linux-kernel - Re: [PATCH v2 3/5] iommu: Add verisilicon IOMMU driver

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Message-ID: <20250618145723.GR1376515@ziepe.ca>
Date: Wed, 18 Jun 2025 11:57:23 -0300
From: Jason Gunthorpe <jgg@...pe.ca>
To: Benjamin Gaignard <benjamin.gaignard@...labora.com>
Cc: joro@...tes.org, will@...nel.org, robin.murphy@....com, robh@...nel.org,
	krzk+dt@...nel.org, conor+dt@...nel.org, heiko@...ech.de,
	nicolas.dufresne@...labora.com, iommu@...ts.linux.dev,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, kernel@...labora.com
Subject: Re: [PATCH v2 3/5] iommu: Add verisilicon IOMMU driver

On Wed, Jun 18, 2025 at 04:09:12PM +0200, Benjamin Gaignard wrote:
> +config VSI_IOMMU
> +	bool "Verisilicon IOMMU Support"
> +	depends on ARM64
> +	select IOMMU_API
> +	select ARM_DMA_USE_IOMMU

ARM_DMA_USE_IOMMU is only used by ARM32, you don't need it if you
depends on ARM64

> +static void vsi_iommu_release_device(struct device *dev)
> +{
> +	struct vsi_iommu *iommu = dev_iommu_priv_get(dev);
> +
> +	device_link_remove(dev, iommu->dev);
> +}

This does not seem right, release is supposed to reprogram the HW to
stop walking any page table.

You should implement a static blocked (or identity?) domain that idles
the hardware and use that as the blocked and release_domain in the
ops.

The logic around vsi_iommu_detach_device() and
vsi_iommu_attach_device() is also not quite right. The attach can
happen while iommu->domain is already set and doesn't deal with
removing the iommu from the old domain's list.

I would probably change vsi_iommu_enable() into vsi_iommu_set_paging()
and then presumably vsi_iommu_disable() is vsi_iommu_set_blocking() ?

vsi_iommu_detach_device() should be deleted and integrated into the
blocked domain and attach error unwind.

> +static int vsi_iommu_of_xlate(struct device *dev,
> +			      const struct of_phandle_args *args)
> +{
> +	struct platform_device *iommu_dev;
> +
> +	if (!dev_iommu_priv_get(dev)) {
> +		iommu_dev = of_find_device_by_node(args->np);
> +		if (WARN_ON(!iommu_dev))
> +			return -EINVAL;
> +
> +		dev_iommu_priv_set(dev, platform_get_drvdata(iommu_dev));
> +	}

The driver should ideally not be calling dev_iommu_priv_set/get here,
and this leads the reference doesn't it? Do what ARM did to locate
the iommu_dev.

I would also add a comment here:

> +static int vsi_iommu_map(struct iommu_domain *domain, unsigned long _iova,
> +                        phys_addr_t paddr, size_t size, size_t count,
> +                        int prot, gfp_t gfp, size_t *mapped)
> +{
> +       struct vsi_iommu_domain *vsi_domain = to_vsi_domain(domain);
> +       unsigned long flags;
> +       dma_addr_t pte_dma, iova = (dma_addr_t)_iova;
> +       u32 *page_table, *pte_addr;
> +       u32 dte, pte_index;
> +       int ret;

/*
 * IOMMU drivers are not supposed to lock the page table, however this
 * driver does not safely handle the cache flushing or table
 * installation across concurrent threads so locking is used as a simple
 * solution.
 */

> +       spin_lock_irqsave(&vsi_domain->dt_lock, flags);

Jason