On Fri, Jun 01, 2018 at 02:15:59PM +0100, Suzuki K Poulose wrote:
> Coresight uses DT graph bindings to describe the connections of the
> components. However we have some undocumented usage of the bindings
> to describe some of the properties of the connections.
>
> The coresight driver needs to know the hardware ports invovled
> in the connection and the direction of data flow to effectively
> manage the trace sessions. So far we have relied on the "port"
> address (as described by the generic graph bindings) to represent
> the hardware port of the component for a connection.
>
> The hardware uses separate numbering scheme for input and output
> ports, which implies, we could have two different (input and output)
> ports with the same port number. This could create problems in the
> graph bindings where the label of the port wouldn't match the address.
>
> e.g, with the existing bindings we get :
>
> port@0{ // Output port 0
> reg = <0>;
> ...
> };
>
> port@1{
> reg = <0>; // Input port 0
> endpoint {
> slave-mode;
> ...
> };
> };
>
> With the new enforcement in the DT rules, mismatches in label and address
> are not allowed (as see in the case for port@1). So, we need a new mechanism
> to describe the hardware port number reliably.
>
> Also, we relied on an undocumented "slave-mode" property (see the above
> example) to indicate if the port is an input port. Let us formalise and
> switch to a new property to describe the direction of data flow.
>
> There were three options considered for the hardware port number scheme:
>
> 1) Use natural ordering in the DT to infer the hardware port number.
> i.e, Mandate that the all ports are listed in the DT and in the ascending
> order for each class (input and output respectively).
> Pros :
> - We don't need new properties and if the existing DTS list them in
> order (which most of them do), they work out of the box.
> Cons :
> - We must list all the ports even if the system cannot/shouldn't use
> it.
> - It is prone to human errors (if the order is not kept).
>
> 2) Use an explicit property to list both the direction and the hw port
> number and direction. Define "coresight,hwid" as 2 member array of u32,
> where the members are port number and the direction respectively.
> e.g
>
> port@0{
> reg = <0>;
> endpoint {
> coresight,hwid = <0 1>; // Port # 0, Output
> }
> };
>
> port@1{
> reg = <1>;
> endpoint {
> coresight,hwid = <0 0>; // Port # 0, Input
> };
> };
>
> Pros:
> - The bindings are formal but not so reader friendly and could
> potentially
> lead to human errors.
> Cons:
> - Backward compatiblity is lost.
> 3) Use explicit properties (implemented in the series) for the hardware
> port id and direction. We define a new property "coresight,hwid" for
> each endpoint in coresight devices to specify the hardware port number
> explicitly. Also use a separate property "direction" to specify the
> direction of the data flow.
>
> e.g,
>
> port@0{
> reg = <0>;
> endpoint {
> direction = <1>; // Output
> coresight,hwid = <0>; // Port # 0
> }
> };
>
> port@1{
> reg = <1>;
> endpoint {
> direction = <0>; // Input
> coresight,hwid = <0>; // Port # 0
> };
> };
>
> Pros:
> - The bindings are formal and reader friendly, and less prone to
> errors.
> Cons:
> - Backward compatibility is lost.
>
>
> This series achieves implements Option (3) listed above while still retaining
> the backward compatibility. The driver now issues a warning (once) when it
> encounters the old bindings.
> It also cleans up the platform parsing code to reduce the memory usage by
> reusing the platform description. The series also includes the
> changes for Juno platform as an example. If there are no objections
> to the approach, I could post the series, converting all the
> in-kernel DTS to the new binding.
>
> Suzuki K Poulose (8):
> dts: binding: coresight: Document graph bindings
> coresight: Fix remote endpoint parsing
> coresight: Cleanup platform description data
> coresight: platform: Cleanup coresight connection handling
> coresight: Handle errors in finding input/output ports
> dts: coresight: Clean up the device tree graph bindings
> dts: coresight: Define new bindings for direction of data flow
> dts: juno: Update coresight bindings for hw port
>
> .../devicetree/bindings/arm/coresight.txt | 52 ++++++++--
> arch/arm64/boot/dts/arm/juno-base.dtsi | 82 +++++++++++----
> arch/arm64/boot/dts/arm/juno.dts | 5 +-
> drivers/hwtracing/coresight/coresight.c | 28 ++----
> drivers/hwtracing/coresight/of_coresight.c | 111
> ++++++++++++---------
> include/linux/coresight.h | 11 +-
> 6 files changed, 181 insertions(+), 108 deletions(-)
Aside from the comments I've already posted I'm pretty much good with this set.
Please rebase the next revision on my "next" branch and run checkpatch.pl on the
set. Patch 6/8 and 7/8 are generating warnings.
Thanks,
Mathieu
>
> --
> 2.7.4
>
