linux-kernel - Re: [PATCH v2] ata: libata-scsi: Fix get identity data failed

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Message-ID: <2a5f6751-7120-1ea8-1a1e-d401b433a34a@kernel.org>
Date:   Mon, 22 May 2023 20:47:54 +0900
From:   Damien Le Moal <dlemoal@...nel.org>
To:     John Garry <john.g.garry@...cle.com>,
        Jason Yan <yanaijie@...wei.com>,
        yangxingui <yangxingui@...wei.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com
Cc:     linux-scsi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxarm@...wei.com, prime.zeng@...ilicon.com,
        kangfenglong@...wei.com
Subject: Re: [PATCH v2] ata: libata-scsi: Fix get identity data failed

On 5/22/23 20:28, John Garry wrote:
> On 22/05/2023 09:00, Jason Yan wrote:
>>
>> OK, so the issue is that __ata_scsi_find_dev() calls ata_find_dev() with 
>> devno
>> == scsidev->id. This leads to devno being 0, 1, 2 and 3 for connected 
>> drives
> 
> This numbering comes from sas_rphy_add():
> ...
> if (identify->device_type == SAS_END_DEVICE &&
>      (identify->target_port_protocols &
>       (SAS_PROTOCOL_SSP | SAS_PROTOCOL_STP | SAS_PROTOCOL_SATA)))
> 	rphy->scsi_target_id = sas_host->next_target_id++;
> 
> ..
> 
> 	scsi_scan_target(&rphy->dev, 0, rphy->scsi_target_id, lun,
> SCSI_SCAN_INITIAL);
> }
> 
> So libata and scsi_transport_sas just use different sdev id numbering 
> schemes for host scan.
> 
>> sdd, sd1, sdf and sdg, as shown by lsscsi. However, each drive has its own
>> port+link, with the link for each one having  ata_link_max_devices() == 
>> 1, so
>> ata_find_dev() works only for the first drive with scsidev->id == 0 and 
>> fails
>> for the others. A naive fix would be this:
>>
>> diff --git a/drivers/ata/libata-scsi.c b/drivers/ata/libata-scsi.c
>> index 7bb12deab70c..e4d6f17d7ccc 100644
>> --- a/drivers/ata/libata-scsi.c
>> +++ b/drivers/ata/libata-scsi.c
>> @@ -2718,7 +2718,7 @@ static struct ata_device *__ata_scsi_find_dev(struct
>> ata_port *ap,
>>           if (!sata_pmp_attached(ap)) {
>>                   if (unlikely(scsidev->channel || scsidev->lun))
>>                           return NULL;
>> -               devno = scsidev->id;
>> +               devno = 0;
> Would this pattern work:
> 
> ata_for_each_dev(ata_dev, link, ALL) {
> 	if (ata_dev->sdev == sdev)
> 		return ata_dev;
> }

That would work too I think, even though a loop is a bit ugly...

> 
> If not, I think it's ok to have devno = 0 assignment under SAS_HOST 
> flag, even though it's far from ideal. Not both of these are not 
> preferred, then, as I mentioned before, some per-port callback to do the 
> conversion.

See the proper patch I posted a few min ago (I cc-ed you). I do not use SAS_HOST
flag :)

> 
> Thanks,
> John

-- 
Damien Le Moal
Western Digital Research