linux-kernel - Re: [PATCH] nvme: determine the number of IO queues

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Message-ID: <a2f0a97e14b884dc1183db9cbdd6f4b520000ce3.camel@redhat.com>
Date:   Wed, 17 Apr 2019 20:32:04 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     Aaron Ma <aaron.ma@...onical.com>, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org, keith.busch@...el.com, axboe@...com
Subject: Re: [PATCH] nvme: determine the number of IO queues

On Wed, 2019-04-17 at 22:12 +0800, Aaron Ma wrote:
> Some controllers support limited IO queues, when over set
> the number, it will return invalid field error.
> Then NVME will be removed by driver.
> 
> Find the max number of IO queues that controller supports.
> When it still got invalid result, set 1 IO queue at least to
> bring NVME online.

To be honest a spec compliant device should not need this.
The spec states:

"Number of I/O Completion Queues Requested (NCQR): Indicates the number of I/O
Completion
Queues requested by software. This number does not include the Admin Completion
Queue. A
minimum of one queue shall be requested, reflecting that the minimum support is
for one I/O
Completion Queue. This is a 0’s based value. The maximum value that may be
specified is 65,534
(i.e., 65,535 I/O Completion Queues). If the value specified is 65,535, the
controller should return
an error of Invalid Field in Command."

This implies that you can ask for any value and the controller must not respond
with an error, but rather indicate how many queues it supports.

Maybe its better to add a quirk for the broken device, which needs this?

Best regards,
	Maxim Levitsky