> 1. Where are these unexpected interrupts coming from?
> 
> The implication is that a command is being issued without NIEN=1,
> *or* the ata_status is not being read (to clear the pending IRQ)
> before we clear NIEN for a subsequent command.
..

Mmm.. libata looks totally clean there, verified with some printk's
placed in strategic locations.

Perhaps all commands to the PM itself (pmp=15) result in interrupts
on receipt of the response?  The PM spec certainly implies this,
and doesn't mention NIEN at all.

I suppose that could be the source of them -- tracing in the driver
suggests that they all happen during/after issue of a PMP read command.

> 2. What to do about them in the driver?
..

I think by default, I'll just revert to having the driver ignore them,
the same as is done in the default methods in libata-core.c.

So far they do seem harmless in my testing here.

??