On Tue, 2017-08-01 at 01:48 +0200, Jaroslav Jindrák wrote: > Hello, > > I'd like to submit a patch to the xhci subsystem of QEMU. Currently, > when the command stop or command abort flags in the crcr_low register > are set, nothing happens. This is because the part of the code that > tests those two flags (and performs command ring abort/stop) is in > the crcr_high case. This error has a simple workaround - after > writing to the crcr_low register with either of these two flags set, > one can write the value of crcr_high to crcr_high, so I > assume this fix does not have that big of a priority, but a driver > that follows the specification strictly would misbehave in this kind > of situation (stopping/aborting the command ring).
Specs says (section 5.1, Register Conventions): <quote> If the xHC supports 64-bit addressing (AC64 = ‘1’), then software should write registers containing 64-bit address fields using only Qword accesses. If a system is incapable of issuing Qword accesses, then writes to the 64-bit address fields shall be performed using 2 Dword accesses; low Dword-first, high-Dword second. </quote> So I think the guest must write both crcr_low and crcr_high, and the qemu behavior is correct. Are there any guests which actually have problems? cheers, Gerd
