Re: [PATCH v3 23/26] coresight: etm4x: Detect system instructions support

[Mathieu Poirier]

On Wed, Oct 28, 2020 at 10:09:42PM +0000, Suzuki K Poulose wrote:
> ETM v4.4 onwards adds support for system instruction access
> to the ETM. Detect the support on an ETM and switch to using the
> mode when available.
> 
> Signed-off-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>
> ---
>  .../coresight/coresight-etm4x-core.c          | 39 +++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index 4bc2f15b6332..dc537b5612eb 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -675,6 +675,37 @@ static const struct coresight_ops etm4_cs_ops = {
>  	.source_ops	= &etm4_source_ops,
>  };
>  
> +static inline bool cpu_supports_sysreg_trace(void)
> +{
> +	u64 dfr0 = read_sysreg_s(SYS_ID_AA64DFR0_EL1);
> +
> +	return ((dfr0 >> ID_AA64DFR0_TRACEVER_SHIFT) & 0xfUL) > 0;

I would do:

        return ((dfr0 >> ID_AA64DFR0_TRACEVER_SHIFT) & 0xfUL) == 1;

Because any other value than '1' are reserved.

> +}
> +
> +static bool etm_init_sysreg_access(struct etmv4_drvdata *drvdata,
> +				   struct csdev_access *csa)
> +{
> +	u32 devarch;
> +
> +	if (!cpu_supports_sysreg_trace())
> +		return false;
> +
> +	/*
> +	 * ETMs implementing sysreg access must implement TRCDEVARCH.
> +	 */
> +	devarch = read_etm4x_sysreg_const_offset(TRCDEVARCH);
> +	if ((devarch & ETM_DEVARCH_ID_MASK) != ETM_DEVARCH_ETMv4x_ARCH)
> +		return false;
> +	*csa = (struct csdev_access) {
> +		.io_mem	= false,
> +		.read	= etm4x_sysreg_read,
> +		.write	= etm4x_sysreg_write,
> +	};
> +
> +	drvdata->arch = etm_devarch_to_arch(devarch);
> +	return true;
> +}
> +
>  static bool etm_init_iomem_access(struct etmv4_drvdata *drvdata,
>  				  struct csdev_access *csa)
>  {
> @@ -705,9 +736,17 @@ static bool etm_init_iomem_access(struct etmv4_drvdata *drvdata,
>  static bool etm_init_csdev_access(struct etmv4_drvdata *drvdata,
>  				  struct csdev_access *csa)
>  {
> +	/*
> +	 * Always choose the memory mapped io, if there is
> +	 * a memory map to prevent sysreg access on broken
> +	 * systems.
> +	 */
>  	if (drvdata->base)
>  		return etm_init_iomem_access(drvdata, csa);
>  
> +	if (etm_init_sysreg_access(drvdata, csa))
> +		return true;
> +
>  	return false;

With the above:

Reviewed-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>

>  }
>  
> -- 
> 2.24.1
>