Re: [PATCH v2] usb: host: xhci-plat: Assign shared_hcd->rsrc_start

[Mathias Nyman <mathias.nyman@linux.intel.com>]

On 4.1.2025 17.51, WangYuli wrote:
> When inserting a USB device, examining hcd->rsrc_start can be
> helpful in identifying which hcd is mounted, as the physical
> address represented here is typically unique.
> 
> The following code snippet demonstrates this:
>    struct usb_hcd *hcd = bus_to_hcd(udev->bus);
>    unsigned long long usb_hcd_addr = (unsigned long long)hcd->rsrc_start;
> 
> However, this approach has limitations now. For USB hosts with an
> MMIO interface, the effectiveness of this method is restricted to
> USB 2.0.
> 
> Becase commit 3429e91a661e ("usb: host: xhci: add platform driver
> support") assigned res->start to hcd->rsrc_start. But
> shared_hcd->rsrc_start remains unassigned, which is also necessary
> in certain scenarios.

Could you expand on those scenarios?

Is it possible those could be solved with something like:

unsigned long long usb_hcd_addr;
struct usb_hcd *hcd = bus_to_hcd(udev->bus);

if (!usb_hcd_is_primary_hcd(hcd))
	hcd = hcd->primary_hcd;
usb_hcd_addr = (unsigned long long)hcd->rsrc_start;

That should work for all hcds.

Thanks
Mathias