Re: [PATCH 3/3] pata_amd: fix and improve cable detection

[Tejun Heo <htejun@gmail.com>]

Hello, again.  Forgot one thing.

Alan Cox wrote:
>> all we can use is how the BIOS configured it.  I suppose BIOS does it by
>> issuing trial commands which I don't think adding to libata is a good idea.
> 
> The BIOS does it by asking the hardware somehow. I traced one or two
> BIOSes that far. The info is there but its not documented in the
> slightest so only ACPI makes it visible via the BIOS.
> 
>> Can you please lemme know what you don't like about the current
>> implementation or what other approach you have in mind?  I don't like
>> Nvidia PATA either but there are a lot of people using it out there.
> 
> We seem to be able to trust the drives and BIOS ACPI data for Nvidia (at
> least what I have seen), so I guess we should simply declare the cable
> type unknown, 80 wire if ACPI says it is and then do the drive detect
> side ?

The drive side can't be trusted.  For the drive side detection work
properly, there should be a capacitor attached to PDIAG-:CBLID- line so
that the drive can tell 40C cable which connects CBLID- to the host
connector by sampling while the capacitor is still discharging.  If
there's no capacitor on the line, 40C and 80C cables behave identically.
 Voltage rises as soon as CBLID- is disasserted and drive always reports
80C and that's what happens on my A8N-E.  Hell of a way to save cost for
one capacitor, I guess.  :-(

-- 
tejun