We are about to add the support for ETR builtin scatter-gather mode for dealing with large amount of trace buffers. However, on some of the platforms, using the ETR SG mode can lock up the system due to the way the ETR is connected to the memory subsystem.
In SG mode, the ETR performs READ from the scatter-gather table to fetch the next page and regular WRITE of trace data. If the READ operation doesn't complete(due to the memory subsystem issues, which we have seen on a couple of platforms) the trace WRITE cannot proceed leading to issues. So, we by default do not use the SG mode, unless it is known to be safe on the platform. We define a DT property for the TMC node to specify whether we have a proper SG mode.
Cc: Mathieu Poirier mathieu.poirier@linaro.org Cc: Mike Leach mike.leach@linaro.org Cc: Mark Rutland mark.rutland@arm.com Cc: John Horley john.horley@arm.com Cc: Robert Walker robert.walker@arm.com Cc: devicetree@vger.kernel.org Cc: frowand.list@gmail.com Cc: Rob Herring robh@kernel.org Signed-off-by: Suzuki K Poulose suzuki.poulose@arm.com --- Documentation/devicetree/bindings/arm/coresight.txt | 2 ++ drivers/hwtracing/coresight/coresight-tmc.c | 9 ++++++++- 2 files changed, 10 insertions(+), 1 deletion(-)
diff --git a/Documentation/devicetree/bindings/arm/coresight.txt b/Documentation/devicetree/bindings/arm/coresight.txt index 15ac8e8..603d3c6 100644 --- a/Documentation/devicetree/bindings/arm/coresight.txt +++ b/Documentation/devicetree/bindings/arm/coresight.txt @@ -86,6 +86,8 @@ its hardware characteristcs. * arm,buffer-size: size of contiguous buffer space for TMC ETR (embedded trace router)
+ * arm,scatter-gather: boolean. Indicates that the TMC-ETR can safely + use the SG mode on this system.
Example:
diff --git a/drivers/hwtracing/coresight/coresight-tmc.c b/drivers/hwtracing/coresight/coresight-tmc.c index 93c5bfc..7d8331d 100644 --- a/drivers/hwtracing/coresight/coresight-tmc.c +++ b/drivers/hwtracing/coresight/coresight-tmc.c @@ -20,6 +20,7 @@ #include <linux/err.h> #include <linux/fs.h> #include <linux/miscdevice.h> +#include <linux/property.h> #include <linux/uaccess.h> #include <linux/slab.h> #include <linux/dma-mapping.h> @@ -304,6 +305,12 @@ const struct attribute_group *coresight_tmc_groups[] = { NULL, };
+static inline bool tmc_etr_can_use_sg(struct tmc_drvdata *drvdata) +{ + return fwnode_property_present(drvdata->dev->fwnode, + "arm,scatter-gather"); +} + /* Detect and initialise the capabilities of a TMC ETR */ static int tmc_etr_setup_caps(struct tmc_drvdata *drvdata, u32 devid, void *dev_caps) @@ -313,7 +320,7 @@ static int tmc_etr_setup_caps(struct tmc_drvdata *drvdata, /* Set the unadvertised capabilities */ tmc_etr_init_caps(drvdata, (u32)(unsigned long)dev_caps);
- if (!(devid & TMC_DEVID_NOSCAT)) + if (!(devid & TMC_DEVID_NOSCAT) && tmc_etr_can_use_sg(drvdata)) tmc_etr_set_cap(drvdata, TMC_ETR_SG);
/* Check if the AXI address width is available */