Re: [PATCH v3 11/20] RDMA/core: introduce ib_dma_pci_p2p_dma_supported()

[Jason Gunthorpe]

On Thu, Sep 16, 2021 at 05:40:51PM -0600, Logan Gunthorpe wrote:
> Introduce the helper function ib_dma_pci_p2p_dma_supported() to check
> if a given ib_device can be used in P2PDMA transfers. This ensures
> the ib_device is not using virt_dma and also that the underlying
> dma_device supports P2PDMA.
> 
> Use the new helper in nvme-rdma to replace the existing check for
> ib_uses_virt_dma(). Adding the dma_pci_p2pdma_supported() check allows
> switching away from pci_p2pdma_[un]map_sg().
> 
> Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
> ---
>  drivers/nvme/target/rdma.c |  2 +-
>  include/rdma/ib_verbs.h    | 11 +++++++++++
>  2 files changed, 12 insertions(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@xxxxxxxxxx>

> +/*
> + * Check if a IB device's underlying DMA mapping supports P2PDMA transfers.
> + */
> +static inline bool ib_dma_pci_p2p_dma_supported(struct ib_device *dev)
> +{
> +	if (ib_uses_virt_dma(dev))
> +		return false;

If someone wants to make rxe/hfi/qib use this stuff then they will
have to teach the the driver to do all the p2p checks and add some
struct ib_device flag

Jason