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

Mathieu Poirier
2020-11-09T20:22:09Z

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@arm.com>
> ---
> .../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@linaro.org>

> }
>
> --
> 2.24.1
>