Re: [PATCH] virtio-gpu: support blob alignment information

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

On Tue, Apr 01, 2025 at 01:42:03PM -0400, Sergio Lopez wrote:
> Allow the device to require certain alignment constrains for blob
> resources by extending the device configuration with the field
> "blob_alignment" and introducing the VIRTIO_GPU_F_BLOB_ALIGNMENT
> feature.
> 
> Signed-off-by: Sergio Lopez <slp@redhat.com>
> ---
>  device-types/gpu/description.tex | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/device-types/gpu/description.tex b/device-types/gpu/description.tex
> index 4435248..8e5258d 100644
> --- a/device-types/gpu/description.tex
> +++ b/device-types/gpu/description.tex
> @@ -37,6 +37,8 @@ \subsection{Feature bits}\label{sec:Device Types / GPU Device / Feature bits}
>    resources is supported.
>  \item[VIRTIO_GPU_F_CONTEXT_INIT (4)] multiple context types and
>    synchronization timelines supported.  Requires VIRTIO_GPU_F_VIRGL.
> +\item[VIRTIO_GPU_F_BLOB_ALIGNMENT (5)] configuration field
> +  \field{blob_alignment} is valid. Requires VIRTIO_GPU_F_RESOURCE_BLOB.
>  \end{description}
>  
>  \subsection{Device configuration layout}\label{sec:Device Types / GPU Device / Device configuration layout}
> @@ -52,6 +54,7 @@ \subsection{Device configuration layout}\label{sec:Device Types / GPU Device / D
>          le32 events_clear;
>          le32 num_scanouts;
>          le32 num_capsets;
> +        le32 blob_alignment;
>  };
>  \end{lstlisting}
>  
> @@ -67,6 +70,8 @@ \subsubsection{Device configuration fields}
>    supported by the device.  Minimum value is 1, maximum value is 16.
>  \item[\field{num_capsets}] specifies the maximum number of capability
>    sets supported by the device.  The minimum value is zero.
> +\item[\field{blob_alignment}] specifies the byte alignment required by
> +  the device for resource blobs.

byte alignment means no alignment restrictions.
I think "alignment, in bytes"?
I also think you mean the minimal alignment.

Also please specify the legal values, like other fields do.
Is 2G alignment always going to be sufficient, in your opinion?

>  \end{description}
>  
>  \subsubsection{Events}
> @@ -672,6 +677,9 @@ \subsubsection{Device Operation: controlq}\label{sec:Device Types / GPU Device /
>  resource. There is no restriction on the image/buffer view the driver
>  has on the blob resource.
>  
> +If VIRTIO_GPU_F_BLOB_ALIGNMENT is set, \field{size} must be aligned to
> +\field{blob_alignment} as defined in the device configuration.
> +

set where? you mean has been negotiated?

>  \item[VIRTIO_GPU_CMD_SET_SCANOUT_BLOB] sets scanout parameters for a
>     blob resource. Request data is
>    \field{struct virtio_gpu_set_scanout_blob}. Response type is
> @@ -776,6 +784,10 @@ \subsubsection{Device Operation: controlq (3d)}\label{sec:Device Types / GPU Dev
>  };
>  \end{lstlisting}
>  
> +If VIRTIO_GPU_F_BLOB_ALIGNMENT is set,

same

> \field{padding} and \field{offset}
> +must be aligned to \field{blob_alignment} as defined in the device
> +configuration.
> +
>  \item[VIRTIO_GPU_CMD_RESOURCE_UNMAP_BLOB] unmaps a
>    host-only blob resource from the host visible memory region. Request data
>    is \field{struct virtio_gpu_resource_unmap_blob}.  Response type is
> -- 
> 2.49.0