[RFC] dev_phys_to_bus() and PCI

Nicolas Saenz Julienne nsaenzjulienne at suse.de
Mon Mar 15 11:26:18 CET 2021

Hi Mark!

On Sat, 2021-03-13 at 10:24 +0100, Mark Kettenis wrote:
> Fortunately Nicolas Saenz Julienne recently introduced
> dev_phys_to_bus() and dev_bus_to_phys() interfaces to do this.  Those
> interfaces make use of a dma-ranges property in the device tree which
> doesn't work so well for PCI devices though.

Why doesn't it work with PCI devices? Raspberry Pi 4 has a PCIe bus that needs
DMA translations. This is handled by parsing its 'dma-ranges' property. Here's
how rpi4's devicetree looks like[1]:

	pcie0: pcie at 7d500000 {
		compatible = "brcm,bcm2711-pcie";
		ranges = <0x02000000 0x0 0xf8000000 0x6 0x00000000 0x0 0x04000000>;
		 * The wrapper around the PCIe block has a bug preventing it
		 * from accessing beyond the first 3GB of memory.
		dma-ranges = <0x02000000 0x0 0x00000000 0x0 0x00000000 0x0 0xc0000000>;

> However, the PCI code in U-Boot already has a way to describe DMA address
> translation through its regions support.

regions contain a representation of devicetree's 'ranges' property, which
doesn't describe the DMA address translations, but CPU's view of PCI memory.

> diff --git a/include/phys2bus.h b/include/phys2bus.h
> index 866b8b51a8..13d23ef4bb 100644
> --- a/include/phys2bus.h
> +++ b/include/phys2bus.h
> @@ -23,14 +23,21 @@ static inline unsigned long bus_to_phys(unsigned long bus)
>  #include <dm/device.h>
> +#include <pci.h>
>  static inline dma_addr_t dev_phys_to_bus(struct udevice *dev, phys_addr_t phys)
>  {
> +	if (device_is_on_pci_bus(dev))
> +		return dm_pci_phys_to_bus(dev, phys, PCI_REGION_SYS_MEMORY);
> +

Note that this would break USB support on RPi4.



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