ata: libata-eh: Avoid unnecessary resets when revalidating devices

ata: libata-eh: Avoid unnecessary resets when revalidating devices

In ata_eh_revalidate_and_attach(), a link LPM policy is always
set to ATA_LPM_MAX_POWER before calling ata_dev_revalidate() to ensure
that the call to ata_phys_link_offline() does not return true, thus
causing an unnecessary device reset. This change was introduced
with commit 71d7b6e51ad3 ("ata: libata-eh: avoid needless hard reset
when revalidating link").

However, setting the link LPM policy to ATA_LPM_MAX_POWER may be
visible only after some time, depending on the power state the link was
in. E.g. transitioning out of the Partial state should take no longer
than a few microseconds, but transitioning out of the Slumber or
DevSleep state may take several milliseconds. So despite the changes
introduced with commit 71d7b6e51ad3 ("ata: libata-eh: avoid needless
hard reset when revalidating link"), we can still endup with
ata_phys_link_offline() seeing a link SCR_STATUS register signaling that
the device is present (DET is equal to 1h) but that the link PHY is
still in a low power mode (e.g. IPM is 2h, signaling "Interface in
Partial power management state"). In such cases, ata_phys_link_offline()
returns true, causing an EIO return for ata_eh_revalidate_and_attach()
and a device reset.

Avoid such unnecessary device resets by introducing a relaxed version
of the link offline test implemented by ata_phys_link_offline() with
the new helper function ata_eh_link_established(). This functions
returns true if for the link SCR_STATUS register we see that:
 - A device is still present, that is, the DET field is 1h (Device
   presence detected but Phy communication not established) or 3h
   (Device presence detected and Phy communication established).
 - Communication is established, that is, the IPM field is not 0h,
   indicating that the PHY is online or in a low power state.

Signed-off-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Link: https://lore.kernel.org/r/20250701125321.69496-5-dlemoal@kernel.org
Signed-off-by: Niklas Cassel <cassel@kernel.org>