[Skiboot] [PATCH v2 5/5] hw/phb4: Update some comments
oohall at gmail.com
Thu Jan 31 18:15:45 AEDT 2019
I now know what an IODA cache is and I'm not happy about it. With
the power of Comments™ you too can share the misery.
Signed-off-by: Oliver O'Halloran <oohall at gmail.com>
hw/phb4.c | 31 ++++++++++++-------------------
1 file changed, 12 insertions(+), 19 deletions(-)
diff --git a/hw/phb4.c b/hw/phb4.c
index 9ece0f05cd41..216915da99b4 100644
@@ -898,30 +898,23 @@ static uint64_t phb4_default_mbt0(struct phb4 *p, unsigned int bar_idx)
-/* Clear IODA cache tables */
+ * Clear the saved (cached) IODA state.
+ * The caches here are used to save the configuration of the IODA tables
+ * done by the OS. When the PHB is reset it loses all of its internal state
+ * so we need to keep a copy to restore from.
static void phb4_init_ioda_cache(struct phb4 *p)
- * RTT and PELTV. RTE should be 0xFF's to indicate
- * invalid PE# for the corresponding RID.
- * Note: Instead we set all RTE entries to 0x00 to
- * work around a problem where PE lookups might be
- * done before Linux has established valid PE's
- * (during PCI probing). We can revisit that once/if
- * Linux has been fixed to always setup valid PEs.
- * The value 0x00 corresponds to the default PE# Linux
- * uses to check for config space freezes before it
- * has assigned PE# to busses.
- * WARNING: Additionally, we need to be careful, there's
- * a HW issue, if we get an MSI on an RTT entry that is
- * FF, things will go bad. We need to ensure we don't
- * ever let a live FF RTT even temporarily when resetting
- * for EEH etc... (HW278969).
+ * The RTT entries (RTE) are supposed to be initialised to
+ * 0xFF which indicates an invalid PE# for that RTT index
+ * (the bdfn). However, we set them to 0x00 since Linux
+ * needs to find the devices first by scanning config space
+ * and this occurs before PEs have been assigned.
for (i = 0; i < RTT_TABLE_ENTRIES; i++)
p->tbl_rtt[i] = PHB4_RESERVED_PE_NUM(p);
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