interconnect: Revert to previous config if any request fails

This change “interconnect: Revert to previous config if any request fails” in Linux kernel is authored by Georgi Djakov <georgi.djakov [at] linaro.org> on Wed Jan 16 18:11:03 2019 +0200.

interconnect: Revert to previous config if any request fails

When consumers report their bandwidth needs with icc_set_bw(), it's
possible that the requested amount of bandwidth is not available or just
the new configuration fails to apply on some path. In this case revert to
the previous configuration and propagate the error back to the consumers
to let them know that bandwidth is not available, hardware is busy or
whatever error is returned by the interconnect platform driver.

Signed-off-by: Georgi Djakov <georgi.djakov@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

This Linux change may have been applied to various maintained Linux releases and you can find Linux releases including commit dce6d40.

There are 17 lines of Linux source code added/deleted in this change. Code changes to Linux kernel are as follows.

 drivers/interconnect/core.c | 17 +++++++++++++++--
 1 file changed, 15 insertions(+), 2 deletions(-)

diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
index 8091d99..6005a1c 100644
--- a/drivers/interconnect/core.c
+++ b/drivers/interconnect/core.c
@@ -414,14 +414,18 @@ struct icc_path *of_icc_get(struct device *dev, const char *name)
 int icc_set_bw(struct icc_path *path, u32 avg_bw, u32 peak_bw)
 {
 	struct icc_node *node;
+	u32 old_avg, old_peak;
 	size_t i;
 	int ret;
 
-	if (!path)
+	if (!path || !path->num_nodes)
 		return 0;
 
 	mutex_lock(&icc_lock);
 
+	old_avg = path->reqs[0].avg_bw;
+	old_peak = path->reqs[0].peak_bw;
+
 	for (i = 0; i < path->num_nodes; i++) {
 		node = path->reqs[i].node;
 
@@ -434,10 +438,19 @@ int icc_set_bw(struct icc_path *path, u32 avg_bw, u32 peak_bw)
 	}
 
 	ret = apply_constraints(path);
-	if (ret)
+	if (ret) {
 		pr_debug("interconnect: error applying constraints (%d)n",
 			 ret);
 
+		for (i = 0; i < path->num_nodes; i++) {
+			node = path->reqs[i].node;
+			path->reqs[i].avg_bw = old_avg;
+			path->reqs[i].peak_bw = old_peak;
+			aggregate_requests(node);
+		}
+		apply_constraints(path);
+	}
+
 	mutex_unlock(&icc_lock);
 
 	return ret;

The commit for this change in Linux stable tree is dce6d40 (patch).

Leave a Reply

Your email address will not be published. Required fields are marked *