RE: [EXT] Re: [PATCH 1/7] dt-bindings: arm: coresight-tmc: Add "memory-region" property

[Linu Cherian]

Hi Mike,

> -----Original Message-----
> From: Linu Cherian
> Sent: Saturday, October 14, 2023 5:07 PM
> To: Mike Leach <mike.leach@xxxxxxxxxx>
> Cc: suzuki.poulose@xxxxxxx; james.clark@xxxxxxx; leo.yan@xxxxxxxxxx;
> linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; coresight@xxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; robh+dt@xxxxxxxxxx;
> krzysztof.kozlowski+dt@xxxxxxxxxx; conor+dt@xxxxxxxxxx;
> devicetree@xxxxxxxxxxxxxxx; Sunil Kovvuri Goutham
> <sgoutham@xxxxxxxxxxx>; George Cherian <gcherian@xxxxxxxxxxx>
> Subject: RE: [EXT] Re: [PATCH 1/7] dt-bindings: arm: coresight-tmc: Add
> "memory-region" property
> 
> Hi Mike,
> 
> > -----Original Message-----
> > From: Mike Leach <mike.leach@xxxxxxxxxx>
> > Sent: Friday, October 6, 2023 4:33 PM
> > To: Linu Cherian <lcherian@xxxxxxxxxxx>
> > Cc: suzuki.poulose@xxxxxxx; james.clark@xxxxxxx; leo.yan@xxxxxxxxxx;
> > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; coresight@xxxxxxxxxxxxxxxx;
> > linux- kernel@xxxxxxxxxxxxxxx; robh+dt@xxxxxxxxxx;
> > krzysztof.kozlowski+dt@xxxxxxxxxx; conor+dt@xxxxxxxxxx;
> > devicetree@xxxxxxxxxxxxxxx; Sunil Kovvuri Goutham
> > <sgoutham@xxxxxxxxxxx>; George Cherian <gcherian@xxxxxxxxxxx>
> > Subject: [EXT] Re: [PATCH 1/7] dt-bindings: arm: coresight-tmc: Add
> > "memory-region" property
> >
> > External Email
> >
> > ----------------------------------------------------------------------
> > Hi Linu
> >
> > On Fri, 29 Sept 2023 at 14:38, Linu Cherian <lcherian@xxxxxxxxxxx> wrote:
> > >
> > > memory-region 0: Reserved trace buffer memory
> > >
> > >   TMC ETR: When available, use this reserved memory region for
> > >   trace data capture. Same region is used for trace data
> > >   retention after a panic or watchdog reset.
> > >
> > >   TMC ETF: When available, use this reserved memory region for
> > >   trace data retention synced from internal SRAM after a panic or
> > >   watchdog reset.
> > >
> > > memory-region 1: Reserved meta data memory
> > >
> > >   TMC ETR, ETF: When available, use this memory for register
> > >   snapshot retention synced from hardware registers after a panic
> > >   or watchdog reset.
> > >
> > > Signed-off-by: Linu Cherian <lcherian@xxxxxxxxxxx>
> > > ---
> > >  .../bindings/arm/arm,coresight-tmc.yaml       | 19
> +++++++++++++++++++
> > >  1 file changed, 19 insertions(+)
> > >
> > > diff --git
> > > a/Documentation/devicetree/bindings/arm/arm,coresight-tmc.yaml
> > > b/Documentation/devicetree/bindings/arm/arm,coresight-tmc.yaml
> > > index cb8dceaca70e..45ca4d02d73e 100644
> > > --- a/Documentation/devicetree/bindings/arm/arm,coresight-tmc.yaml
> > > +++ b/Documentation/devicetree/bindings/arm/arm,coresight-tmc.yaml
> > > @@ -101,6 +101,22 @@ properties:
> > >            and ETF configurations.
> > >          $ref: /schemas/graph.yaml#/properties/port
> > >
> > > +  memory-region:
> > > +    items:
> > > +      - description: Reserved trace buffer memory for ETR and ETF sinks.
> > > +          For ETR, this reserved memory region is used for trace data
> capture.
> > > +          Same region is used for trace data retention as well after a panic
> > > +          or watchdog reset.
> > > +          For ETF, this reserved memory region is used for retention of trace
> > > +          data synced from internal SRAM after a panic or watchdog reset.
> > > +
> >
> > Is there a valid use case for ETR where we use these areas when there
> > is not a panic/reset situation?
> >
> 
> Currently its meant to be used only for the panic/reset situations and gets
> enabled only with a special buffer mode.
> 
> > Either way - the description should perhaps mention that these areas
> > are only used if specifically selected by the driver - the default
> > memory usage models for ETR / perf are otherwise unaltered.
> 
> Ack.
> 
> >
> > > +      - description: Reserved meta data memory. Used for ETR and ETF
> sinks.
> > > +
> > > +  memory-region-names:
> > > +    items:
> > > +      - const: trace-mem
> > > +      - const: metadata-mem
> > > +
> >
> > Is there a constraint required here? If we are using the memory area
> > for trace in a panic situation, then we must have the meta data memory
> > area defined?
> > Perhaps a set of names such as "etr-trace-mem", "panic-trace-mem" ,
> > "panic-metadata-mem", were the first is for general ETR trace in
> > non-panic situation and then constrain the "panic-" areas to appear
> together.
> > The "etr-trace-mem", "panic-trace-mem" could easily point to the same
> > area.
> >
> As noted above, we do not have other generic use case for these reserved
> regions now.
> Hence two regions/names, panic-trace-mem and panic-metadata-mem with
> constraints kept as
>  minItems: 2 and maxItems: 2 would suffice ?

Looking this further, realized that by default minItems and maxItems are 2 in this case.
IIUC, nothing additional required to enforce this constraint.

Also tested this, with the below dts change with just one memory-region,

diff --git a/arch/arm64/boot/dts/arm/juno-cs-r1r2.dtsi b/arch/arm64/boot/dts/arm/juno-cs-r1r2.dtsi
index 09d2b692e9e1..03ff6b2f7269 100644
--- a/arch/arm64/boot/dts/arm/juno-cs-r1r2.dtsi
+++ b/arch/arm64/boot/dts/arm/juno-cs-r1r2.dtsi
@@ -30,6 +30,9 @@ etf_sys1: etf@20140000 { /* etf1 */
                clocks = <&soc_smc50mhz>;
                clock-names = "apb_pclk";
                power-domains = <&scpi_devpd 0>;
+               memory-region = <&etf1_trace>;
+               memory-region-names = "tracedata";
+
                in-ports {


Validation of DTS files using below command identified this.
# make CHECK_DTBS=y ARCH=arm64  arm/juno-r2-scmi.dtb 

     from schema $id: http://devicetree.org/schemas/thermal/thermal-zones.yaml#
/home/lcherian/scode/mainline/linux/arch/arm64/boot/dts/arm/juno-r2-scmi.dtb: etf@20140000: memory-region: [[72]] is too short
        from schema $id: http://devicetree.org/schemas/arm/arm,coresight-tmc.yaml#
/home/lcherian/scode/mainline/linux/arch/arm64/boot/dts/arm/juno-r2-scmi.dtb: etf@20140000: memory-region-names: ['tracedata'] is too short
        from schema $id: http://devicetree.org/schemas/arm/arm,coresight-tmc.yaml#
/home/lcherian/scode/mainline/linux/arch/arm64/boot/dts/arm/juno-r2-scmi.dtb: etf@20140000: Unevaluated properties are not allowed ('memory-region', 'memory-region-names' were unexp
ected)