Apple NVMe controllers require tags of pending commands to not be shared
across admin and IO queues.

If a pending command tag is duplicated across queues, the firmware
crashes with: "duplicate tag error for tag N", with N being the tag.

On Apple M1 or above, this is worked around by partitioning the tag
space between the admin and IO queue.

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.

Instead of partitioning the tag space, which is not possible without
linear SQ, prevent tag collisions by keeping track of which tags are
currently in-flight across either queues, and return BLK_STS_RESOURCE to
temporaily block command submission when a collision would have occured.

While fixing the issue, it became apparent the admin queue tag space
is limited even on Apple A11. There is no reason to do this as it hampers
performance and does not help preventing tag collisions, so also allow
the admin queue to use the full tag space.

Tested on iPhone 8, iPhone X and Macbook Pro (14-inch, M1 Pro, 2021).

Signed-off-by: Nick Chan <towinchenmi@gmail.com>
---
Nick Chan (1):
      nvme-apple: Only limit admin queue tag space when with Linear SQ is present

Yuriy Havrylyuk (1):
      nvme-apple: Prevent tag collision across queues even if tag space is shared

 drivers/nvme/host/apple.c | 70 ++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 69 insertions(+), 1 deletion(-)
---
base-commit: e43ffb69e0438cddd72aaa30898b4dc446f664f8
change-id: 20260606-prevent-tag-collision-t8015-1c8adb3234de

Best regards,
-- 
Nick Chan <towinchenmi@gmail.com>