Re: [Regression] commit 8a4aeec8d(libata/ahci: accommodate tag ordered controllers)

[Ming Lei]

Hi Tejun,

On Thu, Jun 5, 2014 at 9:41 PM, Tejun Heo <tj@xxxxxxxxxx> wrote:
> Hello,
>
> (cc'ing ahci_xgene folks)
>
> On Thu, Jun 05, 2014 at 09:24:04PM +0800, Ming Lei wrote:
>> On Thu, Jun 5, 2014 at 9:12 PM, Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
>> > On Thu, Jun 5, 2014 at 1:53 AM, Ming Lei <ming.lei@xxxxxxxxxxxxx> wrote:
>> >> Hi Dan and Tejun,
>> >>
>> >> Looks the commit 8a4aeec8d(libata/ahci: accommodate tag ordered
>> >> controllers) causes below sata failure[1] on APM AHCI controller.
>> >>
>> >> And the error does disappear after reverting the commit.
>> >
>> > Can you give some more details about the workload and the disk?  What
>> > is the APM AHCI?
>>
>> The commit causes the APM arm64 based system not bootable, and not
>> special workload, just when mounting rootfs or reading init files.
>>
>> APM AHCI:
>>       drivers/ata/ahci_xgene.c
>
> Urgh... so, the controller can't handle tags allocated in round-robin
> instead of lowest-first?  Ming, can you please test with different
> controllers / disks / ssds and see whether the problem stays with the
> controller?  Loc, can you guys please look into it so that at least
> the next revision hardware can fix the issue?

The problem has been observed on several apm arm64 boards
with different disks.

>
> Provided that the tag allocation itself isn't broken, which isn't too
> likely given the lack of bug reports on other controllers, we'll need
> to blacklist ahci_xgene somehow.  Either disable NCQ support on it or
> implement an alternative lowest-first tag allocation for it.  If this
> actually is the controller freaking out about tags allocated in a
> different order, I'm not sure how much confidence we can put in its
> NCQ implementation tho and it might be a better idea to simply plug
> NCQ support on it until we understand the details of the problem.
>
> So, something like the following?  Ming, can you please verify whether
> the following makes the machine boot again?

Looks the problem still persists after applying your patch of disabling
NCQ.

>
> Thanks.
>
> diff --git a/drivers/ata/ahci_xgene.c b/drivers/ata/ahci_xgene.c
> index 77c89bf..4950600 100644
> --- a/drivers/ata/ahci_xgene.c
> +++ b/drivers/ata/ahci_xgene.c
> @@ -302,9 +302,16 @@ static struct ata_port_operations xgene_ahci_ops = {
>         .read_id = xgene_ahci_read_id,
>  };
>
> +/*
> + * The controller seems to freak out depending on the order of tag
> + * allocation.  NCQ support is disabled until the problem is better
> + * understood.
> + *
> + * http://lkml.kernel.org/g/CACVXFVMnM6w5ZLX=S8fJHeVoEqxH2JG3Wg=GPMeoVnOpAjsvAA@xxxxxxxxxxxxxx
> + */
>  static const struct ata_port_info xgene_ahci_port_info = {
> -       AHCI_HFLAGS(AHCI_HFLAG_NO_PMP | AHCI_HFLAG_YES_NCQ),
> -       .flags = AHCI_FLAG_COMMON | ATA_FLAG_NCQ,
> +       AHCI_HFLAGS(AHCI_HFLAG_NO_PMP),
> +       .flags = AHCI_FLAG_COMMON,
>         .pio_mask = ATA_PIO4,
>         .udma_mask = ATA_UDMA6,
>         .port_ops = &xgene_ahci_ops,

Thanks,
--
Ming Lei
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