Daniel Axtens <d...@axtens.net> writes: > I just realised I sent my reply to Denis not the list - apologies. This > info goes for v2 as well. > > > Could you explain why it's useful, and what it's useful for. Moreover, > > it's POWER8 feature, right? > > I'm not sure whether you're asking about the script or HMIs. Explaining > HMIs helps make sense of the script, so I'll start there. > > HMIs are a class of interrupt or exception that, broadly speaking, > require the hypervisor to intervene to 'do something'. They are (very > lightly) documented in the POWER ISA, which is available on the > OpenPOWER website. That file doesn't do a particuarly good job of > explaining what can trigger an HMI, because that's a Book IV question. > > So, while I can't point you to documentation about what might cause an > HMI, I can point you to some source code. Here goes: > > An HMI will (per the ISA) cause execution to jump to > 0x0000 0000 0000 0E60. Through some asm and C you end up calling > ppc_md.hmi_exception_early() and then possibly > ppc_md.handle_hmi_expection(). This is only defined on PowerNV, where > they point to opal_hmi_exception_early() and > opal_handle_hmi_exception() respectively. > > The early exception calls into opal through opal_handle_hmi, which is an > OPAL call (OPAL_HANDLE_HMI). skiboot/core/hmi.c lists the contents of > the HMER (Hypervisor Maintenance Exception Register), which identifies > the actual cause of the HMI. You can find the list in the skiboot repo > on github, including the action that will be taken: > https://github.com/open-power/skiboot/blob/master/core/hmi.c > The rest of the file fleshes out the mechanics of HMIs: for example, > where they are caused by the failure of a POWER8 co-processor such as > CAPI or NX. > > Some HMIs are relayed by Skiboot to Linux by sending an OPAL_MSG_HMI_EVT > to Linux. This triggers off some further processing which causes a > message to be printed in dmesg. The relevant file here is > platforms/powernv/opal-hmi.c > > The script, therefore, is useful because: > - HMIs are an exceptional/error condition that is not hit in normal > operation. Indeed, without the xscom commands in this script > (or a CAPI card), it's almost impossible to hit them. > - HMIs involve communications between Skiboot and Linux, involve > touching the PACA, and generally work in an area that is prone to > bugs, so testing them is especially valuable. > - The script is carefully calibrated to send HMIs that trigger a > message in dmesg but which don't checkstop the machine. > > To answer your final question, I'm not entirely sure if HMIs are POWER8 > specific. I suspect they've been around for a lot longer, but maybe > someone who's been around IBM chips for longer than me could clarify this.
Adding this to doc/ somewhere in kernel and/or skiboot would be great. There's a skiboot doc/hmi.txt that's begging for a patch, you know, creating it :) _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
