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Date:   Thu, 2 May 2019 06:57:23 -0600
From:   Keith Busch <keith.busch@intel.com>
To:     Akinobu Mita <akinobu.mita@gmail.com>
Cc:     linux-nvme@lists.infradead.org, linux-kernel@vger.kernel.org,
        Johannes Berg <johannes@sipsolutions.net>,
        Jens Axboe <axboe@fb.com>, Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>
Subject: Re: [PATCH 0/4] nvme-pci: support device coredump
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On Thu, May 02, 2019 at 05:59:17PM +0900, Akinobu Mita wrote:
> This enables to capture snapshot of controller information via device
> coredump machanism, and it helps diagnose and debug issues.
> 
> The nvme device coredump is triggered before resetting the controller
> caused by I/O timeout, and creates the following coredump files.
> 
> - regs: NVMe controller registers, including each I/O queue doorbell
>         registers, in nvme-show-regs style text format.

You're supposed to treat queue doorbells as write-only. Spec says:

  The host should not read the doorbell registers. If a doorbell register
  is read, the value returned is vendor specific.