linux-kernel - [PATCH v2 12/12] coresight: tmc: Add configuration support for trace buffer size

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Date:   Tue, 29 May 2018 14:15:37 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     linux-arm-kernel@...ts.infradead.org
Cc:     linux-kernel@...r.kernel.org, mathieu.poirier@...aro.org,
        mike.leach@...aro.org, robert.walker@....com,
        coresight@...ts.linaro.org, devicetree@...r.kernel.org,
        robh@...nel.org, frowand.list@...il.com,
        Suzuki K Poulose <suzuki.poulose@....com>
Subject: [PATCH v2 12/12] coresight: tmc: Add configuration support for trace buffer size

Now that we can dynamically switch between contiguous memory and
SG table depending on the trace buffer size, provide the support
for selecting an appropriate buffer size.

Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
---
 .../ABI/testing/sysfs-bus-coresight-devices-tmc    |  8 ++++++
 .../devicetree/bindings/arm/coresight.txt          |  3 +-
 drivers/hwtracing/coresight/coresight-tmc.c        | 33 ++++++++++++++++++++++
 3 files changed, 43 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/testing/sysfs-bus-coresight-devices-tmc b/Documentation/ABI/testing/sysfs-bus-coresight-devices-tmc
index 4fe677e..ea78714 100644
--- a/Documentation/ABI/testing/sysfs-bus-coresight-devices-tmc
+++ b/Documentation/ABI/testing/sysfs-bus-coresight-devices-tmc
@@ -83,3 +83,11 @@ KernelVersion:	4.7
 Contact:	Mathieu Poirier <mathieu.poirier@...aro.org>
 Description:	(R) Indicates the capabilities of the Coresight TMC.
 		The value is read directly from the DEVID register, 0xFC8,
+
+What:		/sys/bus/coresight/devices/<memory_map>.tmc/buffer_size
+Date:		August 2018
+KernelVersion:	4.18
+Contact:	Mathieu Poirier <mathieu.poirier@...aro.org>
+Description:	(RW) Size of the trace buffer for TMC-ETR when used in SYSFS
+		mode. Writable only for TMC-ETR configurations. The value
+		should be aligned to the kernel pagesize.
diff --git a/Documentation/devicetree/bindings/arm/coresight.txt b/Documentation/devicetree/bindings/arm/coresight.txt
index 603d3c6..9aa30a1 100644
--- a/Documentation/devicetree/bindings/arm/coresight.txt
+++ b/Documentation/devicetree/bindings/arm/coresight.txt
@@ -84,7 +84,8 @@ its hardware characteristcs.
 * Optional property for TMC:
 
 	* arm,buffer-size: size of contiguous buffer space for TMC ETR
-	 (embedded trace router)
+	  (embedded trace router). This property is obsolete. The buffer size
+	  can be configured dynamically via buffer_size property in sysfs.
 
 	* arm,scatter-gather: boolean. Indicates that the TMC-ETR can safely
 	  use the SG mode on this system.
diff --git a/drivers/hwtracing/coresight/coresight-tmc.c b/drivers/hwtracing/coresight/coresight-tmc.c
index bc8fc86..1b817ec 100644
--- a/drivers/hwtracing/coresight/coresight-tmc.c
+++ b/drivers/hwtracing/coresight/coresight-tmc.c
@@ -277,8 +277,41 @@ static ssize_t trigger_cntr_store(struct device *dev,
 }
 static DEVICE_ATTR_RW(trigger_cntr);
 
+static ssize_t buffer_size_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
+{
+	struct tmc_drvdata *drvdata = dev_get_drvdata(dev->parent);
+
+	return sprintf(buf, "%#x\n", drvdata->size);
+}
+
+static ssize_t buffer_size_store(struct device *dev,
+				 struct device_attribute *attr,
+				 const char *buf, size_t size)
+{
+	int ret;
+	unsigned long val;
+	struct tmc_drvdata *drvdata = dev_get_drvdata(dev->parent);
+
+	/* Only permitted for TMC-ETRs */
+	if (drvdata->config_type != TMC_CONFIG_TYPE_ETR)
+		return -EPERM;
+
+	ret = kstrtoul(buf, 0, &val);
+	if (ret)
+		return ret;
+	/* The buffer size should be page aligned */
+	if (val & (PAGE_SIZE - 1))
+		return -EINVAL;
+	drvdata->size = val;
+	return size;
+}
+
+static DEVICE_ATTR_RW(buffer_size);
+
 static struct attribute *coresight_tmc_attrs[] = {
 	&dev_attr_trigger_cntr.attr,
+	&dev_attr_buffer_size.attr,
 	NULL,
 };
 
-- 
2.7.4