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Subject: Re: v5.9-rc1 commit reliably breaks pci nvme detection
To:     Christoph Hellwig <hch@infradead.org>
Cc:     "Ahmed S. Darwish" <a.darwish@linutronix.de>,
        Keith Busch <kbusch@kernel.org>,
        linux-nvme@lists.infradead.org, Sagi Grimberg <sagi@grimberg.me>,
        Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>,
        linux-kernel@vger.kernel.org
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 <83a3d1b6-1eb5-859b-3c5c-287d8d18a99b@kernel.dk>
 <20200820171214.GA15207@infradead.org>
From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <e9e4804b-f036-a1f8-63b6-b51592d9a0c5@kernel.dk>
Date:   Thu, 20 Aug 2020 11:14:55 -0600
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On 8/20/20 11:12 AM, 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.  So for the overflow to happen you need a controller that
> supports USHORT_MAX queue entries.  Which don't seem to be all that
> common.

Yeah, don't think I've ever seen those. I come across 1023 and 128 all
the time, but I don't have one in my arsenal of NVMe drives that is
any different than those two.

-- 
Jens Axboe