Messages in this thread | | | Date | Tue, 20 Sep 2022 17:11:34 +0100 | From | Jonathan Cameron <> | Subject | Re: [RFC PATCH 6/9] cxl/mem: Trace Memory Module Event Record |
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On Wed, 14 Sep 2022 14:17:14 -0700 Ira Weiny <ira.weiny@intel.com> wrote:
> On Thu, Aug 25, 2022 at 11:58:42AM +0100, Jonathan Cameron wrote: > > On Fri, 12 Aug 2022 22:32:40 -0700 > > ira.weiny@intel.com wrote: > > > > > From: Ira Weiny <ira.weiny@intel.com> > > > > > > CXL v3.0 section 8.2.9.2.1.3 defines the Memory Module Event Record. > > > > > > Determine if the event read is memory module record and if so trace the > > > record. > > > > > > Signed-off-by: Ira Weiny <ira.weiny@intel.com> > > Similar comments to on previous patches around using > > get_unaligned_le*() > > Yep... > > [snip] > > > > > > > +/* > > > + * Get Health Info Record > > > + * CXL v3.0 section 8.2.9.8.3.1; Table 8-100 > > > + */ > > > +struct cxl_get_health_info { > > > + u8 health_status; > > > + u8 media_status; > > > + u8 add_status; > > > + u8 life_used; > > > + u16 device_temp; > > > > As previous - even though they aren't aligned, I'd have thought > > __le16 etc will still work. The unaligned accessors are fine > > taking __le16 * for example. > > Ok my bad on using u16 here and I will change it. I 100% agree that these > should be __le16/__le32. That said there is no need to use the unaligned > accessors for the 16/32 bit fields. > > The unaligned accessors cast the pointer to a __le16/__le32 type and no > architecture redefines those. So using le{16,32}_to_cpu() should work just > fine on all archs.
If they are unaligned, make sure to use the unaligned accessors.
Key is that it's not a simple cast, but rather a cast to a packed structure. The C spec guarantees that those will be handled correctly even on platforms that don't do unaligned accesses - it will have to use multiple instructions to construct the unaligned access from a set of small aligned ones. The C Spec doesn't guarantee the same for a simple cast to an __le16.
There are some hints on this in: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/include/asm-generic/unaligned.h?id=778aaefb8e864fc61f850539ea479554dd4caea1
I recall a full explanation of why this worked, but no idea where to find that now - might be the thread referred to in that patch from Arnd.
Jonathan
> > [snip] > > > > + > > > + TP_fast_assign( > > > + /* Common */ > > > + __assign_str(dev_name, dev_name); > > > + memcpy(__entry->id, &rec->hdr.id, UUID_SIZE); > > > + __entry->log = log; > > > + __entry->flags = le32_to_cpu(rec->hdr.flags_length) >> 8; > > > + __entry->handle = le16_to_cpu(rec->hdr.handle); > > > + __entry->related_handle = le16_to_cpu(rec->hdr.related_handle); > > > + __entry->timestamp = le64_to_cpu(rec->hdr.timestamp); > > > + > > > + /* Memory Module Event */ > > > + __entry->event_type = rec->event_type; > > > + > > > + /* Device Health Info */ > > > + __entry->health_status = rec->info.health_status; > > > + __entry->media_status = rec->info.media_status; > > > + __entry->life_used = rec->info.life_used; > > > + __entry->dirty_shutdown_cnt = le32_to_cpu(rec->info.dirty_shutdown_cnt); > > > + __entry->cor_vol_err_cnt = le32_to_cpu(rec->info.cor_vol_err_cnt); > > > > I've lost track, but my guess is some / all of these need the unaligned_get_le32() > > etc rather than aligned form. Maybe just be lazy and use the unaligned versions > > even when things happen to be aligned - then we don't have to think about it > > when reviewing :) > > See above. I think the 16/32 bit fields work as intended except for my lack of > using the correct type. > > Ira
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