linux-kernel - Re: [PATCH v6 4/6] s390/pci: Use dma-iommu layer

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Date:   Wed, 15 Feb 2023 13:00:08 -0500
From:   Matthew Rosato <mjrosato@...ux.ibm.com>
To:     Niklas Schnelle <schnelle@...ux.ibm.com>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Wenjia Zhang <wenjia@...ux.ibm.com>
Cc:     Gerd Bayer <gbayer@...ux.ibm.com>,
        Pierre Morel <pmorel@...ux.ibm.com>, iommu@...ts.linux.dev,
        linux-s390@...r.kernel.org, borntraeger@...ux.ibm.com,
        hca@...ux.ibm.com, gor@...ux.ibm.com,
        gerald.schaefer@...ux.ibm.com, agordeev@...ux.ibm.com,
        svens@...ux.ibm.com, linux-kernel@...r.kernel.org,
        Julian Ruess <julianr@...ux.ibm.com>
Subject: Re: [PATCH v6 4/6] s390/pci: Use dma-iommu layer

On 2/15/23 7:03 AM, Niklas Schnelle wrote:
> While s390 already has a standard IOMMU driver and previous changes have
> added I/O TLB flushing operations this driver is currently only used for
> user-space PCI access such as vfio-pci. For the DMA API s390 instead
> utilizes its own implementation in arch/s390/pci/pci_dma.c which drives
> the same hardware and shares some code but requires a complex and
> fragile hand over between DMA API and IOMMU API use of a device and
> despite code sharing still leads to significant duplication and
> maintenance effort. Let's utilize the common code DMAP API
> implementation from drivers/iommu/dma-iommu.c instead allowing us to
> get rid of arch/s390/pci/pci_dma.c.
> 
> Signed-off-by: Niklas Schnelle <schnelle@...ux.ibm.com>
> ---

FYI, this patch doesn't fit on top of iommu-next, I'd guess at least due to baolu's 'Retire detach_dev callback' series, which removed .detach_dev and added .set_platform_dma_ops for s390-iommu.  That's relevant here, because now that this patch enables dma-iommu for s390 and removes the platform DMA ops it must now remove .set_platform_dma_ops/s390_iommu_set_platform_dma for s390-iommu.

Matt