On 1 May 2018 at 07:13, Rob Herring <[email protected]> wrote: > On Tue, May 01, 2018 at 10:10:40AM +0100, Suzuki K Poulose wrote: >> We are about to add the support for ETR builtin scatter-gather mode >> for dealing with large amount of trace buffers. However, on some of >> the platforms, using the ETR SG mode can lock up the system due to >> the way the ETR is connected to the memory subsystem. >> >> In SG mode, the ETR performs READ from the scatter-gather table to >> fetch the next page and regular WRITE of trace data. If the READ >> operation doesn't complete(due to the memory subsystem issues, >> which we have seen on a couple of platforms) the trace WRITE >> cannot proceed leading to issues. So, we by default do not >> use the SG mode, unless it is known to be safe on the platform. >> We define a DT property for the TMC node to specify whether we >> have a proper SG mode. >> >> Cc: Mathieu Poirier <[email protected]> >> Cc: Mike Leach <[email protected]> >> Cc: Mark Rutland <[email protected]> >> Cc: John Horley <[email protected]> >> Cc: Robert Walker <[email protected]> >> Cc: [email protected] >> Cc: [email protected] >> Cc: Rob Herring <[email protected]> >> Signed-off-by: Suzuki K Poulose <[email protected]> >> --- >> Documentation/devicetree/bindings/arm/coresight.txt | 3 +++ >> drivers/hwtracing/coresight/coresight-tmc.c | 8 +++++++- >> 2 files changed, 10 insertions(+), 1 deletion(-) >> >> diff --git a/Documentation/devicetree/bindings/arm/coresight.txt >> b/Documentation/devicetree/bindings/arm/coresight.txt >> index cdd84d0..7c0c8f0 100644 >> --- a/Documentation/devicetree/bindings/arm/coresight.txt >> +++ b/Documentation/devicetree/bindings/arm/coresight.txt >> @@ -88,6 +88,9 @@ its hardware characteristcs. >> * arm,buffer-size: size of contiguous buffer space for TMC ETR >> (embedded trace router) >> >> + * scatter-gather: boolean. Indicates that the TMC-ETR can safely >> + use the SG mode on this system. >> + > > Needs a vendor prefix. >
Thinking further on this, do we need to make it device specific as well - something like "arm,etr-scatter-gather"? That way we don't have to redefine "scatter-gather" for other ARM devices if they happen to need the same property but for different reasons. >> * Optional property for CATU : >> * interrupts : Exactly one SPI may be listed for reporting the address >> error
