[PATCH v11 4/9] coresight: etm3x: fix inconsistencies with sysfs configuration
Mike Leach
mike.leach at arm.com
Fri Sep 18 06:57:30 PDT 2026
Hi,
On 9/15/26 12:34, Yeoreum Yun wrote:
> The current ETM3x configuration via sysfs can lead to the following
> inconsistencies:
>
> - If a configuration is modified via sysfs while a perf session is
> active, the running configuration may differ between before
> a sched-out and after a subsequent sched-in.
>
> To resolve these issues, separate the configuration into:
>
> - active_config: the configuration applied to the current session
> - config: the configuration set via sysfs
>
Same comment as for the etm4 config naming
> Additionally:
>
> - Since active_config and related fields are accessed only by the local CPU
> in etm_enable/disable_sysfs_smp_call() (similar to perf enable/disable),
> remove the lock/unlock from the sysfs enable/disable path and
> starting/dying_cpu path except when to access config fields only.
>
> - Some of sysfs interface read etm register directly. To reduce lock
> scope while the etm_enable_hw()/etm_disable_hw(), handle it via
> IPI so that registers could be read from on proper CPU.
>
> Fixes: 1925a470ce69 ("coresight: etm3x: splitting struct etm_drvdata")
> Signed-off-by: Yeoreum Yun <yeoreum.yun at arm.com>
> ---
> drivers/hwtracing/coresight/coresight-etm.h | 4 +-
> drivers/hwtracing/coresight/coresight-etm3x-core.c | 68 ++++++++++--------
> .../hwtracing/coresight/coresight-etm3x-sysfs.c | 80 +++++++++++++++-------
> 3 files changed, 100 insertions(+), 52 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm.h b/drivers/hwtracing/coresight/coresight-etm.h
> index 1d753cca29439..f3796162168d4 100644
> --- a/drivers/hwtracing/coresight/coresight-etm.h
> +++ b/drivers/hwtracing/coresight/coresight-etm.h
> @@ -226,7 +226,8 @@ struct etm_config {
> * @etmccr: value of register ETMCCR.
> * @etmccer: value of register ETMCCER.
> * @traceid: value of the current ID for this component.
> - * @config: structure holding configuration parameters.
> + * @active_config: structure holding current running configuration.
> + * @config: structure holding sysfs mode configuration.
> */
> struct etm_drvdata {
> struct csdev_access csa;
> @@ -248,6 +249,7 @@ struct etm_drvdata {
> u32 etmccr;
> u32 etmccer;
> u32 traceid;
> + struct etm_config active_config;
> struct etm_config config;
> };
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm3x-core.c b/drivers/hwtracing/coresight/coresight-etm3x-core.c
> index 862ad0786699c..fd76a57e5f861 100644
> --- a/drivers/hwtracing/coresight/coresight-etm3x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm3x-core.c
> @@ -308,7 +308,7 @@ void etm_config_trace_mode(struct etm_config *config)
> static int etm_parse_event_config(struct etm_drvdata *drvdata,
> struct perf_event *event)
> {
> - struct etm_config *config = &drvdata->config;
> + struct etm_config *config = &drvdata->active_config;
> struct perf_event_attr *attr = &event->attr;
> u8 ts_level;
>
> @@ -367,7 +367,7 @@ static int etm_enable_hw(struct etm_drvdata *drvdata)
> {
> int i, rc;
> u32 etmcr;
> - struct etm_config *config = &drvdata->config;
> + struct etm_config *config = &drvdata->active_config;
> struct coresight_device *csdev = drvdata->csdev;
>
> CS_UNLOCK(drvdata->csa.base);
> @@ -442,32 +442,30 @@ static int etm_enable_hw(struct etm_drvdata *drvdata)
> struct etm_enable_arg {
> struct etm_drvdata *drvdata;
> struct coresight_path *path;
> + struct etm_config config;
> int rc;
> };
>
> static void etm_enable_sysfs_smp_call(void *info)
> {
> struct etm_enable_arg *arg = info;
> + struct etm_drvdata *drvdata;
> struct coresight_device *csdev;
>
> if (WARN_ON(!arg))
> return;
>
> - csdev = arg->drvdata->csdev;
> - if (!coresight_take_mode(csdev, CS_MODE_SYSFS)) {
> - /* Someone is already using the tracer */
> - arg->rc = -EBUSY;
> - return;
> - }
> + drvdata = arg->drvdata;
> + csdev = drvdata->csdev;
>
> - arg->rc = etm_enable_hw(arg->drvdata);
> + drvdata->active_config = arg->config;
> + drvdata->traceid = arg->path->trace_id;
>
> - /* The tracer didn't start */
> - if (arg->rc) {
> - coresight_set_mode(csdev, CS_MODE_DISABLED);
> + arg->rc = etm_enable_hw(arg->drvdata);
> + if (arg->rc)
> return;
> - }
>
> + drvdata->sticky_enable = true;
> csdev->path = arg->path;
> }
>
> @@ -512,9 +510,10 @@ static int etm_enable_sysfs(struct coresight_device *csdev, struct coresight_pat
> struct etm_enable_arg arg = { };
> int ret;
>
> - spin_lock(&drvdata->spinlock);
> -
> - drvdata->traceid = path->trace_id;
> + if (!coresight_take_mode(csdev, CS_MODE_SYSFS)) {
> + /* Someone is already using the tracer */
> + return -EBUSY;
> + }
>
> /*
> * Configure the ETM only if the CPU is online. If it isn't online
> @@ -523,23 +522,27 @@ static int etm_enable_sysfs(struct coresight_device *csdev, struct coresight_pat
> if (cpu_online(drvdata->cpu)) {
> arg.drvdata = drvdata;
> arg.path = path;
> +
> + scoped_guard(spinlock, &drvdata->spinlock) {
> + arg.config = drvdata->config;
> + }
> +
Again I think the arg.config is unnecessary
Regards
Mike
> ret = smp_call_function_single(drvdata->cpu,
> etm_enable_sysfs_smp_call, &arg, 1);
> if (!ret)
> ret = arg.rc;
> - if (!ret)
> - drvdata->sticky_enable = true;
> } else {
> ret = -ENODEV;
> }
>
> - if (ret)
> + if (!ret) {
> + dev_dbg(&csdev->dev, "ETM tracing enabled\n");
> + } else {
> etm_release_trace_id(drvdata);
> + /* The tracer didn't start */
> + coresight_set_mode(csdev, CS_MODE_DISABLED);
> + }
>
> - spin_unlock(&drvdata->spinlock);
> -
> - if (!ret)
> - dev_dbg(&csdev->dev, "ETM tracing enabled\n");
> return ret;
> }
>
> @@ -565,7 +568,7 @@ static int etm_enable(struct coresight_device *csdev, struct perf_event *event,
> static void etm_disable_hw(struct etm_drvdata *drvdata)
> {
> int i;
> - struct etm_config *config = &drvdata->config;
> + struct etm_config *config = &drvdata->active_config;
> struct coresight_device *csdev = drvdata->csdev;
>
> CS_UNLOCK(drvdata->csa.base);
> @@ -593,7 +596,6 @@ static void etm_disable_sysfs_smp_call(void *info)
> etm_disable_hw(drvdata);
>
> drvdata->csdev->path = NULL;
> - coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
> }
>
> static void etm_disable_perf(struct coresight_device *csdev)
> @@ -630,8 +632,9 @@ static void etm_disable_perf(struct coresight_device *csdev)
> static void etm_disable_sysfs(struct coresight_device *csdev)
> {
> struct etm_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
> -
> - spin_lock(&drvdata->spinlock);
> + struct etm_config *config = &drvdata->config;
> + const struct etm_config *active_config = &drvdata->active_config;
> + int i;
>
> /*
> * Executing etm_disable_hw on the cpu whose ETM is being disabled
> @@ -640,7 +643,14 @@ static void etm_disable_sysfs(struct coresight_device *csdev)
> smp_call_function_single(drvdata->cpu, etm_disable_sysfs_smp_call,
> drvdata, 1);
>
> - spin_unlock(&drvdata->spinlock);
> + /*
> + * Userspace may read seq_curr_state and cntr_val through sysfs
> + * after the sysfs-session has been disabled.
> + */
> + for (i = 0; i < drvdata->nr_cntr; i++)
> + config->cntr_val[i] = active_config->cntr_val[i];
> +
> + config->seq_curr_state = active_config->seq_curr_state;
>
> /*
> * we only release trace IDs when resetting sysfs.
> @@ -649,6 +659,8 @@ static void etm_disable_sysfs(struct coresight_device *csdev)
> * prior trace id allocation method
> */
>
> + coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
> +
> dev_dbg(&csdev->dev, "ETM tracing disabled\n");
> }
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> index d4846d6364945..2c8c129228589 100644
> --- a/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> +++ b/drivers/hwtracing/coresight/coresight-etm3x-sysfs.c
> @@ -6,10 +6,48 @@
>
> #include <linux/pid_namespace.h>
> #include <linux/pm_runtime.h>
> +#include <linux/smp.h>
> #include <linux/sysfs.h>
> #include "coresight-etm.h"
> #include "coresight-priv.h"
>
> +struct etm_readl_cslocked_arg {
> + struct etm_drvdata *drvdata;
> + u32 off;
> + unsigned long *val;
> +};
> +
> +static void etm_readl_cslocked_smp_call(void *info)
> +{
> + struct etm_readl_cslocked_arg *arg = info;
> +
> + CS_UNLOCK(arg->drvdata->csa.base);
> + *arg->val = etm_readl(arg->drvdata, arg->off);
> + CS_LOCK(arg->drvdata->csa.base);
> +}
> +
> +static int etm_readl_cslocked(struct etm_drvdata *drvdata, u32 off,
> + unsigned long *val)
> +{
> + int ret;
> + struct etm_readl_cslocked_arg arg;
> +
> + ret = pm_runtime_get_sync(drvdata->csdev->dev.parent);
> + if (ret < 0)
> + goto out;
> +
> + arg.drvdata = drvdata;
> + arg.off = off;
> + arg.val = val;
> +
> + ret = smp_call_function_single(drvdata->cpu,
> + etm_readl_cslocked_smp_call,
> + (void *)&arg, 1);
> +out:
> + pm_runtime_put(drvdata->csdev->dev.parent);
> + return ret;
> +}
> +
> static ssize_t nr_addr_cmp_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> @@ -45,18 +83,13 @@ static DEVICE_ATTR_RO(nr_ctxid_cmp);
> static ssize_t etmsr_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> - unsigned long flags, val;
> + int ret;
> + unsigned long val;
> struct etm_drvdata *drvdata = dev_get_drvdata(dev->parent);
>
> - pm_runtime_get_sync(dev->parent);
> - spin_lock_irqsave(&drvdata->spinlock, flags);
> - CS_UNLOCK(drvdata->csa.base);
> -
> - val = etm_readl(drvdata, ETMSR);
> -
> - CS_LOCK(drvdata->csa.base);
> - spin_unlock_irqrestore(&drvdata->spinlock, flags);
> - pm_runtime_put(dev->parent);
> + ret = etm_readl_cslocked(drvdata, ETMSR, &val);
> + if (ret)
> + return ret;
>
> return sprintf(buf, "%#lx\n", val);
> }
> @@ -74,7 +107,7 @@ static ssize_t reset_store(struct device *dev,
> ret = kstrtoul(buf, 16, &val);
> if (ret)
> return ret;
> - if (coresight_get_mode(drvdata->csdev))
> + if (coresight_get_mode(drvdata->csdev) == CS_MODE_SYSFS)
> return -EBUSY;
>
> if (val) {
> @@ -719,7 +752,9 @@ static DEVICE_ATTR_RW(cntr_rld_event);
> static ssize_t cntr_val_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> + int ret;
> u32 val;
> + unsigned long val2;
> struct etm_drvdata *drvdata = dev_get_drvdata(dev->parent);
> struct etm_config *config = &drvdata->config;
>
> @@ -728,7 +763,10 @@ static ssize_t cntr_val_show(struct device *dev,
> val = config->cntr_val[config->cntr_idx];
> spin_unlock(&drvdata->spinlock);
> } else {
> - val = etm_readl(drvdata, ETMCNTVRn(config->cntr_idx));
> + ret = etm_readl_cslocked(drvdata, ETMCNTVRn(config->cntr_idx), &val2);
> + if (ret)
> + return ret;
> + val = val2;
> }
>
> return sysfs_emit(buf, "%#x\n", val);
> @@ -746,7 +784,7 @@ static ssize_t cntr_val_store(struct device *dev,
> ret = kstrtoul(buf, 16, &val);
> if (ret)
> return ret;
> - if (coresight_get_mode(drvdata->csdev))
> + if (coresight_get_mode(drvdata->csdev) == CS_MODE_SYSFS)
> return -EBUSY;
>
> spin_lock(&drvdata->spinlock);
> @@ -934,7 +972,8 @@ static DEVICE_ATTR_RW(seq_13_event);
> static ssize_t seq_curr_state_show(struct device *dev,
> struct device_attribute *attr, char *buf)
> {
> - unsigned long val, flags;
> + int ret;
> + unsigned long val;
> struct etm_drvdata *drvdata = dev_get_drvdata(dev->parent);
> struct etm_config *config = &drvdata->config;
>
> @@ -943,15 +982,10 @@ static ssize_t seq_curr_state_show(struct device *dev,
> goto out;
> }
>
> - pm_runtime_get_sync(dev->parent);
> - spin_lock_irqsave(&drvdata->spinlock, flags);
> -
> - CS_UNLOCK(drvdata->csa.base);
> - val = (etm_readl(drvdata, ETMSQR) & ETM_SQR_MASK);
> - CS_LOCK(drvdata->csa.base);
> -
> - spin_unlock_irqrestore(&drvdata->spinlock, flags);
> - pm_runtime_put(dev->parent);
> + ret = etm_readl_cslocked(drvdata, ETMSQR, &val);
> + if (ret)
> + return ret;
> + val &= ETM_SQR_MASK;
> out:
> return sprintf(buf, "%#lx\n", val);
> }
>
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