linux-kernel - Re: [PATCH RFC 0/6] libata/scsi/libsas: Allocate SCSI device earlier for ata port probe

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Message-ID: <40b9e090-5ba3-1191-4fe9-80467284ae72@opensource.wdc.com>
Date:   Wed, 21 Sep 2022 13:04:51 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     John Garry <john.garry@...wei.com>, jejb@...ux.ibm.com,
        martin.petersen@...cle.com, hare@...e.de, hch@....de
Cc:     linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-scsi@...r.kernel.org, brking@...ibm.com
Subject: Re: [PATCH RFC 0/6] libata/scsi/libsas: Allocate SCSI device earlier
 for ata port probe

On 9/20/22 19:27, John Garry wrote:
> Currently for libata the SCSI device (sdev) associated with an ata_device
> is allocated when the port probe has completed.
> 
> It's useful to have the SCSI device and its associated request queue
> available earlier for the port probe. Specifically if we have the
> request queue available, then we can:
> - Easily put ATA qc in SCSI cmnd priv data
> - Send ATA internal commands on SCSI device request queue for [0]. The
>    current solution there is to use the shost sdev request queue, which
>    isn't great.
>    
> This series changes the ata port probe to alloc the sdev in the
> ata_device revalidation, and then just do a SCSI starget scan afterwards.
> 
> Why an RFC?
> 1. IPR  driver needs to be fixed up - it does not use ATA EH port probe
>     Mail [1] needs following up

Yes. If IPR could be converted to ata error_handler, a lot of code can 
be simplified in libata too.

> 2. SATA PMP support needs verification, but I don't have a setup

Port multiplier behind a sas HBA will be challenging to setup :)
I can try, but I will need to open up one of my servers and hook a small 
PMP box to one of the pm8001 plugs. I may have the cables for that... 
Let me check.

> 3. This series needs to be merged into or go after [0]
> 
> Patch 1/6 could be merged now.
> 
> [0] https://lore.kernel.org/linux-ide/1654770559-101375-1-git-send-email-john.garry@huawei.com/
> [1] https://lore.kernel.org/linux-ide/369448ed-f89a-c2db-1850-91450d8b5998@opensource.wdc.com/
> 
> Any comments welcome - please have a look.
> 
> Based on v6.0-rc4 and tested for QEMU AHCI and libsas.
> 
> John Garry (6):
>    scsi: core: Use SCSI_SCAN_RESCAN in  __scsi_add_device()
>    scsi: scsi_transport_sas: Allocate end device target id in the rphy
>      alloc
>    scsi: core: Add scsi_get_dev()
>    ata: libata-scsi: Add ata_scsi_setup_sdev()
>    scsi: libsas: Add sas_ata_setup_device()
>    ata: libata-scsi: Allocate sdev early in port probe
> 
>   drivers/ata/libata-eh.c           |  4 +++
>   drivers/ata/libata-scsi.c         | 45 +++++++++++++++++++++----------
>   drivers/ata/libata.h              |  1 +
>   drivers/scsi/libsas/sas_ata.c     | 20 ++++++++++++++
>   drivers/scsi/scsi_scan.c          | 28 ++++++++++++++++++-
>   drivers/scsi/scsi_transport_sas.c | 25 +++++++++++------
>   include/linux/libata.h            |  2 ++
>   include/scsi/scsi_host.h          |  3 +++
>   8 files changed, 105 insertions(+), 23 deletions(-)
> 

-- 
Damien Le Moal
Western Digital Research