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Re: [PATCH 17/17] hw/block/nvme: change controller pci id


From: Klaus Jensen
Subject: Re: [PATCH 17/17] hw/block/nvme: change controller pci id
Date: Mon, 7 Sep 2020 11:20:52 +0200

On Sep  7 10:58, Klaus Jensen wrote:
> On Sep  7 10:36, Philippe Mathieu-Daudé wrote:
> > On 9/7/20 9:23 AM, Klaus Jensen wrote:
> > > On Sep  7 04:28, Philippe Mathieu-Daudé wrote:
> > >> +David in case
> > >>
> > >> On 9/4/20 4:19 PM, Klaus Jensen wrote:
> > >>> From: Klaus Jensen <k.jensen@samsung.com>
> > >>>
> > >>> There are two reasons for changing this:
> > >>>
> > >>>   1. The nvme device currently uses an internal Intel device id.
> > >>>
> > >>>   2. Since commits "nvme: fix write zeroes offset and count" and "nvme:
> > >>>      support multiple namespaces" the controller device no longer has
> > >>>      the quirks that the Linux kernel think it has.
> > >>>
> > >>>      As the quirks are applied based on pci vendor and device id, change
> > >>>      them to get rid of the quirks.
> > >>>
> > >>> To keep backward compatibility, add a new 'x-use-intel-id' parameter to
> > >>> the nvme device to force use of the Intel vendor and device id. This is
> > >>> off by default but add a compat property to set this for 5.1 machines
> > >>> and older.
> > >>
> > >> So now what happens if you start a 5.1 machine with a recent kernel?
> > >> Simply the kernel will use unnecessary quirks, or are there more
> > >> changes in behavior?
> > >>
> > > 
> > > Yes, the kernel will then just apply unneccesary quirks, these are:
> > > 
> > >   1. NVME_QUIRK_IDENTIFY_CNS which says that the device does not support
> > >      anything else than values 0x0 and 0x1 for CNS (Identify Namespace and
> > >      Identify Namespace). With multiple namespace support, this just
> > >      means that the kernel will "scan" namespaces instead of using
> > >      "Active Namespace ID list" (CNS 0x2).
> > > 
> > >   2. NVME_QUIRK_DISABLE_WRITE_ZEROES. The nvme device started out with a
> > >      broken Write Zeroes implementation which has since been fixed in
> > >      commit 9d6459d21a6e ("nvme: fix write zeroes offset and count").
> > 
> > OK thanks. Can you amend that information in the commit
> > description please?
> > 
> 
> Yes, absolutely.

By the way. Is it correct use of an 'x-' parameter here - since it is
something that we might remove in the future? I was unable to find any
documentation on the purpose of the 'x-' prefix, but I was guessing it
was for stuff like this.

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