Re: [PATCH 1/2] nvme-apple: Only limit admin queue tag space when with Linear SQ is present

[Nick Chan <towinchenmi@gmail.com>]

Christoph Hellwig 於 2026/6/10 下午1:11 寫道:
> On Sat, Jun 06, 2026 at 09:25:25PM +0800, Nick Chan wrote:
>> Apple NVMe controllers require tags of pending commands to not be shared
>> across admin and IO queues. However, on Apple A11 without linear SQ, it is
>> not possible for either queue to skip over some tags and must go from 0 to
>> the configured maximum before wrapping around.
>>
>> As a result, in order to prevent tag collision, dynamic tag reservation
>> while a command is in-flight becomes necessary. In this context, there is
>> no reason to limit the admin queue's tag space, as it is not helpful in
>> preventing tag collision.
> I'm not really into these Apple specific, but what does
> "dynamic tag reservation" mean here?

This version is based on an incorrect premise (v2 is correct and already applied)
so feel free to stop reading.

In this version, the incorrect premise is that it was not possible for either queue
to skip over tags and must go from 0 to the configured the maximum. 

Under this premise, the only way to prevent collision is to set a bitfield indicating
which tags are in use when submitting a command ("dynamic tag reservation").
If a tag is already found to be used when submitting a command, return
BLK_STS_RESOURCE so the caller retries later.

Best regards,
Nick Chan



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