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

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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>
This commit is contained in:
Damien Le Moal 2025-07-01 21:53:15 +09:00 committed by Niklas Cassel
parent b1f5af54f1
commit 4371fe1ba4
1 changed files with 28 additions and 1 deletions
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29
drivers/ata/libata-eh.c
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@ -2071,6 +2071,33 @@ static void ata_eh_get_success_sense(struct ata_link *link)
ata_eh_done(link, dev, ATA_EH_GET_SUCCESS_SENSE);
}
/*
* Check if a link is established. This is a relaxed version of
* ata_phys_link_online() which accounts for the fact that this is potentially
* called after changing the link power management policy, which may not be
* reflected immediately in the SSTAUS register (e.g., we may still be seeing
* the PHY in partial, slumber or devsleep Partial power management state.
* So check that:
* - A device is still present, that is, DET is 1h (Device presence detected
* but Phy communication not established) or 3h (Device presence detected and
* Phy communication established)
* - Communication is established, that is, IPM is not 0h, indicating that PHY
* is online or in a low power state.
*/
static bool ata_eh_link_established(struct ata_link *link)
{
u32 sstatus;
u8 det, ipm;
if (sata_scr_read(link, SCR_STATUS, &sstatus))
return false;
det = sstatus & 0x0f;
ipm = (sstatus >> 8) & 0x0f;
return (det & 0x01) && ipm;
}
/**
* ata_eh_link_set_lpm - configure SATA interface power management
* @link: link to configure
@ -3275,7 +3302,7 @@ static int ata_eh_revalidate_and_attach(struct ata_link *link,
goto err;
}
if (ata_phys_link_offline(ata_dev_phys_link(dev))) {
if (!ata_eh_link_established(ata_dev_phys_link(dev))) {
rc = -EIO;
goto err;
}