Re: [PATCH 3/7] coresight: Only check bottom two claim bits

[Leo Yan <leo.yan@arm.com>]

On Tue, Feb 11, 2025 at 10:39:39AM +0000, James Clark wrote:
> 
> The use of the whole register and == could break the claim mechanism if
> any of the other bits are used in the future. The referenced doc "PSCI -
> ARM DEN 0022D" also says to only read and clear the bottom two bits.
> 
> Use FIELD_GET() to extract only the relevant part.
> 
> Signed-off-by: James Clark <james.clark@linaro.org>

I checked the latest PSCI spec DEN0022F.b, which has no change for
for only using lowest two bits in claim register.

Reviewed-by: Leo Yan <leo.yan@arm.com>


> ---
>  drivers/hwtracing/coresight/coresight-core.c | 3 ++-
>  drivers/hwtracing/coresight/coresight-priv.h | 1 +
>  2 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-core.c b/drivers/hwtracing/coresight/coresight-core.c
> index a669872b4118..7b53165c93af 100644
> --- a/drivers/hwtracing/coresight/coresight-core.c
> +++ b/drivers/hwtracing/coresight/coresight-core.c
> @@ -129,7 +129,8 @@ coresight_find_out_connection(struct coresight_device *csdev,
> 
>  static inline u32 coresight_read_claim_tags(struct csdev_access *csa)
>  {
> -       return csdev_access_relaxed_read32(csa, CORESIGHT_CLAIMCLR);
> +       return FIELD_GET(CORESIGHT_CLAIM_MASK,
> +                        csdev_access_relaxed_read32(csa, CORESIGHT_CLAIMCLR));
>  }
> 
>  static inline bool coresight_is_claimed_self_hosted(struct csdev_access *csa)
> diff --git a/drivers/hwtracing/coresight/coresight-priv.h b/drivers/hwtracing/coresight/coresight-priv.h
> index 05f891ca6b5c..cc7ff1e36ef4 100644
> --- a/drivers/hwtracing/coresight/coresight-priv.h
> +++ b/drivers/hwtracing/coresight/coresight-priv.h
> @@ -35,6 +35,7 @@ extern const struct device_type coresight_dev_type[];
>   * Coresight device CLAIM protocol.
>   * See PSCI - ARM DEN 0022D, Section: 6.8.1 Debug and Trace save and restore.
>   */
> +#define CORESIGHT_CLAIM_MASK           GENMASK(1, 0)
>  #define CORESIGHT_CLAIM_SELF_HOSTED    BIT(1)
> 
>  #define TIMEOUT_US             100
> --
> 2.34.1
> 
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