Re: [PATCH v7 14/15] dt-bindings: of: Add restricted DMA pool

[Will Deacon <will@kernel.org>]

On Wed, May 26, 2021 at 01:13:22PM +0100, Will Deacon wrote:
> On Tue, May 18, 2021 at 02:42:14PM +0800, Claire Chang wrote:
> > @@ -138,4 +160,9 @@ one for multimedia processing (named multimedia-memory@77000000, 64MiB).
> >  		memory-region = <&multimedia_reserved>;
> >  		/* ... */
> >  	};
> > +
> > +	pcie_device: pcie_device@0,0 {
> > +		memory-region = <&restricted_dma_mem_reserved>;
> > +		/* ... */
> > +	};
> 
> I still don't understand how this works for individual PCIe devices -- how
> is dev->of_node set to point at the node you have above?
> 
> I tried adding the memory-region to the host controller instead, and then
> I see it crop up in dmesg:
> 
>   | pci-host-generic 40000000.pci: assigned reserved memory node restricted_dma_mem_reserved
> 
> but none of the actual PCI devices end up with 'dma_io_tlb_mem' set, and
> so the restricted DMA area is not used. In fact, swiotlb isn't used at all.
> 
> What am I missing to make this work with PCIe devices?

Aha, looks like we're just missing the logic to inherit the DMA
configuration. The diff below gets things working for me.

Will

--->8

diff --git a/drivers/of/address.c b/drivers/of/address.c
index c562a9ff5f0b..bf499fdd6e93 100644
--- a/drivers/of/address.c
+++ b/drivers/of/address.c
@@ -1113,25 +1113,25 @@ bool of_dma_is_coherent(struct device_node *np)
 }
 EXPORT_SYMBOL_GPL(of_dma_is_coherent);
 
-int of_dma_set_restricted_buffer(struct device *dev)
+int of_dma_set_restricted_buffer(struct device *dev, struct device_node *np)
 {
-	struct device_node *node;
 	int count, i;
 
-	if (!dev->of_node)
+	if (!np)
 		return 0;
 
-	count = of_property_count_elems_of_size(dev->of_node, "memory-region",
+	count = of_property_count_elems_of_size(np, "memory-region",
 						sizeof(phandle));
 	for (i = 0; i < count; i++) {
-		node = of_parse_phandle(dev->of_node, "memory-region", i);
+		struct device_node *node;
+
+		node = of_parse_phandle(np, "memory-region", i);
 		/* There might be multiple memory regions, but only one
-		 * restriced-dma-pool region is allowed.
+		 * restricted-dma-pool region is allowed.
 		 */
 		if (of_device_is_compatible(node, "restricted-dma-pool") &&
 		    of_device_is_available(node))
-			return of_reserved_mem_device_init_by_idx(
-				dev, dev->of_node, i);
+			return of_reserved_mem_device_init_by_idx(dev, np, i);
 	}
 
 	return 0;
diff --git a/drivers/of/device.c b/drivers/of/device.c
index d8d865223e51..2defdca418ec 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -166,7 +166,7 @@ int of_dma_configure_id(struct device *dev, struct device_node *np,
 	arch_setup_dma_ops(dev, dma_start, size, iommu, coherent);
 
 	if (!iommu)
-		return of_dma_set_restricted_buffer(dev);
+		return of_dma_set_restricted_buffer(dev, np);
 
 	return 0;
 }
diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index 9fc874548528..8fde97565d11 100644
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h
@@ -163,14 +163,15 @@ struct bus_dma_region;
 #if defined(CONFIG_OF_ADDRESS) && defined(CONFIG_HAS_DMA)
 int of_dma_get_range(struct device_node *np,
 		const struct bus_dma_region **map);
-int of_dma_set_restricted_buffer(struct device *dev);
+int of_dma_set_restricted_buffer(struct device *dev, struct device_node *np);
 #else
 static inline int of_dma_get_range(struct device_node *np,
 		const struct bus_dma_region **map)
 {
 	return -ENODEV;
 }
-static inline int of_dma_set_restricted_buffer(struct device *dev)
+static inline int of_dma_set_restricted_buffer(struct device *dev,
+					       struct device_node *np)
 {
 	return -ENODEV;
 }