Re: [PATCH] coresight: etm4x: Enable ETE device accessed via MMIO

[Ruidong Tian]

Hi Suzuki,

Now ETM4X driver use MMIO or system instruction depends on this check in 
function etm4_init_csdev_access:

        if (drvdata->base)
                return etm4_init_iomem_access(drvdata, csa);

This check always true if firmware provides a address range in ACPI
table of ETE, and as a result, the ETE device in this case cannot be
successfully probed.

I think OS should be compatible with this situation, no matter firmware
how to organize ETE information in ACPI table. How do you feel about
it?

Thank you

Ruidong Tian
在 2023/10/18 16:28, Suzuki K Poulose 写道:
> On 18/10/2023 08:05, Ruidong Tian wrote:
> > The ETM4X driver now assume that all ETE as CPU system instructions
> > accessed device, in fact the ETE device on some machines also accessed
> > via MMIO.
> >
> > Signed-off-by: Ruidong Tian <tianruidong@xxxxxxxxxxxxxxxxx>
>
> Why are we going backwards to MMIO from system instructions ? Is it 
> because of an "unfriendly" hypervisor preventing access ?
>
> As such, without a sufficiently acceptable explanation, I am reluctant
> to make this change
>
> Suzuki
>
> > ---
> >   drivers/hwtracing/coresight/coresight-etm4x-core.c | 5 +++--
> >   1 file changed, 3 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c 
> > b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > index 285539104bcc..ad298c9cc87e 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > @@ -1103,8 +1103,9 @@ static bool etm4_init_iomem_access(struct 
> > etmv4_drvdata *drvdata,
> >        * with MMIO. But we cannot touch the OSLK until we are
> >        * sure this is an ETM. So rely only on the TRCDEVARCH.
> >        */
> > -    if ((devarch & ETM_DEVARCH_ID_MASK) != ETM_DEVARCH_ETMv4x_ARCH) {
> > -        pr_warn_once("TRCDEVARCH doesn't match ETMv4 architecture\n");
> > +    if ((devarch & ETM_DEVARCH_ID_MASK) != ETM_DEVARCH_ETMv4x_ARCH &&
> > +        (devarch & ETM_DEVARCH_ID_MASK) != ETM_DEVARCH_ETE_ARCH) {
> > +        pr_warn_once("TRCDEVARCH doesn't match ETMv4/ETE 
> > architecture\n");
> >           return false;
> >       }