Re: [PATCH] ahci: fix CAP.NP and PI handling

[Jeff Garzik <jeff@garzik.org>]

Tejun Heo wrote:
> AHCI uses CAP.NP to indicate the number of ports and PI to tell which
> ports are enabled.  The only requirement is that the number of ports
> indicated by CAP.NP should equal or be higher than the number of
> enabled ports in PI.
> 
> CAP.NP and PI carry duplicate information and there have been some
> interesting cases.  Some early AHCI controllers didn't set PI at all
> and just implement from port 0 to CAP.NP.  An ICH8 board which wired
> four out of six available ports had 3 (4 ports) for CAP.NP and 0x33
> for PI.  While ESB2 has less bits set in PI than the value in CAP.NP.
> 
> Till now, ahci driver assumed that PI is invalid if it doesn't match
> CAP.NP exactly.  This violates AHCI standard and the driver ends up
> accessing unmimplemented ports on ESB2.
> 
> This patch updates CAP.NP and PI handling such that PI can have less
> number of bits set than indicated in CAP.NP and the highest port is
> determined as the maximum port of what CAP.NP and PI indicate.
> 
> Signed-off-by: Tejun Heo <htejun@gmail.com>
> Cc: Jan Beulich <jbeulich@novell.com>

applied