Re: [PATCH v2] ata: ahci: work around lost interrupts on Marvell 88SE61xx

[Damien Le Moal <dlemoal@kernel.org>]

On 8/28/26 16:05, Hajo Noerenberg wrote:
> 
> ahci_single_level_irq_intr() services the ports first and clears the
> global HOST_IRQ_STAT afterwards, as recommended by AHCI 1.1 section
> 10.6.2.  The Marvell 88SE6111/6121/6145 family stops reporting interrupts
> for a port when HOST_IRQ_STAT is cleared while PxIS still holds bits:
> PxIS keeps its content, HOST_IRQ_STAT reads back as 0, the port is never
> looked at again, and the command in flight only ends in a timeout.
> 
> Measured on a Seagate Blackarmor NAS440 (Marvell 88F6281 Kirkwood,
> 88SE6121 rev B2 behind PCIe) by polling the AHCI registers from userspace
> while an IDENTIFY was outstanding:
> 
>   t=303.046  irqs 127  PxIS 0x00000000  PxCI 0x00000001
>              IDENTIFY issued
>   t=303.057  irqs 128  PxIS 0x00000020  PxCI 0x00000000
>              CI cleared, DPS set, one interrupt taken
>              ... PxIS stays 0x00000020, HOST_IRQ_STAT stays 0 ...
>   t~308.05   qc timeout after 5000 msecs
> 
> The command had completed - PxCI was clear and PxIS had DPS set - so
> ahci_qc_complete() would have completed it.  It never got the chance
> because the handler read HOST_IRQ_STAT as 0 and returned IRQ_NONE.
> 
> Marvell's own driver for these chips clears the two registers in the
> opposite order and says so ("clear global before channel"), and
> ahci_xgene handles its broken edge latch the same way.  Since the
> reordering costs at most one spurious interrupt per valid one on
> conforming controllers, do it in a private interrupt handler selected for
> board_ahci_mv instead of changing libahci for everyone.
> 
> With this applied, SATA-2 and SATA-3 disks work at 3.0 Gbps on the
> 88SE6121 without the drive-side 1.5 Gbps jumper that was needed before.
> Time from link up to a successful IDENTIFY:
> 
>   WDC WD5000AADS-00S9B0  port 0    7 ms  (never identified before)
>   WDC WD3202ABYS-01B7A0  port 1   28 ms
>   WDC WD30EFRX-68EUZN0   port 1  200 ms  (3 TB, HPA detection ok)
> 
> Only the 88SE6121 was tested; board_ahci_mv also covers the 88SE6145,
> which Marvell's driver treats identically.
> 
> Link: https://lore.kernel.org/linux-ide/db6b48b7-d69a-564b-24f0-75fbd6a9e543@noerenberg.de/
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=216094
> Signed-off-by: Hajo Noerenberg <hajo-linux-ide@noerenberg.de>

Looks OK to me.

Reviewed-by: Damien Le Moal <dlemoal@kernel.org>

-- 
Damien Le Moal
Western Digital Research