linux-kernel - Re: IB on s390 broken with commit 99db94940 "IB/core: Remove ib_device.dma

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Date:   Tue, 28 Feb 2017 10:20:00 +0100 (CET)
From:   Sebastian Ott <sebott@...ux.vnet.ibm.com>
To:     Bart Van Assche <Bart.VanAssche@...disk.com>
cc:     "dledford@...hat.com" <dledford@...hat.com>,
        "gerald.schaefer@...ibm.com" <gerald.schaefer@...ibm.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: Re: IB on s390 broken with commit 99db94940 "IB/core: Remove
 ib_device.dma_device"

On Tue, 28 Feb 2017, Sebastian Ott wrote:
> On Mon, 27 Feb 2017, Bart Van Assche wrote:
> > On Mon, 2017-02-27 at 21:17 +0100, Sebastian Ott wrote:
> > > commit 99db94940 "IB/core: Remove ib_device.dma_device"
> > > breaks infiniband on s390 (and I think also other archs that do something
> > > like to_pci_dev(dev) in one of their dma_ops callbacks).
> > > 
> > > With this commit you use the dma_ops of the device that called
> > > ib_register_device but you call e.g. dma_map with ib_device->dev
> > > as an argument.
> > > 
> > > S390's (pci specific) dma_map uses to_pci_dev(dev) to look into the
> > > pci device (and its arch specific data) and oopses.
> > > 
> > > Calling dma_map with ib_device->dev.parent would work but then it
> > > wouldn't make sense to copy dma_ops and mask from ib_device->dev.parent
> > > to ib_device->dev..
> > 
> > How about something like the untested patch below?
> 
> It works but it doesn't feel right (why should all pci devices have this
> duplicated data).
> 
> Frankly I don't get the usecase of infiniband (sometimes) using
> device->dev.dma_ops instead of parent->dma_ops.

Ok, some drivers in drivers/infiniband/sw/ set dma_ops to &dma_virt_ops .

So instead of copying the dma_ops you could do

if (!device->dev.dma_ops) /*or use some new flag for ib_register_device*/
	device->dma_device = parent;
else
	device->dma_device = &device->dev;

Sebastian