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Message-ID: <0ae5000d-8e9a-da0f-b470-9f87f1b5e290@huawei.com>
Date:   Wed, 21 Sep 2022 09:24:02 +0100
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Subject: Re: [PATCH RFC 0/6] libata/scsi/libsas: Allocate SCSI device earlier
 for ata port probe
To:     Damien Le Moal <damien.lemoal@opensource.wdc.com>,
        <jejb@linux.ibm.com>, <martin.petersen@oracle.com>, <hare@suse.de>,
        <hch@lst.de>
CC:     <linux-ide@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
        <linux-scsi@vger.kernel.org>, <brking@us.ibm.com>
References: <1663669630-21333-1-git-send-email-john.garry@huawei.com>
 <40b9e090-5ba3-1191-4fe9-80467284ae72@opensource.wdc.com>
From:   John Garry <john.garry@huawei.com>
In-Reply-To: <40b9e090-5ba3-1191-4fe9-80467284ae72@opensource.wdc.com>
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On 21/09/2022 05:04, Damien Le Moal wrote:
> 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.

Hmmm... yeah, it would be good to see progress there.

> 
>> 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.

I was more thinking of just AHCI with a port multiplier.

As for SAS controllers, I don't think it's something to be concerned 
about. For a start, I know for sure that hisi_sas HW does not support 
port multipliers, and I don't think that pm8001 does either. In 
addition, libsas does not even support it - I did see a series in the 
scsi list from years ago (to support it), but it did not progress.

Thanks,
John