Re: [rfc/patch] libata -- port configurable delays

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

On Gwe, 2005-05-13 at 21:03, Benjamin LaHaise wrote:
> > 3) IIRC some rare PATA devices don't like having their Status register 
> > banged "too hard".  No data, just a vague memory.

Not that I am aware of. There are a few ICH/PIIX variants where if you
read status during a transaction at the wrong time bad stuff occurs
including to the block on disk. That may be what you are thinking of

> > 
> > 4) It may be worthwhile to rewrite the loop to check the Status register 
> > _first_, then delay.

The 400nS delay after a command is required before status becomes valid.
This isn't about 'incorrect' devices in the command case. It is about
strictly correct behaviour and propogation/response times. For the cases
its not required and you wan to keep PCI load down then checking first
is clearly logical.

Also btw beware of PCI posting - writel/ndelay(400) isn't going to do
the right thing.