On Tue, May 01, 2018 at 10:10:42AM +0100, Suzuki K Poulose wrote:
> The Coresight TMC-ETR SG mode could be unsafe on a platform where
> the ETR is not properly connected to account for READ operations.
> We use a DT node property to indicate if the system is safe.
> This patch also provides a command line parameter to "force"
> the use of SG mode to override the firmware information.
>
> Cc: Mathieu Poirier <mathieu.poir...@linaro.org>
> Cc: Mike Leach <mike.le...@linaro.org>
> Signed-off-by: Suzuki K Poulose <suzuki.poul...@arm.com>
> ---
> Hi
>
> This is more of a debug patch for people who may want to
> test their platform without too much of hacking. I am not
> too keen on pushing this patch in.
I am not either nor do I personally need it to test this feature. We can leave
it in for now (and subsequent version) if you need it but we agree that I won't
queue it to my tree when the time comes.
> ---
> Documentation/admin-guide/kernel-parameters.txt | 8 ++++++++
> drivers/hwtracing/coresight/coresight-tmc.c | 7 ++++++-
> 2 files changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> index 11fc28e..03b51c3 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -675,6 +675,14 @@
> Enable/disable the CPU sampling based debugging.
> 0: default value, disable debugging
> 1: enable debugging at boot time
> + coresight_tmc.etr_force_sg
> + [ARM, ARM64]
> + Format: <bool>
> + Force using the TMC ETR builtin scatter-gather mode
> + even when it may be unsafe to use.
> + Default : 0, do not force using the builtin SG mode.
> + 1, Allow using the SG, ignoring the firmware
> + provided information.
>
> cpuidle.off=1 [CPU_IDLE]
> disable the cpuidle sub-system
> diff --git a/drivers/hwtracing/coresight/coresight-tmc.c
> b/drivers/hwtracing/coresight/coresight-tmc.c
> index e38379c..c7bc681 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/module.h>
> #include <linux/property.h>
> #include <linux/uaccess.h>
> #include <linux/slab.h>
> @@ -33,6 +34,8 @@
> #include "coresight-priv.h"
> #include "coresight-tmc.h"
>
> +static bool etr_force_sg;
> +
> void tmc_wait_for_tmcready(struct tmc_drvdata *drvdata)
> {
> /* Ensure formatter, unformatter and hardware fifo are empty */
> @@ -307,7 +310,8 @@ const struct attribute_group *coresight_tmc_groups[] = {
>
> static inline bool tmc_etr_can_use_sg(struct tmc_drvdata *drvdata)
> {
> - return fwnode_property_present(drvdata->dev->fwnode, "scatter-gather");
> + return etr_force_sg ||
> + fwnode_property_present(drvdata->dev->fwnode, "scatter-gather");
> }
>
> /* Detect and initialise the capabilities of a TMC ETR */
> @@ -482,3 +486,4 @@ static struct amba_driver tmc_driver = {
> .id_table = tmc_ids,
> };
> builtin_amba_driver(tmc_driver);
> +module_param(etr_force_sg, bool, 0);
> --
> 2.7.4
>
