From: John Garry <john.g.garry@oracle.com>
To: Hannes Reinecke <hare@suse.de>,
Damien Le Moal <damien.lemoal@opensource.wdc.com>,
John Garry <john.garry@huawei.com>,
axboe@kernel.dk, jejb@linux.ibm.com, martin.petersen@oracle.com,
jinpu.wang@cloud.ionos.com, bvanassche@acm.org, hch@lst.de,
ming.lei@redhat.com, niklas.cassel@wdc.com
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-ide@vger.kernel.org, linux-scsi@vger.kernel.org,
linuxarm@huawei.com
Subject: Re: [PATCH RFC v3 16/22] ata: libata-scsi: Allocate sdev early in port probe
Date: Mon, 7 Nov 2022 10:09:55 +0000 [thread overview]
Message-ID: <59947ba8-d1a1-2e50-6199-f3974221f8fb@oracle.com> (raw)
In-Reply-To: <331fffd7-b5db-9b4a-42ae-940a6b54a37f@suse.de>
>>>>> @@ -4289,26 +4294,16 @@ void ata_scsi_scan_host(struct ata_port
>>>>> *ap, int sync)
>>>>> repeat:
I've been trying to follow this thread, below, but got a bit lost ....
>>>>> ata_for_each_link(link, ap, EDGE) {
>>>>> ata_for_each_dev(dev, link, ENABLED) {
>>>>> - struct scsi_device *sdev;
>>>>> + struct Scsi_Host *shost = ap->scsi_host;
>>>>> int channel = 0, id = 0;
>>>>> - if (dev->sdev)
>>>>> - continue;
>>>>> -
>>>>> if (ata_is_host_link(link))
>>>>> id = dev->devno;
>>>>> else
>>>>> channel = link->pmp;
>>>>> - sdev = __scsi_add_device(ap->scsi_host, channel,
>>>>> id, 0,
>>>>> - NULL);
>>>>> - if (!IS_ERR(sdev)) {
>>>>> - dev->sdev = sdev;
>>>>> - ata_scsi_assign_ofnode(dev, ap);
>>>>
>>>> Is there something equivalent to what this function does inside
>>>> scsi_scan_target() ? I had a quick look but did not see anything...
>>>>
So are we discussing below whether we can have fixed channel, id, lun
per ATA sdev per shost? If so, I don't think it would work as libsas
uses dynamic target ids per host.
>>> Typically, the SCSI layer has two ways of scanning.
>>> One it the old-style serial scanning (originating in the old SCSI
>>> parallel model):
>>> The scanning code will blindly scan _all_ devices up to max_luns, and
>>> attach every device for which the scanning code returns 'OK'.
>>> The other one is to issue REPORT_LUNS and scan all LUNs returned there.
>>>
>>> Mapped to libata we would need to figure out a stable SCSI enumeration,
>>> given that we have PMP and slave devices to content with.
>>> To my knowledge we have ATA ports, each can have either a 'master' and
>>> 'slave' device, _or_ it be a PMP port when it can support up to 16
>>> devices, right?
>>
>> yes
>>
>>> Point being, master/slave and PMP are exclusive, right?
>>
>> Never heard of pmp with ide cable :)
>>
> See?
>
>>> So we can make the master as LUN 0, and the slave as LUN 1.
>>
>> Yes, but isn't that a little wrong ? That would assume that the ata port
>> is the device and the ata devices the luns of that device. But beside
>> the "link busy" stuff that needs to be dealt with, master and slave are
>> independent devices, unlike LUNs. No ?
>> Well; technically, yes.
>
> But we already enumerate the ata ports (which is typically done by the
> hardware/PCI layer etc), and if we were try to model slave devices as
> independent ports we would either have to insert a numbering (awkward)
> or add a number at the en (even more awkward).
>
> And the one key takeaway from the 'multiple actuators' discussion is
> that LUNs _are_ independent (cf all the hoops they had to jump through
> to define a command spanning several LUNs ...)(which, incidentally, we
> could leverage here, too ...), and the target port really only serves as
> an enumeration thingie to address the LUNs.
>
> So we _could_ map the master device on LUN 0 and the slave device on LUN
> 1 with no loss of functionality, _but_ enable a consistent SCSI enumeration
Thanks,
John
next prev parent reply other threads:[~2022-11-07 10:10 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-25 10:17 [PATCH RFC v3 00/22] blk-mq/libata/scsi: SCSI driver tagging improvements Part I John Garry
2022-10-25 10:11 ` John Garry
2022-10-25 10:17 ` [PATCH RFC v3 01/22] blk-mq: Don't get budget for reserved requests John Garry
2022-10-27 1:16 ` Damien Le Moal
2022-10-27 9:09 ` John Garry
2022-10-25 10:17 ` [PATCH RFC v3 02/22] scsi: core: Add scsi_get_dev() John Garry
2022-10-25 10:17 ` [PATCH RFC v3 03/22] scsi: core: Implement reserved command handling John Garry
2022-10-27 1:18 ` Damien Le Moal
2022-10-27 7:51 ` Hannes Reinecke
2022-10-27 8:16 ` John Garry
2022-10-27 9:11 ` John Garry
2022-10-25 10:17 ` [PATCH RFC v3 04/22] scsi: core: Add support to send reserved commands John Garry
2022-10-27 1:21 ` Damien Le Moal
2022-10-27 9:13 ` John Garry
2022-10-27 9:18 ` Damien Le Moal
2022-10-25 10:17 ` [PATCH RFC v3 05/22] scsi: core: Add support for reserved command timeout handling John Garry
2022-10-25 10:18 ` [PATCH RFC v3 06/22] scsi: libsas: Improve sas_ex_discover_expander() error handling John Garry
2022-10-25 10:18 ` [PATCH RFC v3 07/22] scsi: libsas: Notify LLDD expander found before calling sas_rphy_add() John Garry
2022-10-25 10:18 ` [PATCH RFC v3 08/22] scsi: scsi_transport_sas: Alloc sdev for expander John Garry
2022-10-25 10:18 ` [PATCH RFC v3 09/22] scsi: libsas: Add sas_alloc_slow_task_rq() John Garry
2022-10-25 10:18 ` [PATCH RFC v3 10/22] scsi: libsas: Add sas_queuecommand_internal() John Garry
2022-10-25 10:18 ` [PATCH RFC v3 11/22] scsi: libsas: Add sas_internal_timeout() John Garry
2022-10-25 10:18 ` [PATCH RFC v3 12/22] scsi: core: Use SCSI_SCAN_RESCAN in __scsi_add_device() John Garry
2022-10-25 10:18 ` [PATCH RFC v3 13/22] scsi: scsi_transport_sas: Allocate end device target id in the rphy alloc John Garry
2022-10-25 10:18 ` [PATCH RFC v3 14/22] ata: libata-scsi: Add ata_scsi_setup_sdev() John Garry
2022-10-25 10:18 ` [PATCH RFC v3 15/22] scsi: libsas: Add sas_ata_setup_device() John Garry
2022-10-25 10:18 ` [PATCH RFC v3 16/22] ata: libata-scsi: Allocate sdev early in port probe John Garry
2022-10-27 1:34 ` Damien Le Moal
2022-10-27 8:11 ` Hannes Reinecke
2022-10-27 9:16 ` Damien Le Moal
2022-10-27 9:51 ` Hannes Reinecke
2022-11-07 10:09 ` John Garry [this message]
2022-11-07 10:20 ` Hannes Reinecke
2022-10-25 10:18 ` [PATCH RFC v3 17/22] scsi: libsas drivers: Reserve tags John Garry
2022-10-25 10:18 ` [PATCH RFC v3 18/22] scsi: libsas: Queue SMP commands as requests John Garry
2022-10-27 1:36 ` Damien Le Moal
2022-10-27 10:45 ` John Garry
2022-10-25 10:18 ` [PATCH RFC v3 19/22] scsi: libsas: Queue TMF " John Garry
2022-10-25 10:18 ` [PATCH RFC v3 20/22] scsi: core: Add scsi_alloc_request_hwq() John Garry
2022-10-25 10:18 ` [PATCH RFC v3 21/22] scsi: libsas: Queue internal abort commands as requests John Garry
2022-10-29 1:15 ` chenxiang (M)
2022-11-02 10:04 ` John Garry
2022-11-03 3:09 ` chenxiang (M)
2022-10-25 10:18 ` [PATCH RFC v3 22/22] scsi: libsas: Delete sas_task_slow.timer John Garry
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