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

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Message-ID: <CANLsYkyuLVkRWtnVCej2ovDx9RJiA_hADy1XVD+tStFmq0fNrQ@mail.gmail.com>
Date:   Mon, 11 Jun 2018 15:51:11 -0600
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>
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 June 2018 at 10:55, Suzuki K Poulose <Suzuki.Poulose@....com> wrote:
> 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 ?

Yes

>
> Suzuki