Re: [PATCH v2 2/2] ACPI/PPTT: Handle architecturally unknown cache types

From: Jeffrey Hugo
Date: Mon Sep 17 2018 - 18:46:32 EST

On 9/17/2018 10:17 AM, Sudeep Holla wrote:

On 14/09/18 17:28, Jeffrey Hugo wrote:
The type of a cache might not be specified by architectural mechanisms (ie
system registers), but its type might be specified in the PPTT. In this
case, we should populate the type of the cache, rather than leave it

This fixes the issue where the cacheinfo driver will not populate sysfs
for such caches, resulting in the information missing from utilities like
lstopo and lscpu, thus degrading the user experience.

Fixes: 2bd00bcd73e5 (ACPI/PPTT: Add Processor Properties Topology Table parsing)
Reported-by: Vijaya Kumar K <vkilari@xxxxxxxxxxxxxx>
Signed-off-by: Jeffrey Hugo <jhugo@xxxxxxxxxxxxxx>
drivers/acpi/pptt.c | 15 +++++++++++----
1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
index d1e26cb..bb00ed9 100644
--- a/drivers/acpi/pptt.c
+++ b/drivers/acpi/pptt.c
@@ -402,11 +402,18 @@ static void update_cache_properties(struct cacheinfo *this_leaf,
- * If the above flags are valid, and the cache type is NOCACHE
- * update the cache type as well.
+ * If cache type is NOCACHE, then the cache hasn't been specified
+ * via other mechanisms. Update the type if either the cache has
+ * been fully specified in PPTT, or a cache type has been provided.
+ *
+ * Note, we assume such caches are unified based on conventional system
+ * design and known examples. Significant work is required elsewhere to
+ * fully support data/instruction only type caches which are only
+ * specified in PPTT.
- if (this_leaf->type == CACHE_TYPE_NOCACHE &&
+ if ((this_leaf->type == CACHE_TYPE_NOCACHE) &&
+ (valid_flags == PPTT_CHECKED_ATTRIBUTES ||
+ found_cache->flags & ACPI_PPTT_CACHE_TYPE_VALID))
this_leaf->type = CACHE_TYPE_UNIFIED;

I thought I did mention that we can drop the valid_flags altogether
unless Jeremy has reasons not to.

You suggested that perhaps that could be the case. It seemed like an open question to me. I'm at Linaro Connect without access to the device this week, so I guess someone has roughly a week to chime in that the valid flags should be kept, otherwise I'll try a v3 with them removed.

Jeffrey Hugo
Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.