Re: [PATCH] coresight: tmc: Enable SG capability on ACPI based SoC-400 TMC ETR devices

[James Clark <james.clark@arm.com>]

On 04/04/2024 08:29, Anshuman Khandual wrote:
> This detects and enables the scatter gather capability (SG) on ACPI based
> Soc-400 TMC ETR devices via a new property called 'arm-armhc97c-sg-enable'.
> The updated ACPI spec can be found below, which contains this new property.
> 
> https://developer.arm.com/documentation/den0067/latest/
> 
> This preserves current handling for the property 'arm,scatter-gather' both
> on ACPI and DT based platforms i.e the presence of the property is checked
> instead of the value.
> 
> Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
> Cc: Mike Leach <mike.leach@linaro.org>
> Cc: James Clark <james.clark@arm.com>
> 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>
> ---
>  .../hwtracing/coresight/coresight-tmc-core.c  | 28 ++++++++++++++++++-
>  1 file changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-core.c b/drivers/hwtracing/coresight/coresight-tmc-core.c
> index 72005b0c633e..2b277499b59a 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-core.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-core.c
> @@ -4,6 +4,7 @@
>   * Description: CoreSight Trace Memory Controller driver
>   */
>  
> +#include <linux/acpi.h>
>  #include <linux/kernel.h>
>  #include <linux/init.h>
>  #include <linux/types.h>
> @@ -360,7 +361,32 @@ static const struct attribute_group *coresight_etr_groups[] = {
>  
>  static inline bool tmc_etr_can_use_sg(struct device *dev)
>  {
> -	return fwnode_property_present(dev->fwnode, "arm,scatter-gather");
> +	int ret;
> +	u8 val_u8;
> +
> +	/*
> +	 * Presence of the property 'arm,scatter-gather' is checked
> +	 * on the platform for the feature support, rather than its
> +	 * value.
> +	 */
> +	if (is_of_node(dev->fwnode)) {
> +		return fwnode_property_present(dev->fwnode, "arm,scatter-gather");
> +	} else if (is_acpi_device_node(dev->fwnode)) {
> +		/*
> +		 * TMC_DEVID_NOSCAT test in tmc_etr_setup_caps(), has already ensured
> +		 * this property is only checked for Coresight SoC 400 TMC configured
> +		 * as ETR.
> +		 */
> +		ret = fwnode_property_read_u8(dev->fwnode, "arm-armhc97c-sg-enable", &val_u8);
> +		if (!ret)
> +			return !!val_u8;
> +
> +		if (fwnode_property_present(dev->fwnode, "arm,scatter-gather")) {
> +			pr_warn_once("Deprecated ACPI property - arm,scatter-gather\n");
> +			return true;
> +		}
> +	}
> +	return false;
>  }
>  
>  static inline bool tmc_etr_has_non_secure_access(struct tmc_drvdata *drvdata)


Reviewed-by: James Clark <james.clark@arm.com>