[PATCH 19/19] dts: bindings: coresight: ETMv4.4 system register access only units

[Mike Leach]

Hi suzuki,

On Thu, 24 Sep 2020 at 10:43, Suzuki K Poulose <suzuki.poulose at arm.com> wrote:
>
> On 09/18/2020 04:35 PM, Mike Leach wrote:
> > On Fri, 11 Sep 2020 at 09:41, Suzuki K Poulose <suzuki.poulose at arm.com> wrote:
> >>
> >> Document the bindings for ETMv4.4 and later with only system register
> >> access.
> >>
> >> Cc: devicetree at vger.kernel.org
> >> Cc: Mathieu Poirier <mathieu.poirier at linaro.org>
> >> Cc: Mike Leach <mike.leach at linaro.org>
> >> Reviewed-by: Rob Herring <robh at kernel.org>
> >> Signed-off-by: Suzuki K Poulose <suzuki.poulose at arm.com>
> >> ---
> >>   Documentation/devicetree/bindings/arm/coresight.txt | 6 +++++-
> >>   1 file changed, 5 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/Documentation/devicetree/bindings/arm/coresight.txt b/Documentation/devicetree/bindings/arm/coresight.txt
> >> index d711676b4a51..cfe47bdda728 100644
> >> --- a/Documentation/devicetree/bindings/arm/coresight.txt
> >> +++ b/Documentation/devicetree/bindings/arm/coresight.txt
> >> @@ -34,9 +34,13 @@ its hardware characteristcs.
> >>                                          Program Flow Trace Macrocell:
> >>                          "arm,coresight-etm3x", "arm,primecell";
> >>
> >> -               - Embedded Trace Macrocell (version 4.x):
> >> +               - Embedded Trace Macrocell (version 4.x), with memory mapped access.
> >>                          "arm,coresight-etm4x", "arm,primecell";
> >>
> >> +               - Embedded Trace Macrocell (version 4.4 and later) with system
> >> +                 register access only.
> >> +                       "arm,coresight-etm-v4.4";
> >
> > Any version of ETM can implement register access - including those pre
> > ETM 4.4. Perhaps the new name should simply reflect sys reg access
> > rather than a version.
> >
>
> You're right. I got it confused with the v8.4 SelfHosted Extensions, which
> mandates the sysreg access and makes the mem I/O obsolete. How about :
>
>         "arm,coresight-etm4x-sysreg" ?
>
>
Seems reasonable.
Perhaps ensure that the accompanying comment mentions that this is
aarch64 access (to cover the unlikely event that some outlier
implementation does come along with v8 aarch32 + ETMv4 + sysreg
access!)

> > Given that the two compatibility strings should be mutually exclusive
> > for a given device, should the bindings doc (or at least the etm4x
> > component part) be re-written into the .yaml format so that this can
> > be enforced?
>
> I will take a look, haven't played with the yaml.
>

I used it to describe the CTI bindings as these were brand new.
Reasonably straight forwards - there are plenty of examples and the
checking tools are pretty good.

Regards

Mike


> Thanks for the review !
>
> Suzuki



-- 
Mike Leach
Principal Engineer, ARM Ltd.
Manchester Design Centre. UK