[Skiboot] [PATCH v4 8/9] nest sampling rate workaround

[Madhavan Srinivasan]

HW325868 showed that the default sampling rate used by slw ima microcode
does not fetch any mcs write counter values. After a lot of experiments,
sampling rate of 64ms was found to be effective. Accordingly, set the new sample
rate before starting the engine.

Signed-off-by: Madhavan Srinivasan <maddy at linux.vnet.ibm.com>
---
 hw/nest.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/hw/nest.c b/hw/nest.c
index a45bbae8fe81..7067b5a84efb 100644
--- a/hw/nest.c
+++ b/hw/nest.c
@@ -389,6 +389,15 @@ void nest_pmu_init(int loaded)
 		addr = chip->homer_base + SLW_IMA_OFFSET;
 		dt_add_property_u64(chip_dev, "offset", addr);
 		dt_add_property_u64(chip_dev, "size", SLW_IMA_SIZE);
+
+		/*
+		 * Work around for HW325868: modify the sampling rate
+		 * since the default sampling rate of 128us does not
+		 * fetch any mcs write data. Update the new sampling rate
+		 * of 64ms before starting the engine.
+		 */
+		addr = chip->homer_base + CB_STRUCT_SPEED;
+		out_be64((u64 *)addr, SLW_IMA_SAMPLE_RATE_64MS);
 	}
 
 	/*
-- 
1.9.1