Re: [PATCH v5 16/16] of: Add plumbing for restricted DMA pool

On Fri, Apr 23, 2021 at 9:35 PM Robin Murphy robin.murphy@arm.com wrote:

On 2021-04-22 09:15, Claire Chang wrote:

...

If a device is not behind an IOMMU, we look up the device node and set up the restricted DMA when the restricted-dma-pool is presented.

Signed-off-by: Claire Chang tientzu@chromium.org

drivers/of/address.c | 25 +++++++++++++++++++++++++ drivers/of/device.c | 3 +++ drivers/of/of_private.h | 5 +++++ 3 files changed, 33 insertions(+)

diff --git a/drivers/of/address.c b/drivers/of/address.c index 54f221dde267..fff3adfe4986 100644 --- a/drivers/of/address.c +++ b/drivers/of/address.c @@ -8,6 +8,7 @@ #include <linux/logic_pio.h> #include <linux/module.h> #include <linux/of_address.h> +#include <linux/of_reserved_mem.h> #include <linux/pci.h> #include <linux/pci_regs.h> #include <linux/sizes.h> @@ -1109,6 +1110,30 @@ 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) +{

• struct device_node *node;
  

• int count, i;
  

• if (!dev->of_node)
  

•         return 0;
  

• count = of_property_count_elems_of_size(dev->of_node, "memory-region",
  

•                                         sizeof(phandle));
  

• for (i = 0; i < count; i++) {
  

•         node = of_parse_phandle(dev->of_node, "memory-region", i);
  

•         /* There might be multiple memory regions, but only one
  

•          * restriced-dma-pool region is allowed.
  

•          */
  

What's the use-case for having multiple regions if the restricted pool is by definition the only one accessible?

There might be a device coherent pool (shared-dma-pool) and dma_alloc_attrs might allocate memory from that pool [1]. I'm not sure if it makes sense to have another device coherent pool while using restricted DMA pool though.

[1] https://elixir.bootlin.com/linux/v5.12/source/kernel/dma/mapping.c#L435

Robin.

...

•         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 0;
  

+}

• /**
  • of_mmio_is_nonposted - Check if device uses non-posted MMIO
  • @np: device node

diff --git a/drivers/of/device.c b/drivers/of/device.c index c5a9473a5fb1..d8d865223e51 100644 --- a/drivers/of/device.c +++ b/drivers/of/device.c @@ -165,6 +165,9 @@ 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 0;
  

  } EXPORT_SYMBOL_GPL(of_dma_configure_id);

diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h index d717efbd637d..e9237f5eff48 100644 --- a/drivers/of/of_private.h +++ b/drivers/of/of_private.h @@ -163,12 +163,17 @@ 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); #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_get_restricted_buffer(struct device *dev) +{

• return -ENODEV;
  

+} #endif

#endif /* _LINUX_OF_PRIVATE_H */