linux-kernel - Re: [PATCH v5 07/14] PCI: Add driver dma ownership management

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Date:   Wed, 23 Feb 2022 12:00:56 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Jason Gunthorpe <jgg@...dia.com>,
        Christoph Hellwig <hch@...radead.org>,
        Kevin Tian <kevin.tian@...el.com>,
        Ashok Raj <ashok.raj@...el.com>, kvm@...r.kernel.org,
        rafael@...nel.org, David Airlie <airlied@...ux.ie>,
        linux-pci@...r.kernel.org,
        Thierry Reding <thierry.reding@...il.com>,
        Diana Craciun <diana.craciun@....nxp.com>,
        Dmitry Osipenko <digetx@...il.com>,
        Will Deacon <will@...nel.org>,
        Stuart Yoder <stuyoder@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Cornelia Huck <cohuck@...hat.com>,
        linux-kernel@...r.kernel.org, Li Yang <leoyang.li@....com>,
        iommu@...ts.linux-foundation.org,
        Jacob jun Pan <jacob.jun.pan@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH v5 07/14] PCI: Add driver dma ownership management

In subject,

s/dma/DMA/ to match the other patches

On Tue, Jan 04, 2022 at 09:56:37AM +0800, Lu Baolu wrote:
> Multiple PCI devices may be placed in the same IOMMU group because
> they cannot be isolated from each other. These devices must either be
> entirely under kernel control or userspace control, never a mixture. This
> checks and sets DMA ownership during driver binding, and release the
> ownership during driver unbinding.
> 
> The device driver may set a new flag (no_kernel_api_dma) to skip calling
> iommu_device_use_dma_api() during the binding process. For instance, the
> userspace framework drivers (vfio etc.) which need to manually claim
> their own dma ownership when assigning the device to userspace.

s/vfio/VFIO/ when used as an acronym (occurs in several patches)

> + * @no_kernel_api_dma: Device driver doesn't use kernel DMA API for DMA.
> + *		Drivers which don't require DMA or want to manually claim the
> + *		owner type (e.g. userspace driver frameworks) could set this
> + *		flag.

s/Drivers which/Drivers that/

>  static int pci_dma_configure(struct device *dev)
>  {
> +	struct pci_driver *driver = to_pci_driver(dev->driver);
>  	struct device *bridge;
>  	int ret = 0;
>  
> +	if (!driver->no_kernel_api_dma) {

Ugh.  Double negative, totally agree this needs a better name that
reverses the sense.  Every place you use it, you negate it again.

> +	if (ret && !driver->no_kernel_api_dma)
> +		iommu_device_unuse_dma_api(dev);

> +static void pci_dma_cleanup(struct device *dev)
> +{
> +	struct pci_driver *driver = to_pci_driver(dev->driver);
> +
> +	if (!driver->no_kernel_api_dma)
> +		iommu_device_unuse_dma_api(dev);