Re: [PATCH v5 07/14] PCI: Add driver dma ownership management

[Greg Kroah-Hartman]

On Tue, Jan 04, 2022 at 09:56:37AM +0800, Lu Baolu wrote:
> Multiple PCI devices may be placed in the same IOMMU group because
> they cannot be isolated from each other. These devices must either be
> entirely under kernel control or userspace control, never a mixture. This
> checks and sets DMA ownership during driver binding, and release the
> ownership during driver unbinding.
> 
> The device driver may set a new flag (no_kernel_api_dma) to skip calling
> iommu_device_use_dma_api() during the binding process. For instance, the
> userspace framework drivers (vfio etc.) which need to manually claim
> their own dma ownership when assigning the device to userspace.
> 
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>  include/linux/pci.h      |  5 +++++
>  drivers/pci/pci-driver.c | 21 +++++++++++++++++++++
>  2 files changed, 26 insertions(+)
> 
> diff --git a/include/linux/pci.h b/include/linux/pci.h
> index 18a75c8e615c..d29a990e3f02 100644
> --- a/include/linux/pci.h
> +++ b/include/linux/pci.h
> @@ -882,6 +882,10 @@ struct module;
>   *              created once it is bound to the driver.
>   * @driver:	Driver model structure.
>   * @dynids:	List of dynamically added device IDs.
> + * @no_kernel_api_dma: Device driver doesn't use kernel DMA API for DMA.
> + *		Drivers which don't require DMA or want to manually claim the
> + *		owner type (e.g. userspace driver frameworks) could set this
> + *		flag.

Again with the bikeshedding, but this name is a bit odd.  Of course it's
in the kernel, this is all kernel code, so you can drop that.  And
again, "negative" flags are rough.  So maybe just "prevent_dma"?

thanks,

greg k-h