linux-kernel - Re: [PATCH] coresight-tmc: Add configurable timeout for flush and tmcready

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Message-ID: <78f2179d-26c2-47f0-bc19-b72e5e51ad29@linaro.org>
Date: Fri, 27 Jun 2025 12:23:29 +0100
From: James Clark <james.clark@...aro.org>
To: Yuanfang Zhang <quic_yuanfang@...cinc.com>,
 Suzuki K Poulose <suzuki.poulose@....com>, Mike Leach
 <mike.leach@...aro.org>, Leo Yan <leo.yan@....com>
Cc: kernel@....qualcomm.com, coresight@...ts.linaro.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Subject: Re: [PATCH] coresight-tmc: Add configurable timeout for flush and
 tmcready



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@...cinc.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,