Hi Sylwester,
On Mon, 25 May 2020 at 10:57, Sylwester Nawrocki s.nawrocki@samsung.com wrote:
Hi Simon,
On 25.05.2020 16:57, Simon Glass wrote:
On Mon, 25 May 2020 at 05:40, Sylwester Nawrocki s.nawrocki@samsung.com wrote:
There might be hardware configurations where 64-bit data accesses to XHCI registers are not supported properly. This patch removes the readq/writeq so always two 32-bit accesses are used to read/write 64-bit XHCI registers, similarly as it is done in Linux kernel.
This patch fixes operation of the XHCI controller on RPI4 Broadcom BCM2711 SoC based board, where the VL805 USB XHCI controller is connected to the PCIe Root Complex, which is attached to the system through the SCB bridge.
Even though the architecture is 64-bit the PCIe BAR is 32-bit and likely the 64-bit wide register accesses initiated by the CPU are not properly translated to a sequence of 32-bit PCIe accesses. xhci_readq(), for example, always returns same value in upper and lower 32-bits, e.g. 0xabcd1234abcd1234 instead of 0x00000000abcd1234.
Then I think this should be done with a quirk flag, enabled for this particular device via the compatible string. It should not be an #if, but an if().
Thanks for your comments. I will check and see how this could be done. It might not be so straightforward since the XHCI controller is a PCI device matched by the pci_device_id so we would need to be looking at the compatible string of the PCI controller to set the quirk in the xhci layer. It's the PCI bridge that introduces the limitation, not the VL805 XHCI controller chip.
OK then it should be modelled as such.
How is this done in Linux?
You can add a quirk in the PCI controller and then XHCI can check its parent's platdata to see the flag, perhaps, since the parent will always be UCLASS_PCI.
You can always add the device to the devicetree if needed, and then you get a compatible string.
Regards, Simon