linux-kernel - Re: [PATCH 08/20] coresight: dts: Cleanup device tree graph bindings

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Message-ID: <0a213578-c7d7-0ed3-ffc1-afc97d8d1516@arm.com>
Date:   Mon, 11 Jun 2018 17:55:26 +0100
From:   Suzuki K Poulose <Suzuki.Poulose@....com>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Rob Herring <robh@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        Sudeep Holla <sudeep.holla@....com>, arm@...nel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Matt Sealey <matt.sealey@....com>,
        John Horley <john.horley@....com>,
        Charles Garcia-Tobin <charles.garcia-tobin@....com>,
        coresight@...ts.linaro.org, devicetree@...r.kernel.org,
        Mike Leach <mike.leach@...aro.org>
Subject: Re: [PATCH 08/20] coresight: dts: Cleanup device tree graph bindings

On 11/06/18 17:52, Mathieu Poirier wrote:
> On 11 June 2018 at 03:22, Suzuki K Poulose <Suzuki.Poulose@....com> wrote:
>> On 08/06/18 22:22, Mathieu Poirier wrote:
>>>
>>> On Tue, Jun 05, 2018 at 10:43:19PM +0100, Suzuki K Poulose wrote:
>>>>
>>>> The coresight drivers relied on default bindings for graph
>>>> in DT, while reusing the "reg" field of the "ports" to indicate
>>>> the actual hardware port number for the connections. However,
>>>> with the rules getting stricter w.r.t to the address mismatch
>>>> with the label, it is no longer possible to use the port address
>>>> field for the hardware port number. Hence, we add an explicit
>>>> property to denote the hardware port number, "coresight,hwid"
>>>> which must be specified for each "endpoint".
>>>>
>>>> Cc: Mathieu Poirier <mathieu.poirier@...aro.org>
>>>> Cc: Sudeep Holla <sudeep.holla@....com>
>>>> Cc: Rob Herring <robh@...nel.org>
>>>> Signed-off-by: Suzuki K Poulose <suzuki.poulose@....com>
>>>> ---
>>>>    .../devicetree/bindings/arm/coresight.txt          | 29 ++++++++++---
>>>>    drivers/hwtracing/coresight/of_coresight.c         | 49
>>>> +++++++++++++++++-----
>>>>    2 files changed, 62 insertions(+), 16 deletions(-)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/arm/coresight.txt
>>>> b/Documentation/devicetree/bindings/arm/coresight.txt
>>>> index ed6b555..bf75ab3 100644
>>>> --- a/Documentation/devicetree/bindings/arm/coresight.txt
>>>> +++ b/Documentation/devicetree/bindings/arm/coresight.txt
>>>> @@ -108,8 +108,13 @@ following properties to uniquely identify the
>>>> connection details.
>>>>          "slave-mode"
>>
>>
>>
>>>>          };
>>>
>>>
>>> For the binding part:
>>> Reviewed-by: Mathieu Poirier <mathieu.poirier@...aro.org>

...

>>>> @@ -140,9 +166,6 @@ static int of_coresight_parse_endpoint(struct
>>>> device_node *ep,
>>>>                  rparent = of_graph_get_port_parent(rep);
>>>>                  if (!rparent)
>>>>                          break;
>>>> -               if (of_graph_parse_endpoint(rep, &rendpoint))
>>>> -                       break;
>>>> -
>>>>                  /* If the remote device is not available, defer probing
>>>> */
>>>>                  rdev = of_coresight_get_endpoint_device(rparent);
>>>>                  if (!rdev) {
>>>> @@ -150,9 +173,15 @@ static int of_coresight_parse_endpoint(struct
>>>> device_node *ep,
>>>>                          break;
>>>>                  }
>>>>    -             conn->outport = endpoint.port;
>>>> +               child_port = of_coresight_endpoint_get_port_id(rdev,
>>>> rep);
>>>> +               if (child_port < 0) {
>>>> +                       ret = 0;
>>>
>>>
>>> Why returning '0' on an error condition?  Same for 'local_port' above.
>>>
>>
>> If we are unable to parse a port, we can simply ignore the port and
>> continue, which
>> is what we have today with the existing code. I didn't change it and still
>> think
>> it is the best effort thing. We could spit a warning for such cases, if
>> really needed.
>> Also, the parsing code almost never fails at the moment. If it fails to find
>> "reg" field,
>> it is assumed to be '0'. Either way ignoring it seems harmless. That said I
>> am open
>> to suggestions.
> 
> Looking at the original code I remember not mandating enpoints to be
> valid for debugging purposes.  That certainly helps when building up a
> device tree file but also has the side effect of silently overlooking
> specification problems.  Fortunately the revamping you did on that
> part of the code makes it very easy to change that, something I think
> we should take advantage of (it can only lead to positive scenarios
> where defective specifications get pointed out).
> 
> That being said and because the original behaviour is just as
> permissive, you can leave as is.

Thanks. So can I assume the Reviewed-by applies for the code now ?

Suzuki