Tejun Heo wrote:
Jeff, we've been ignoring PI in ahci_host_init()...
for (i = 0; i < probe_ent->n_ports; i++) {
#if 0 /* BIOSen initialize this incorrectly */
if (!(hpriv->port_map & (1 << i)))
continue;
#endif
The comment suggests that some BIOSen initialize PI incorrectly which
will probably result in undetected ports. Is this true? Would it be
dangerous to honor PI on some controllers? If so, PI should be used
only for controllers which does non-linear port mapping.
The core problem is that this register is write-once after reset, i.e.
BIOS-initialized. And my experience with pre-production machines has
been that after reset _by the driver_, the register was useless until
initialized to a value... _by the driver_. Which defeats the purpose of
the register.
So the info contained in the register is quite useful -- when info is
contained in the register. :)
Now, granted, I have only seen this on pre-production machines, hence
the #if 0. But also, since the code has been disabled in production, we
don't know how effective it is across all platforms, and we _do_ know
that it is ineffective if used directly after a reset. The write-once
behavior is documented, and normal.
We can't really know which controllers have a non-linear port mapping,
because that is dependent on both the silicon and whether or not the
chip is connected to port X[0-31]. The BIOS knows this, of course :)
We can try to enable the code, but I worry that it will fail in
situations such as kexec.
Jeff
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