powerpc/powernv: define a standard delay for OPAL_BUSY type retry loops

[ Upstream commit 34dd25de9fe3f60bfdb31b473bf04b28262d0896 ]

This is the start of an effort to tidy up and standardise all the
delays. Existing loops have a range of delay/sleep periods from 1ms
to 20ms, and some have no delay. They all loop forever except rtc,
which times out after 10 retries, and that uses 10ms delays. So use
10ms as our standard delay. The OPAL maintainer agrees 10ms is a
reasonable starting point.

The idea is to use the same recipe everywhere, once this is proven to
work then it will be documented as an OPAL API standard. Then both
firmware and OS can agree, and if a particular call needs something
else, then that can be documented with reasoning.

This is not the end-all of this effort, it's just a relatively easy
change that fixes some existing high latency delays. There should be
provision for standardising timeouts and/or interruptible loops where
possible, so non-fatal firmware errors don't cause hangs.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>

diff --git a/arch/powerpc/include/asm/opal.h b/arch/powerpc/include/asm/opal.h
index 042af1abfc4dd02a5f0902bd41b7e67237bfdfbd..e1b164f4a8f07c5edb1bc5f32baa9bfd23824f8a 100644 (file)
--- a/arch/powerpc/include/asm/opal.h
+++ b/arch/powerpc/include/asm/opal.h
@@ -21,6 +21,9 @@
 /* We calculate number of sg entries based on PAGE_SIZE */
 #define SG_ENTRIES_PER_NODE ((PAGE_SIZE - 16) / sizeof(struct opal_sg_entry))
 
+/* Default time to sleep or delay between OPAL_BUSY/OPAL_BUSY_EVENT loops */
+#define OPAL_BUSY_DELAY_MS     10
+
 /* /sys/firmware/opal */
 extern struct kobject *opal_kobj;