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From:   John Garry <john.garry@huawei.com>
Subject: Re: v5.9-rc1 commit reliably breaks pci nvme detection
To:     Christoph Hellwig <hch@infradead.org>, Jens Axboe <axboe@kernel.dk>
CC:     Sagi Grimberg <sagi@grimberg.me>,
        Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>,
        <linux-kernel@vger.kernel.org>, <linux-nvme@lists.infradead.org>,
        "Ahmed S. Darwish" <a.darwish@linutronix.de>,
        Keith Busch <kbusch@kernel.org>
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Message-ID: <cd34f822-3f9d-80d1-f656-24f8cdeae42d@huawei.com>
Date:   Fri, 21 Aug 2020 08:28:03 +0100
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On 20/08/2020 18:12, Christoph Hellwig wrote:
> On Thu, Aug 20, 2020 at 11:10:58AM -0600, Jens Axboe wrote:
>> To be fair, I've only heard this one complaint about it, so hopefully it's
>> not too widespread. I'm on an x86-64 laptop myself with nvme, and it works
>> just fine:-)
> The cause for this is the weird NVMe of by ones, where 0 in a field
> means 1.

I thought that this was a common trick by spec writers to fit a number 
in range (0, 2^x] in x bits (as opposed to x+1).