From: Yeoreum Yun <yeoreum.yun@arm.com>
To: James Clark <james.clark@linaro.org>
Cc: suzuki.poulose@arm.com, coresight@lists.linaro.org,
mike.leach@linaro.org,
Alexander Shishkin <alexander.shishkin@linux.intel.com>,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] coresight: Drop atomics in connection refcounts
Date: Thu, 5 Dec 2024 10:10:38 +0000 [thread overview]
Message-ID: <Z1F8HvLY/04jukUH@e129823.arm.com> (raw)
In-Reply-To: <20241128121414.2425119-1-james.clark@linaro.org>
This patch looks good to me.
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
On Thu, Nov 28, 2024 at 12:14:14PM +0000, James Clark wrote:
> These belong to the device being enabled or disabled and are only ever
> used inside the device's spinlock. Remove the atomics to not imply that
> there are any other concurrent accesses.
>
> If atomics were necessary I don't think they would have been enough
> anyway. There would be nothing to prevent an enable or disable running
> concurrently if not for the spinlock.
>
> Signed-off-by: James Clark <james.clark@linaro.org>
> ---
> drivers/hwtracing/coresight/coresight-funnel.c | 6 +++---
> drivers/hwtracing/coresight/coresight-replicator.c | 6 +++---
> drivers/hwtracing/coresight/coresight-tpda.c | 6 +++---
> include/linux/coresight.h | 4 ++--
> 4 files changed, 11 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-funnel.c b/drivers/hwtracing/coresight/coresight-funnel.c
> index 5a819c8970fb..bd32f74cbdae 100644
> --- a/drivers/hwtracing/coresight/coresight-funnel.c
> +++ b/drivers/hwtracing/coresight/coresight-funnel.c
> @@ -86,14 +86,14 @@ static int funnel_enable(struct coresight_device *csdev,
> bool first_enable = false;
>
> spin_lock_irqsave(&drvdata->spinlock, flags);
> - if (atomic_read(&in->dest_refcnt) == 0) {
> + if (in->dest_refcnt == 0) {
> if (drvdata->base)
> rc = dynamic_funnel_enable_hw(drvdata, in->dest_port);
> if (!rc)
> first_enable = true;
> }
> if (!rc)
> - atomic_inc(&in->dest_refcnt);
> + in->dest_refcnt++;
> spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
> if (first_enable)
> @@ -130,7 +130,7 @@ static void funnel_disable(struct coresight_device *csdev,
> bool last_disable = false;
>
> spin_lock_irqsave(&drvdata->spinlock, flags);
> - if (atomic_dec_return(&in->dest_refcnt) == 0) {
> + if (--in->dest_refcnt == 0) {
> if (drvdata->base)
> dynamic_funnel_disable_hw(drvdata, in->dest_port);
> last_disable = true;
> diff --git a/drivers/hwtracing/coresight/coresight-replicator.c b/drivers/hwtracing/coresight/coresight-replicator.c
> index 3e55be9c8418..31322aea19f2 100644
> --- a/drivers/hwtracing/coresight/coresight-replicator.c
> +++ b/drivers/hwtracing/coresight/coresight-replicator.c
> @@ -126,7 +126,7 @@ static int replicator_enable(struct coresight_device *csdev,
> bool first_enable = false;
>
> spin_lock_irqsave(&drvdata->spinlock, flags);
> - if (atomic_read(&out->src_refcnt) == 0) {
> + if (out->src_refcnt == 0) {
> if (drvdata->base)
> rc = dynamic_replicator_enable(drvdata, in->dest_port,
> out->src_port);
> @@ -134,7 +134,7 @@ static int replicator_enable(struct coresight_device *csdev,
> first_enable = true;
> }
> if (!rc)
> - atomic_inc(&out->src_refcnt);
> + out->src_refcnt++;
> spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
> if (first_enable)
> @@ -180,7 +180,7 @@ static void replicator_disable(struct coresight_device *csdev,
> bool last_disable = false;
>
> spin_lock_irqsave(&drvdata->spinlock, flags);
> - if (atomic_dec_return(&out->src_refcnt) == 0) {
> + if (--out->src_refcnt == 0) {
> if (drvdata->base)
> dynamic_replicator_disable(drvdata, in->dest_port,
> out->src_port);
> diff --git a/drivers/hwtracing/coresight/coresight-tpda.c b/drivers/hwtracing/coresight/coresight-tpda.c
> index bfca103f9f84..4ec676bea1ce 100644
> --- a/drivers/hwtracing/coresight/coresight-tpda.c
> +++ b/drivers/hwtracing/coresight/coresight-tpda.c
> @@ -190,10 +190,10 @@ static int tpda_enable(struct coresight_device *csdev,
> int ret = 0;
>
> spin_lock(&drvdata->spinlock);
> - if (atomic_read(&in->dest_refcnt) == 0) {
> + if (in->dest_refcnt == 0) {
> ret = __tpda_enable(drvdata, in->dest_port);
> if (!ret) {
> - atomic_inc(&in->dest_refcnt);
> + in->dest_refcnt++;
> csdev->refcnt++;
> dev_dbg(drvdata->dev, "TPDA inport %d enabled.\n", in->dest_port);
> }
> @@ -223,7 +223,7 @@ static void tpda_disable(struct coresight_device *csdev,
> struct tpda_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>
> spin_lock(&drvdata->spinlock);
> - if (atomic_dec_return(&in->dest_refcnt) == 0) {
> + if (--in->dest_refcnt == 0) {
> __tpda_disable(drvdata, in->dest_port);
> csdev->refcnt--;
> }
> diff --git a/include/linux/coresight.h b/include/linux/coresight.h
> index c13342594278..834029cb9ba2 100644
> --- a/include/linux/coresight.h
> +++ b/include/linux/coresight.h
> @@ -200,8 +200,8 @@ struct coresight_connection {
> struct coresight_device *dest_dev;
> struct coresight_sysfs_link *link;
> struct coresight_device *src_dev;
> - atomic_t src_refcnt;
> - atomic_t dest_refcnt;
> + int src_refcnt;
> + int dest_refcnt;
> };
>
> /**
> --
> 2.34.1
>
next prev parent reply other threads:[~2024-12-05 10:10 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-11-28 12:14 James Clark
2024-12-05 10:10 ` Yeoreum Yun [this message]
2024-12-11 10:20 ` Suzuki K Poulose
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