linux-kernel - Re: [PATCH v7 8/8] interconnect: Allow endpoints translation via DT

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Message-ID: <df517d56-a181-b72b-2fb4-cb58bb817a99@linaro.org>
Date:   Thu, 9 Aug 2018 17:17:37 +0300
From:   Georgi Djakov <georgi.djakov@...aro.org>
To:     skannan@...eaurora.org
Cc:     linux-pm@...r.kernel.org, gregkh@...uxfoundation.org,
        rjw@...ysocki.net, robh+dt@...nel.org, mturquette@...libre.com,
        khilman@...libre.com, vincent.guittot@...aro.org,
        bjorn.andersson@...aro.org, amit.kucheria@...aro.org,
        seansw@....qualcomm.com, daidavid1@...eaurora.org,
        evgreen@...omium.org, mark.rutland@....com,
        lorenzo.pieralisi@....com, abailon@...libre.com, arnd@...db.de,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v7 8/8] interconnect: Allow endpoints translation via DT

Hi Saravana,

On 08/02/2018 10:12 PM, skannan@...eaurora.org wrote:
> On 2018-08-02 05:07, Georgi Djakov wrote:
>> Hi Saravana,
>>
>> On 08/02/2018 01:57 AM, skannan@...eaurora.org wrote:
>>> On 2018-07-31 09:13, Georgi Djakov wrote:
>>>> Currently we support only platform data for specifying the interconnect
>>>> endpoints. As now the endpoints are hard-coded into the consumer driver
>>>> this may lead to complications when a single driver is used by multiple
>>>> SoCs, which may have different interconnect topology.
>>>> To avoid cluttering the consumer drivers, introduce a translation
>>>> function
>>>> to help us get the board specific interconnect data from device-tree.
>>>>
>>>> Signed-off-by: Georgi Djakov <georgi.djakov@...aro.org>
>>>> ---
>>>>  drivers/interconnect/core.c  | 62 ++++++++++++++++++++++++++++++++++++
>>>>  include/linux/interconnect.h |  7 ++++
>>>>  2 files changed, 69 insertions(+)
>>>>
>>>> diff --git a/drivers/interconnect/core.c b/drivers/interconnect/core.c
>>>> index 9fef180cf77e..d1b6adff0a3d 100644
>>>> --- a/drivers/interconnect/core.c
>>>> +++ b/drivers/interconnect/core.c
>> [..]
>>>> --- a/include/linux/interconnect.h
>>>> +++ b/include/linux/interconnect.h
>>>> @@ -17,6 +17,7 @@ struct device;
>>>>
>>>>  struct icc_path *icc_get(struct device *dev, const int src_id,
>>>>               const int dst_id);
>>>> +struct icc_path *of_icc_get(struct device *dev, const char *name);
>>>>  void icc_put(struct icc_path *path);
>>>>  int icc_set(struct icc_path *path, u32 avg_bw, u32 peak_bw);
>>>>
>>>> @@ -28,6 +29,12 @@ static inline struct icc_path *icc_get(struct
>>>> device *dev, const int src_id,
>>>>      return NULL;
>>>>  }
>>>>
>>>> +static inline struct icc_path *of_icc_get(struct device *dev,
>>>> +                      const char *name)
>>>> +{
>>>> +    return NULL;
>>>> +}
>>>> +
>>>
>>> Might want to return PTR(-ENODEV) or some error code so that client
>>> doesn't have to do NULL check AND an error check?
>>>
>>> -Saravana
>>
>> NULL is returned when CONFIG_INTERCONNECT=n. Configuration of
>> interconnects by consumer drivers could be optional and that's why null
>> is returned instead of an error. The consumer drivers decide how to
>> proceed in this case and if there is a hard requirement for interconnect
>> support, then i would suggest to express it as a dependency in Kconfig.
> 
> Ehh... you could make the same argument with an error. If it's not
> mandatory for functioning, they can ignore a specific error and
> continue? At a minimum, these stub functions returning NULL doesn't
> match with the documentation that says these APIs will only ever return
> ERR_PTR().
> 
> -Saravana

Here i am trying to align with other frameworks, which provide some
resources to consumers. The regulator/clock/reset frameworks return
NULL, so i prefer to do the same here. Drivers are free to handle NULL
specifically, but they don't have to. This NULL may also mean that
interconnects have been already configured by bootloader or firmware.
Of course i accept the comment to update the documentation to mention this.

Thanks,
Georgi