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@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)
>
>
> #if CONFIG_IS_ENABLED(DM)
> #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.
Regards,
Nicolas
[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/arch/arm/boot/dts/bcm2711.dtsi?h=v5.12-rc3#n506
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