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

[Klaus Jensen]

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").

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