[virtio-dev] Re: [PATCH 07/11] transport-pci: Introduce transitional MMR device id

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

On Fri, Mar 31, 2023 at 01:58:30AM +0300, Parav Pandit wrote:
> Transitional MMR device PCI Device IDs are unique. Hence,
> any of the existing drivers do not bind to it.
> This further maintains the backward compatibility with
> existing drivers.
> 
> Co-developed-by: Satananda Burla <sburla@marvell.com>
> Signed-off-by: Parav Pandit <parav@nvidia.com>

This is IMO just too big a change: fundamentally this is a completely
new transport since no existing drivers can use this device at all. Not
a thing we should do lightly. And we have options on the table
such as AQ, which address most of the issue. Yes they do not
work for passthrough of a PF but that seems like a minor issue.
If we want to save the MMR idea, let's find a way to cut
down this patchset's size significantly.


On a more positive side, I do not really see a reason to
have a new ID at all. Device can have a normal device ID
and additionally the new capability.









> ---
>  transport-pci.tex | 45 +++++++++++++++++++++++++++++++++++++++++----
>  1 file changed, 41 insertions(+), 4 deletions(-)
> 
> diff --git a/transport-pci.tex b/transport-pci.tex
> index ee11ba5..665448e 100644
> --- a/transport-pci.tex
> +++ b/transport-pci.tex
> @@ -19,12 +19,14 @@ \section{Virtio Over PCI Bus}\label{sec:Virtio Transport Options / Virtio Over P
>  \subsection{PCI Device Discovery}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Discovery}
>  
>  Any PCI device with PCI Vendor ID 0x1af4, and PCI Device ID 0x1000 through
> -0x107f inclusive is a virtio device. The actual value within this range
> -indicates which virtio device is supported by the device.
> +0x107f inclusive and DeviceID 0x10f9 through 0x10ff is a virtio device.
> +The actual value within this range indicates which virtio device
> +type it is.
>  The PCI Device ID is calculated by adding 0x1040 to the Virtio Device ID,
>  as indicated in section \ref{sec:Device Types}.
> -Additionally, devices MAY utilize a Transitional PCI Device ID range,
> -0x1000 to 0x103f depending on the device type.
> +Additionally, devices MAY utilize a Transitional PCI Device ID range
> +0x1000 to 0x103f inclusive or a Transitional MMR PCI Device ID range
> +0x10f9 to 0x10ff inclusive, depending on the device type.
>  
>  \devicenormative{\subsubsection}{PCI Device Discovery}{Virtio Transport Options / Virtio Over PCI Bus / PCI Device Discovery}
>  
> @@ -95,6 +97,41 @@ \subsubsection{Legacy Interfaces: A Note on PCI Device Discovery}\label{sec:Virt
>  
>  This is to match legacy drivers.
>  
> +\subsubsection{Transitional MMR Interface: A Note on PCI Device
> +Discovery}\label{sec:Virtio Transport Options / Virtio Over PCI
> +Bus / PCI Device Discovery / Transitional MMR Interface: A Note on PCI Device Discovery}
> +
> +The transitional MMR device has one of the following PCI Device ID
> +depending on the device type:
> +
> +\begin{tabular}{|l|c|}
> +\hline
> +Transitional PCI Device ID  &  Virtio Device    \\
> +\hline \hline
> +0x10f9      &   network device     \\
> +\hline
> +0x10fa     &   block device     \\
> +\hline
> +0x10fb     & memory ballooning (traditional)  \\
> +\hline
> +0x10fc     &      console       \\
> +\hline
> +0x10fd     &     SCSI host      \\
> +\hline
> +0x10fe     &  entropy source    \\
> +\hline
> +0x10ff     &   9P transport     \\
> +\hline
> +\end{tabular}
> +
> +The PCI Subsystem Vendor ID and the PCI Subsystem Device ID MAY
> +reflect the PCI Vendor and Device ID of the environment.
> +
> +The transitional MMR driver MUST match any PCI Revision ID value.
> +
> +The transitional MMR driver MAY match any PCI Subsystem Vendor ID and
> +any PCI Subsystem Device ID value.
> +
>  \subsection{PCI Device Layout}\label{sec:Virtio Transport Options / Virtio Over PCI Bus / PCI Device Layout}
>  
>  The device is configured via I/O and/or memory regions (though see
> -- 
> 2.26.2


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