Re: [edk2-devel] [PATCH] MdeModulePkg/XhciDxe: Use Performance Timer for XHCI Timeouts

["Michael Brown" <mcb30@ipxe.org>]

On 05/07/2023 21:15, Henz, Patrick wrote:
> REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2948
> 
> XhciDxe uses the timer functionality provided by the
> boot services table to detect timeout conditions. This
> breaks the driver's ExitBootServices call back, as
> CoreExitBootServices halts the timer before signaling
> the ExitBootServices event. If the host controller
> fails to halt in the call back, the timeout condition
> will never occur and the boot gets stuck in an indefinite
> spin loop. Use the free running timer provided by
> TimerLib to calculate timeouts, avoiding the potential
> hang.

Two points:

1. The XhcGetElapsedTime() function feels like a generally reusable 
abstraction that should exist within TimerLib, rather than being 
open-coded within XhciDxe.

2. Is the performance counter guaranteed to exist and work as expected 
on all platforms and CPU architectures?  (For example: what if the CPU 
does not support a constant TSC?)

Thanks,

Michael