linux-kernel - Re: [PATCH 3/3] cnic,bnx2,bnx2x: use UIO_MEM_DMA

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Message-ID: <ZRhmqBRNUB3AfLv/@rhel-developer-toolbox>
Date:   Sat, 30 Sep 2023 11:19:20 -0700
From:   Chris Leech <cleech@...hat.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Christoph Hellwig <hch@....de>, Rasesh Mody <rmody@...vell.com>,
        Ariel Elior <aelior@...vell.com>,
        Sudarsana Kalluru <skalluru@...vell.com>,
        Manish Chopra <manishc@...vell.com>,
        Nilesh Javali <njavali@...vell.com>,
        Manish Rangankar <mrangankar@...vell.com>,
        Jerry Snitselaar <jsnitsel@...hat.com>,
        John Meneghini <jmeneghi@...hat.com>,
        Lee Duncan <lduncan@...e.com>,
        Mike Christie <michael.christie@...cle.com>,
        Hannes Reinecke <hare@...nel.org>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] cnic,bnx2,bnx2x: use UIO_MEM_DMA_COHERENT

On Sat, Sep 30, 2023 at 09:06:51AM +0200, Greg Kroah-Hartman wrote:
> On Fri, Sep 29, 2023 at 10:00:23AM -0700, Chris Leech wrote:
> > Make use of the new UIO_MEM_DMA_COHERENT type to properly handle mmap
> > for dma_alloc_coherent buffers.
> 
> Why are ethernet drivers messing around with UIO devices?  That's not
> what UIO is for, unless you are trying to do kernel bypass for these
> devices without anyone noticing?
> 
> confused,

It's confusing. The bnx2 driver stack included a cnic (converged nic?)
module that sits between the ethernet drivers (bnx2, bnx2x) and protocol
offload drivers (iscsi, fcoe, rdma).

The iscsi module (bnx2i) uses a passthrough interface from cnic to
handle some network configuration that the device firmware doesn't do.
It uses a uio device and a userspace component called iscsiuio to do
that.

Questions beyond that will probably need to be answer by one of the many
Marvell engineers copied on this thread.

- Chris