Re: [PATCH 1/2] coresight: Set affinity to invalid for missing CPU phandle

From: Suzuki K Poulose
Date: Thu Jun 20 2019 - 10:00:39 EST


Thanks for the patch. Please could you change the subject to :

"coresight: Do not default to CPU0 for missing CPU phandle"

On 20/06/2019 14:45, Sai Prakash Ranjan wrote:
Affinity defaults to CPU0 in case of missing CPU phandle
and this leads to crashes in some cases because of such
wrong assumption. Fix this by returning -ENODEV in

Thats not the right justification. Causing crashes is due to
bad DT/firmware. I would be happy with something like :

"Coresight platform support assumes that a missing \"cpu\" phandle
defaults to CPU0. This could be problematic and unnecessarily binds
components to CPU0, where they may not be. Let us make the DT binding
rules a bit stricter by not defaulting to CPU0 for missing "cpu"
affinity information."

Also, you must

1) update the devicetree/bindings document to reflect the same.
2) update the drivers to take appropriate action on the missing CPU
where they are expected (e.g, CPU-debug, etm*), to prevent
breaking a bisect.

coresight platform for such cases and then handle it
in the coresight drivers.

Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>
drivers/hwtracing/coresight/coresight-platform.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-platform.c b/drivers/hwtracing/coresight/coresight-platform.c
index 3c5ceda8db24..b1ea60c210e1 100644
--- a/drivers/hwtracing/coresight/coresight-platform.c
+++ b/drivers/hwtracing/coresight/coresight-platform.c
@@ -160,15 +160,17 @@ static int of_coresight_get_cpu(struct device *dev)
if (!dev->of_node)
return 0;
dn = of_parse_phandle(dev->of_node, "cpu", 0);
- /* Affinity defaults to CPU0 */
+ /* Affinity defaults to invalid if no cpu nodes are found*/

The code is self explanatory here. You could drop the comment.

if (!dn)
- return 0;
+ return -ENODEV;
cpu = of_cpu_node_to_id(dn);
- /* Affinity to CPU0 if no cpu nodes are found */
- return (cpu < 0) ? 0 : cpu;
+ return cpu;