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Message-ID: <2023100114-flatware-mourner-3fed@gregkh> Date: Sun, 1 Oct 2023 13:57:25 +0200 From: Greg Kroah-Hartman <gregkh@...uxfoundation.org> To: Hannes Reinecke <hare@...e.de> Cc: Chris Leech <cleech@...hat.com>, 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 Sun, Oct 01, 2023 at 12:44:05PM +0200, Hannes Reinecke wrote: > On 9/30/23 20:28, Greg Kroah-Hartman wrote: > > On Sat, Sep 30, 2023 at 11:19:20AM -0700, Chris Leech wrote: > > > 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. > > > > That's horrible, and not what the UIO api is for at all. Configure the > > device like any other normal kernel device, don't poke at raw memory > > values directly, that way lies madness. > > > > Have a pointer to the userspace tool anywhere? All I found looks like a > > full IP stack in userspace under that name, and surely that's not what > > this api is for... > > > But that's how the interface is used, in particular for the bnx2i driver. > Problem is that the bnx2i iSCSI offload is just that, an iSCSI offload. Not > a TCP offload. So if the iSCSI interface is configured to > acquire the IP address via DHCP, someone has to run the DHCP protocol. > But the iSCSI offload can't, and the bnx2i PCI device is not a network > device so that the normal network stack can't be used. > And so the architects of the bnx2i card decided to use UIO to pass > the network traffic to userspace, and used the userspace 'iscsiuio' > application to run DHCP in userspace. > > But's been that way for several years now; so long, in fact, that > the card itself has been out of support from Marvell (since quite some > years, too, IIRC). And even the successor of that card (the qedi driver) > is nearing EOL. Mind you, the qedi driver is using the same interface (by > using UIO to run DHCP in userspace), so singling out the bnx2i for bad > design can be construed as being unfair :-) Ok, let's say they are all horrible! :) > I agree, though, that the design is a mess. Ok, so why are we papering over it and continuing to allow it to exist? What "broke" to suddenly require this UIO change? If this has been around for a very long time, what has caused this to now require the UIO layer to change? thanks, greg k-h
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