On 27/06/2025 12:10 pm, Yuanfang Zhang wrote:

The current implementation uses a fixed timeout via coresight_timeout(), which may be insufficient when multiple sources are enabled or under heavy load, leading to TMC readiness or flush completion timeout.

This patch introduces a configurable timeout mechanism for flush and tmcready.

What kind of values are you using? Is there a reason to not increase the global one?

I don't think it's important what value we choose because it's only to stop hangs and make it terminate eventually. As far as I can see it wouldn't matter if we set it to a huge value like 1 second. That would only cause a big delay when something has actually gone wrong. Under normal circumstances the timeout won't be hit so it doesn't really need to be configurable.

Signed-off-by: Yuanfang Zhang quic_yuanfang@quicinc.com

drivers/hwtracing/coresight/coresight-tmc-core.c | 43 ++++++++++++++++++++++-- 1 file changed, 41 insertions(+), 2 deletions(-)

diff --git a/drivers/hwtracing/coresight/coresight-tmc-core.c b/drivers/hwtracing/coresight/coresight-tmc-core.c index 88afb16bb6bec395ba535155228d176250f38625..286d56ce88fe80fbfa022946dc798f0f4e72f961 100644 --- a/drivers/hwtracing/coresight/coresight-tmc-core.c +++ b/drivers/hwtracing/coresight/coresight-tmc-core.c @@ -8,6 +8,7 @@ #include <linux/kernel.h> #include <linux/init.h> #include <linux/types.h> +#include <linux/delay.h> #include <linux/device.h> #include <linux/idr.h> #include <linux/io.h> @@ -35,13 +36,31 @@ DEFINE_CORESIGHT_DEVLIST(etb_devs, "tmc_etb"); DEFINE_CORESIGHT_DEVLIST(etf_devs, "tmc_etf"); DEFINE_CORESIGHT_DEVLIST(etr_devs, "tmc_etr"); +static u32 tmc_timeout;

+static void tmc_extend_timeout(struct csdev_access *csa, u32 offset, int pos, int val) +{

• int i;
• for (i = tmc_timeout; i > 0; i--) {

• if (i - 1)
  

I didn't get what the if is for here? Removing it does basically the same thing, but if you do want to keep it maybe if (i > 1) is more explanatory.

• 	udelay(1);
  

Can you not do udelay(tmc_timeout)?

• }

+}

+static int tmc_wait_status(struct csdev_access *csa, u32 offset, int pos, int val) +{

• return coresight_timeout_action(csa, offset, pos, val,

• 	tmc_extend_timeout);
  

+}

• int tmc_wait_for_tmcready(struct tmc_drvdata *drvdata) { struct coresight_device *csdev = drvdata->csdev; struct csdev_access *csa = &csdev->access;

/* Ensure formatter, unformatter and hardware fifo are empty */

• if (coresight_timeout(csa, TMC_STS, TMC_STS_TMCREADY_BIT, 1)) {

• if (tmc_wait_status(csa, TMC_STS, TMC_STS_TMCREADY_BIT, 1)) { dev_err(&csdev->dev, "timeout while waiting for TMC to be Ready\n"); return -EBUSY;

@@ -61,7 +80,7 @@ void tmc_flush_and_stop(struct tmc_drvdata *drvdata) ffcr |= BIT(TMC_FFCR_FLUSHMAN_BIT); writel_relaxed(ffcr, drvdata->base + TMC_FFCR); /* Ensure flush completes */

• if (coresight_timeout(csa, TMC_FFCR, TMC_FFCR_FLUSHMAN_BIT, 0)) {

• if (tmc_wait_status(csa, TMC_FFCR, TMC_FFCR_FLUSHMAN_BIT, 0)) { dev_err(&csdev->dev, "timeout while waiting for completion of Manual Flush\n"); }

@@ -561,11 +580,31 @@ static ssize_t stop_on_flush_store(struct device *dev, static DEVICE_ATTR_RW(stop_on_flush); +static ssize_t timeout_cfg_show(struct device *dev,

• 		struct device_attribute *attr, char *buf)
  

+{

• return scnprintf(buf, PAGE_SIZE, "%d\n", tmc_timeout);

+}

+static ssize_t timeout_cfg_store(struct device *dev,

• 		 struct device_attribute *attr,
  

• 		 const char *buf, size_t size)
  

+{

• unsigned long val;
• if (kstrtoul(buf, 0, &val))

• return -EINVAL;
  

• tmc_timeout = val;
• return size;

+} +static DEVICE_ATTR_RW(timeout_cfg);

Seeing as the existing timeout is global for all devices, if we do want a configurable one shouldn't we make the global one configurable rather than per-device? That seems too fine grained to me.

static struct attribute *coresight_tmc_attrs[] = { &dev_attr_trigger_cntr.attr, &dev_attr_buffer_size.attr, &dev_attr_stop_on_flush.attr,

• &dev_attr_timeout_cfg.attr, NULL, };

---

base-commit: 408c97c4a5e0b634dcd15bf8b8808b382e888164 change-id: 20250627-flush_timeout-a598b4c0ce7b

Best regards,