On Tue, Aug 15, 2023 at 9:51 PM James Liu <james.liu@xxxxxxx> wrote: > > On Mon, Jun 12, 2023 at 06:57:01PM +0200, Rafael J. Wysocki wrote: > > On Thu, Jun 8, 2023 at 11:14 AM James Liu <james.liu@xxxxxxx> wrote: > > > > > > On Wed, Jun 07, 2023 at 01:19:42PM +0200, Rafael J. Wysocki wrote: > > > > On Wed, Jun 7, 2023 at 5:44 AM James Liu <james.liu@xxxxxxx> wrote: > > > > > > > > > > For AMD Milan platforms, the delay of 15ms is insufficient to avoid racing > > > > > of reboot mechanisms. That said, the AMD Milan processors don't reboot > > > > > in 15ms after invoking acpi_reset(). > > > > > > > > > > The proposed 50ms delay can effectively work around this issue. > > > > > This extended delay aligns better with ACPI v6.4 (i.e., sec. 4.8.4.6), > > > > > which indicates that ideally OSPM should execute spin loops on the CPUs > > > > > in the system following a write to this register. > > > > > > > > > > Signed-off-by: James Liu <james.liu@xxxxxxx> > > > > > > > > Why do you want to affect everyone (including guest kernels running in > > > > virtual machines AFAICS) in order to address a problem specific to one > > > > platform? > > > > > > I hoped to address this issue for any platform requiring a longer delay to > > > complete ACPI reset in time for any (maybe silicon-level) reasons. Some AMD Milan > > > platforms were the cases that we've found so far. > > > > Do you know about any other? > > So far, no. Thus, I wont' proceed with anything until I find the same syndrome > on next-gen platforms (e.g., AMD Genoa). Now, as you say, it is satisfying to > document this quirk properly. > > > > > > Except that, since ACPI spec indicates there should be a spin loop (long enough) > > > after the write instruction to Reset Register, I thought it should be no harms to > > > the other systems which well consider this spin loop when they claim to support > > > ACPI reboot. > > > > > > Btw, I am just curious, why is the virtual machine mentioned here? > > > > The new delay would be over 3 times larger, so some users might be > > surprised by it at least potentially. > > Got it. Just in case, if we really need to increase the delay to address it for > certain amount of platforms, in experience, how long is the delay acceptable so > that VM users will not be surprised? Honestly, I don't know. Also, it is not quite clear to me from the changelog what the problem with the Milan platforms vs the reboot delay is and I don't think that the second paragraph (regarding the ACPI specification compliance) is relevant for this patch at all.
