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

From: Leon Romanovsky <leon@kernel.org>
To: Parav Pandit <parav@nvidia.com>
Cc: Jason Gunthorpe <jgg@nvidia.com>,
	Doug Ledford <dledford@redhat.com>,
	"linux-rdma@vger.kernel.org" <linux-rdma@vger.kernel.org>
Subject: Re: [PATCH rdma-next] IB/mlx5: Use ib_dma APIs instead of open access to parent device
Date: Tue, 24 Nov 2020 07:20:32 +0200	[thread overview]
Message-ID: <20201124052032.GE3159@unreal> (raw)
In-Reply-To: <BY5PR12MB43226D6014DAABFD08BFBEABDCFB0@BY5PR12MB4322.namprd12.prod.outlook.com>

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.

Thanks