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

[Ruidong Tian]

Hi Suzuki

You are right, I review armv9 Spec again, and find that ETE only
support system instructions access.  This patch is meaningless and
need to drop it.

Ruidong

在 2023/10/18 17:36, Suzuki K Poulose 写道:
> Hi
>
> On 18/10/2023 10:30, Ruidong Tian wrote:
> > 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?
>
> My question is not about "What the patch does". But, why can't we use
> system instructions on your system, when ETE was designed to be used
> with that in the first place and get rid of the MMIO.
>
> Suzuki
>
> > 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;
> > > >       }