Re: [PATCH V5 - RESEND 1/3] coresight: etm: Override TRCIDR3.CCITMIN on errata affected cpus

[Suzuki K Poulose <suzuki.poulose@xxxxxxx>]

On 20/09/2023 07:40, Anshuman Khandual wrote:
> On 9/19/23 16:56, Suzuki K Poulose wrote:
> > Hi Anshuman

> > > +
> > > +static bool etm4_core_reads_wrong_ccitmin(struct etmv4_drvdata *drvdata)
> > > +{
> > > +    /*
> > > +     * Erratum affected cpus will read 256 as the minimum
> > > +     * instruction trace cycle counting threshold whereas
> > > +     * the correct value should be 4 instead. Override the
> > > +     * recorded value for 'drvdata->ccitmin' to workaround
> > > +     * this problem.
> > > +     */
> > > +    return is_midr_in_range_list(read_cpuid_id(), etm_wrong_ccitmin_cpus) &&
> > > +           (drvdata->ccitmin == 256);
> >
> > minor nit: Having looked at this, it feels like, fixing the ccitmin
> > value to 4, could be moved into this function. Otherwise,  we have all
> > the required information about the erratum and the real application of
> > work around is left in the caller, which kind of feels disconnected.
> >
> > So, please could we rename the above function to:
> >
> > static void etm4_fixup_wrong_ccitmin(str..)
> > {
> >    /* Comment as above */
> >     if (....)
> >      drvdata->ccitmin = 4;
> > }
>
> I will fold in the following change for the patch. Please do let me
> know if this reflects your suggestions accurately. Also planning to
> carry Mike's tag after the change.
>
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index 044aed25979b..5b6a878a2ac5 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -1175,7 +1175,7 @@ static struct midr_range etm_wrong_ccitmin_cpus[] = {
>          {},
>   };
>   
> -static bool etm4_core_reads_wrong_ccitmin(struct etmv4_drvdata *drvdata)
> +static void etm4_fixup_wrong_ccitmin(struct etmv4_drvdata *drvdata)
>   {
>          /*
>           * Erratum affected cpus will read 256 as the minimum
> @@ -1184,8 +1184,10 @@ static bool etm4_core_reads_wrong_ccitmin(struct etmv4_drvdata *drvdata)
>           * recorded value for 'drvdata->ccitmin' to workaround
>           * this problem.
>           */
> -       return is_midr_in_range_list(read_cpuid_id(), etm_wrong_ccitmin_cpus) &&
> -              (drvdata->ccitmin == 256);
> +       if (is_midr_in_range_list(read_cpuid_id(), etm_wrong_ccitmin_cpus)) {
> +               if (drvdata->ccitmin == 256)
> +                       drvdata->ccitmin = 4;
> +       }
>   }
>   
>   static void etm4_init_arch_data(void *info)
> @@ -1252,8 +1254,7 @@ static void etm4_init_arch_data(void *info)
>          etmidr3 = etm4x_relaxed_read32(csa, TRCIDR3);
>          /* CCITMIN, bits[11:0] minimum threshold value that can be programmed */
>          drvdata->ccitmin = FIELD_GET(TRCIDR3_CCITMIN_MASK, etmidr3);
> -       if (etm4_core_reads_wrong_ccitmin(drvdata))
> -               drvdata->ccitmin = 4;
> +       etm4_fixup_wrong_ccitmin(drvdata);
>   
>          /* EXLEVEL_S, bits[19:16] Secure state instruction tracing */
>          drvdata->s_ex_level = FIELD_GET(TRCIDR3_EXLEVEL_S_MASK, etmidr3);


LGTM, thanks for addressing it quickly

Suzuki