Re: [PATCH 02/11] driver core: Set DMA ownership during driver bind/unbind

Christoph Hellwig
2021-11-16T00:53:57Z

On Mon, Nov 15, 2021 at 11:56:13AM -0400, Jason Gunthorpe wrote:
> drivers/base/platform.c: .dma_configure = platform_dma_configure,
> drivers/bus/fsl-mc/fsl-mc-bus.c: .dma_configure = fsl_mc_dma_configure,
> drivers/pci/pci-driver.c: .dma_configure = pci_dma_configure,
> drivers/gpu/host1x/bus.c: .dma_configure = host1x_dma_configure,
>
> Other than host1x they all work with VFIO.
>
> Also, there is no bus->dma_unconfigure() which would be needed to
> restore the device as well.
>
> So, would you rather see duplicated code into the 4 drivers, and a new
> bus op to 'unconfigure dma'

The tend to mostly call into common helpers eventually.

>
> Or, a 'dev_configure_dma()' function that is roughly:
>
> if (dev->bus->dma_configure) {
> ret = dev->bus->dma_configure(dev);
> if (ret)
> return ret;
> if (!drv->suppress_auto_claim_dma_owner) {
> ret = iommu_device_set_dma_owner(dev, DMA_OWNER_KERNEL,
> NULL);
> if (ret)
> ret;
> }
> }
>
> And a pair'd undo.

But that seems like an even better idea to me. Even better with an
early return and avoiding the pointless indentation.