Re: [PATCH v5 2/5] iommu: Implement of_iommu_get_resv_regions()

[Thierry Reding <thierry.reding@gmail.com>]

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On Sun, May 15, 2022 at 01:10:38PM +0200, Janne Grunau wrote:
> On 2022-05-12 21:00:49 +0200, Thierry Reding wrote:
> > From: Thierry Reding <treding@nvidia.com>
> > 
> > This is an implementation that IOMMU drivers can use to obtain reserved
> > memory regions from a device tree node. It uses the reserved-memory DT
> > bindings to find the regions associated with a given device. If these
> > regions are marked accordingly, identity mappings will be created for
> > them in the IOMMU domain that the devices will be attached to.
> > 
> > Signed-off-by: Thierry Reding <treding@nvidia.com>
> > ---
> > Changes in v5:
> > - update for new "iommu-addresses" device tree bindings
> > 
> > Changes in v4:
> > - fix build failure on !CONFIG_OF_ADDRESS
> > 
> > Changes in v3:
> > - change "active" property to identity mapping flag that is part of the
> >   memory region specifier (as defined by #memory-region-cells) to allow
> >   per-reference flags to be used
> > 
> > Changes in v2:
> > - use "active" property to determine whether direct mappings are needed
> > 
> >  drivers/iommu/of_iommu.c | 90 ++++++++++++++++++++++++++++++++++++++++
> >  include/linux/of_iommu.h |  8 ++++
> >  2 files changed, 98 insertions(+)
> > 
> > diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> > index 5696314ae69e..9e341b5e307f 100644
> > --- a/drivers/iommu/of_iommu.c
> > +++ b/drivers/iommu/of_iommu.c
> > @@ -11,12 +11,15 @@
> >  #include <linux/module.h>
> >  #include <linux/msi.h>
> >  #include <linux/of.h>
> > +#include <linux/of_address.h>
> >  #include <linux/of_iommu.h>
> >  #include <linux/of_pci.h>
> >  #include <linux/pci.h>
> >  #include <linux/slab.h>
> >  #include <linux/fsl/mc.h>
> >  
> > +#include <dt-bindings/reserved-memory.h>
> > +
> >  #define NO_IOMMU	1
> >  
> >  static int of_iommu_xlate(struct device *dev,
> > @@ -172,3 +175,90 @@ const struct iommu_ops *of_iommu_configure(struct device *dev,
> >  
> >  	return ops;
> >  }
> > +
> > +/**
> > + * of_iommu_get_resv_regions - reserved region driver helper for device tree
> > + * @dev: device for which to get reserved regions
> > + * @list: reserved region list
> > + *
> > + * IOMMU drivers can use this to implement their .get_resv_regions() callback
> > + * for memory regions attached to a device tree node. See the reserved-memory
> > + * device tree bindings on how to use these:
> > + *
> > + *   Documentation/devicetree/bindings/reserved-memory/reserved-memory.txt
> > + */
> > +void of_iommu_get_resv_regions(struct device *dev, struct list_head *list)
> > +{
> > +#if IS_ENABLED(CONFIG_OF_ADDRESS)
> > +	struct of_phandle_iterator it;
> > +	int err;
> > +
> > +	of_for_each_phandle(&it, err, dev->of_node, "memory-region", NULL, 0) {
> > +		struct iommu_resv_region *region;
> > +		struct resource res;
> > +		const __be32 *maps;
> > +		int size;
> 
> Adding 'if (!of_device_is_available(it.node)) continue;' here would help 
> backwards compatibility. My plan was to add the reserved regions with 
> "iommu-addresses" with all zero adresses and sizes with status = 
> "disabled" to the devicetree. A bootloader update is required to fill 
> those.

Yes, good point. My plan was originally to have the bootloader/firmware
generate these nodes in their entirety, but yeah, prepopulating them and
having firmware just fill in updated values and setting status = "okay"
seems reasonable to me.

> > +
> > +		memset(&res, 0, sizeof(res));
> > +
> > +		/*
> > +		 * The "reg" property is optional and can be omitted by reserved-memory regions
> > +		 * that represent reservations in the IOVA space, which are regions that should
> > +		 * not be mapped.
> > +		 */
> > +		if (of_find_property(it.node, "reg", NULL)) {
> > +			err = of_address_to_resource(it.node, 0, &res);
> > +			if (err < 0) {
> > +				dev_err(dev, "failed to parse memory region %pOF: %d\n",
> > +					it.node, err);
> > +				continue;
> > +			}
> > +		}
> > +
> > +		maps = of_get_property(it.node, "iommu-addresses", &size);
> > +		if (maps) {
> > +			const __be32 *end = maps + size / sizeof(__be32);
> > +			struct device_node *np;
> > +			unsigned int index = 0;
> > +			u32 phandle;
> > +			int na, ns;
> > +
> > +			while (maps < end) {
> > +				phys_addr_t start, end;
> > +				size_t length;
> > +
> > +				phandle = be32_to_cpup(maps++);
> > +				np = of_find_node_by_phandle(phandle);
> > +				na = of_n_addr_cells(np);
> > +				ns = of_n_size_cells(np);
> > +
> > +				start = of_translate_dma_address(np, maps);
> > +				length = of_read_number(maps + na, ns);
> 
> alternatively we could handle mappings/reservations with length 0 as 
> error and skip them.

I think we could do both.

Thanks for the feedback,
Thierry

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