Re: [PATCH v2] content: Reserve ID 52 for QPSFI device

["Michael S. Tsirkin" <mst@redhat.com>]

On Thu, Oct 22, 2026 at 03:07:41AM -0400, Demi Marie Obenour wrote:
> On 10/22/26 00:35, Cornelia Huck wrote:
> > On Wed, Oct 21 2026, "Michael S. Tsirkin" <mst@redhat.com> wrote:
> > 
> >> On Wed, Oct 21, 2026 at 03:25:31PM -0400, Demi Marie Obenour wrote:
> >>> On 10/21/26 14:00, Peter Hilber wrote:
> >>>> Reserve a device ID for QPSFI devices (Qualcomm Platform Subsystem
> >>>> Firmware Interface). QPSFI devices expose functionality across SoC
> >>>> subsystems through a common Virtio-based protocol. There are no plans to
> >>>> standardize the devices.
> >>>>
> >>>> The Linux DCP display driver series is planned as the first user of this
> >>>> device ID:
> >>>>
> >>>> https://lore.kernel.org/all/20261015-jshekhar-drm-msm-dcp-v1-v1-10-48aad0fe4f72@oss.qualcomm.com/
> >>>>
> >>>> Device ID 51 is already reserved for the Virtio HAB device:
> >>>>
> >>>> https://lore.kernel.org/virtio-comment/20260702140939.3535968-1-zeloren@qti.qualcomm.com/
> >>>>
> >>>> Signed-off-by: Peter Hilber <peter.hilber@oss.qualcomm.com>
> >>>> ---
> >>>>
> >>>>     v2:
> >>>>     
> >>>>     - Rename the device from "Snapdragon device" to "QPSFI device".
> >>>>     
> >>>>     - Refer to DCP Linux driver patch as planned first QPSFI user.
> >>>>     
> >>>>     v1:
> >>>>     
> >>>>     - Was posted as "content: Reserve ID 52 for Snapdragon device":
> >>>>     
> >>>>       https://lore.kernel.org/virtio-comment/20260826115504.1955-1-peter.hilber@oss.qualcomm.com/
> >>>>
> >>>>  content.tex | 2 ++
> >>>>  1 file changed, 2 insertions(+)
> >>>>
> >>>> diff --git a/content.tex b/content.tex
> >>>> index 243ce2dde36b..7416939e67d3 100644
> >>>> --- a/content.tex
> >>>> +++ b/content.tex
> >>>> @@ -805,6 +805,8 @@ \chapter{Device Types}\label{sec:Device Types}
> >>>>  \hline
> >>>>  50         &   Video encoder/decoder device \\
> >>>>  \hline
> >>>> +52         &   QPSFI device \\
> >>>> +\hline
> >>>>  \end{longtable}
> >>>>  
> >>>>  Some of the devices above are unspecified by this document,
> >>>
> >>> I think it would be best to have a single ID for vendor-specific devices.
> >>> I believe most of the ID space has already been used, at least for virtio-PCI.
> >>> -- 
> >>> Sincerely,
> >>> Demi Marie Obenour (she/her/hers)
> >>
> >> Sounds like a good idea to me. And then qualcomm can do what they
> >> want, like check subsystem id for pci or whatever?
> >> Only issue is there is no way to distinguish for mmio/ccw.
> >> Maybe, add vendor specific id as first e.g. 8 bytes ro in the config space?
> >> Peter?
> > 
> > Using some information in the config space looks like the most flexible
> > way to me. Are we still happy with how the device ids are organized in
> > general (i.e. when do we want a new one, and when do we want to extend
> > an existing device?)
> 
> For a platform device like this, I'd prefer to pass the information out
> of band.  After all, this device will only ever be found on Qualcomm
> SoCs, and presumably the kernel knows exactly which PCI device is
> supposed to be the QPSFI device.  This means that the kernel can just
> special-case it.

Yes but we are discussing making this id a general "vendor specific
device", as opposed to a "qualcomm device".
Could you share, e.g. if this device has config space, and whether
reading X bytes at offset 0 of this device is harmless, for some value
of X?

> Would it make sense to put this in the ACPI tables or device tree?

As long as it's vendor specific.

> -- 
> Sincerely,
> Demi Marie Obenour (she/her/hers)