Re: [PATCH rdma-next] IB/mlx5: Use ib_dma APIs instead of open access to parent device

[Jason Gunthorpe <jgg@nvidia.com>]

On Tue, Nov 24, 2020 at 07:20:32AM +0200, Leon Romanovsky wrote:
> On Tue, Nov 24, 2020 at 03:34:56AM +0000, Parav Pandit wrote:
> >
> >
> > > From: Jason Gunthorpe <jgg@nvidia.com>
> > > Sent: Monday, November 23, 2020 7:30 PM
> > >
> > > On Mon, Nov 23, 2020 at 10:24:00AM +0200, Leon Romanovsky wrote:
> > > > From: Parav Pandit <parav@nvidia.com>
> > > >
> > > > DMA operation of the IB device is done using ib_device->dma_device.
> > > > This is well abstracted using ib_dma APIs.
> > > >
> > > > Hence, instead of doing open access to parent device, use IB core
> > > > provided dma mapping APIs.
> > >
> > > Why?
> > >
> > > The ib DMA APIs are for people using verbs, they are only needed to pack things
> > > into the ib_sge
> > >
> > > If you are inside a driver, not using the verbs API, or not using ib_sge, then you
> > > should not be using the ib_dma API
> > >
> > Thanks for clarifying this. Using ib_dma apis make the code clear for dma device access clear and explicit.
> >
> > > It is an abberation, we should minimize its use.
> > Alright. In that case will use the pci_dev as mlx5 driver internally has the knowledge of it and avoid using ib_dma APIs.
> 
> Yeah, let's do v2, although I don't understand the purpose of ib_dma
> helpers if ib drivers can't use it.

They are for ULPs, not drivers. Drivers are supposed to know how they
are doing dma mapping already

Jason