XHCI bringup on the Raspberry Pi 4

[Marek Vasut]

On 4/1/20 7:30 PM, Nicolas Saenz Julienne wrote:
> Hi All,

Hi,

> I'm working on enabling the VIA805 XCHI controller found on the new Raspberry
> Pi 4. The controller sits behind a PCIe bus, which I've already implemented[1]
> and will submit once the XCHI issues are resolved, as it's worthless otherwise.
> 
> The XHCI initialization gets stuck after issuing the fist 'enable slot'
> command. I've been reviewing the whole init process and comparing it to Linux's
> for days without finding anything fishy. DMA constraints, which are important
> on the RPi are mantained, and on top of that, I can confirm DMA trough PCIe
> works fine as I see two 'port status change' events available in the ring
> before completly stalling. Also note that, unsurprisingly, the CRR bit in the
> CRCR register (which marks the running state of the Command Ring state machine)
> is never set after ringing the relevant doorbell.
> 
> I'm clueless at this point, I figure the VIA805 is sensitive to the ordering of
> some of the operations we perform in u-boot, or worse, the timing. For example,
> I tried replicanting Linux's behaviour with regard to 'port status change'
> events, processing them before calling the 'enable slot' command. I also tried
> to mimic Linux by enabling port-0's power (the USB3 port) before starting the
> HC. Again, no luck.
> 
> I attached the usb/xhci debug output, any ideas on where to look will be
> apreciated.

Try disabling caches (dcache off ; icache off) and see if it magically
starts working. That comes to mind.