coresight: tmc: Make etr buffer mode user configurable from sysfs

Currently TMC-ETR automatically selects the buffer mode from all available
methods in the following sequentially fallback manner - also in that order.

1. FLAT mode with or without IOMMU
2. TMC-ETR-SG (scatter gather) mode when available
3. CATU mode when available

But this order might not be ideal for all situations. For example if there
is a CATU connected to ETR, it may be better to use TMC-ETR scatter gather
method, rather than CATU. But hard coding such order changes will prevent
us from testing or using a particular mode. This change provides following
new sysfs tunables for the user to control TMC-ETR buffer mode explicitly,
if required. This adds following new sysfs files for buffer mode selection
purpose explicitly in the user space.

/sys/bus/coresight/devices/tmc_etr<N>/buf_modes_available
/sys/bus/coresight/devices/tmc_etr<N>/buf_mode_preferred

$ cat buf_modes_available
auto flat tmc-sg catu	------------------> Supported TMC-ETR buffer modes

$ echo catu > buf_mode_preferred   -------> Explicit buffer mode request

But explicit user request has to be within supported ETR buffer modes only.
These sysfs interface files are exclussive to ETR, and hence these are not
available for other TMC devices such as ETB or ETF etc.

A new auto' mode (i.e ETR_MODE_AUTO) has been added to help fallback to the
existing default behaviour, when user provided preferred buffer mode fails.
ETR_MODE_FLAT and ETR_MODE_AUTO are always available as preferred modes.

Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: James Clark <james.clark@arm.com>
Cc: Leo Yan <leo.yan@linaro.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: coresight@lists.linaro.org
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
[Fixup year in sysfs ABI documentation]
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20230818082112.554638-1-anshuman.khandual@arm.com

1 files changed, 13 insertions, 2 deletions

diff --git a/drivers/hwtracing/coresight/coresight-tmc-core.c b/drivers/hwtracing/coresight/coresight-tmc-core.c
index c106d142e632..7ec5365e2b64 100644
--- a/drivers/hwtracing/coresight/coresight-tmc-core.c
+++ b/drivers/hwtracing/coresight/coresight-tmc-core.c
@@ -10,6 +10,7 @@
 #include <linux/device.h>
 #include <linux/idr.h>
 #include <linux/io.h>
+#include <linux/iommu.h>
 #include <linux/err.h>
 #include <linux/fs.h>
 #include <linux/miscdevice.h>
@@ -344,7 +345,14 @@ static const struct attribute_group coresight_tmc_mgmt_group = {
 	.name = "mgmt",
 };
 
-static const struct attribute_group *coresight_tmc_groups[] = {
+static const struct attribute_group *coresight_etf_groups[] = {
+	&coresight_tmc_group,
+	&coresight_tmc_mgmt_group,
+	NULL,
+};
+
+static const struct attribute_group *coresight_etr_groups[] = {
+	&coresight_etr_group,
 	&coresight_tmc_group,
 	&coresight_tmc_mgmt_group,
 	NULL,
@@ -465,6 +473,7 @@ static int tmc_probe(struct amba_device *adev, const struct amba_id *id)
 	drvdata->memwidth = tmc_get_memwidth(devid);
 	/* This device is not associated with a session */
 	drvdata->pid = -1;
+	drvdata->etr_mode = ETR_MODE_AUTO;
 
 	if (drvdata->config_type == TMC_CONFIG_TYPE_ETR) {
 		drvdata->size = tmc_etr_get_default_buffer_size(dev);
@@ -474,16 +483,17 @@ static int tmc_probe(struct amba_device *adev, const struct amba_id *id)
 	}
 
 	desc.dev = dev;
-	desc.groups = coresight_tmc_groups;
 
 	switch (drvdata->config_type) {
 	case TMC_CONFIG_TYPE_ETB:
+		desc.groups = coresight_etf_groups;
 		desc.type = CORESIGHT_DEV_TYPE_SINK;
 		desc.subtype.sink_subtype = CORESIGHT_DEV_SUBTYPE_SINK_BUFFER;
 		desc.ops = &tmc_etb_cs_ops;
 		dev_list = &etb_devs;
 		break;
 	case TMC_CONFIG_TYPE_ETR:
+		desc.groups = coresight_etr_groups;
 		desc.type = CORESIGHT_DEV_TYPE_SINK;
 		desc.subtype.sink_subtype = CORESIGHT_DEV_SUBTYPE_SINK_SYSMEM;
 		desc.ops = &tmc_etr_cs_ops;
@@ -496,6 +506,7 @@ static int tmc_probe(struct amba_device *adev, const struct amba_id *id)
 		dev_list = &etr_devs;
 		break;
 	case TMC_CONFIG_TYPE_ETF:
+		desc.groups = coresight_etf_groups;
 		desc.type = CORESIGHT_DEV_TYPE_LINKSINK;
 		desc.subtype.sink_subtype = CORESIGHT_DEV_SUBTYPE_SINK_BUFFER;
 		desc.subtype.link_subtype = CORESIGHT_DEV_SUBTYPE_LINK_FIFO;