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Date:   Wed, 26 May 2021 16:53:21 +0100
From:   Will Deacon <will@...nel.org>
To:     Claire Chang <tientzu@...omium.org>
Cc:     Rob Herring <robh+dt@...nel.org>, mpe@...erman.id.au,
        Joerg Roedel <joro@...tes.org>,
        Frank Rowand <frowand.list@...il.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        benh@...nel.crashing.org, paulus@...ba.org,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        sstabellini@...nel.org, Robin Murphy <robin.murphy@....com>,
        grant.likely@....com, xypron.glpk@....de,
        Thierry Reding <treding@...dia.com>, mingo@...nel.org,
        bauerman@...ux.ibm.com, peterz@...radead.org,
        Greg KH <gregkh@...uxfoundation.org>,
        Saravana Kannan <saravanak@...gle.com>,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        heikki.krogerus@...ux.intel.com,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        linux-devicetree <devicetree@...r.kernel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        linuxppc-dev@...ts.ozlabs.org, xen-devel@...ts.xenproject.org,
        Nicolas Boichat <drinkcat@...omium.org>,
        Jim Quinlan <james.quinlan@...adcom.com>, tfiga@...omium.org,
        bskeggs@...hat.com, bhelgaas@...gle.com, chris@...is-wilson.co.uk,
        daniel@...ll.ch, airlied@...ux.ie, dri-devel@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org, jani.nikula@...ux.intel.com,
        jxgao@...gle.com, joonas.lahtinen@...ux.intel.com,
        linux-pci@...r.kernel.org, maarten.lankhorst@...ux.intel.com,
        matthew.auld@...el.com, rodrigo.vivi@...el.com,
        thomas.hellstrom@...ux.intel.com
Subject: Re: [PATCH v7 14/15] dt-bindings: of: Add restricted DMA pool

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@...00000, 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;
 }

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