linux-kernel - Re: [PATCH] usb: typec: tcpm: Export partner Source Capabilities

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Message-ID: <85ea1e87-eaaa-1540-f693-5601bcafddf6@roeck-us.net>
Date:   Thu, 14 Feb 2019 06:31:18 -0800
From:   Guenter Roeck <linux@...ck-us.net>
To:     Adam Thomson <Adam.Thomson.Opensource@...semi.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Kyle Tso <kyletso@...gle.com>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Badhri Jagan Sridharan <badhri@...gle.com>,
        "linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: typec: tcpm: Export partner Source Capabilities

On 2/14/19 6:17 AM, Adam Thomson wrote:
> On 12 February 2019 16:20, Guenter Roeck wrote:
> 
>> On 2/12/19 2:54 AM, Greg KH wrote:
>>> On Tue, Feb 12, 2019 at 06:29:39PM +0800, Kyle Tso wrote:
>>>> On Thu, Jan 31, 2019 at 3:02 PM Greg KH <gregkh@...uxfoundation.org>
>> wrote:
>>>>
>>>>> On Thu, Jan 31, 2019 at 11:54:11AM +0800, Kyle Tso wrote:
>>>>>> Provide a function to get the partner Source Capabilities.
>>>>>>
>>>>>> Signed-off-by: Kyle Tso <kyletso@...gle.com>
>>>>>> ---
>>>>>>    drivers/usb/typec/tcpm/tcpm.c | 23 +++++++++++++++++++++++
>>>>>>    include/linux/usb/tcpm.h      |  1 +
>>>>>>    2 files changed, 24 insertions(+)
>>>>>>
>>>>>> diff --git a/drivers/usb/typec/tcpm/tcpm.c
>>>>> b/drivers/usb/typec/tcpm/tcpm.c
>>>>>> index f1d3e54210df..29cd84ba9960 100644
>>>>>> --- a/drivers/usb/typec/tcpm/tcpm.c
>>>>>> +++ b/drivers/usb/typec/tcpm/tcpm.c
>>>>>> @@ -4494,6 +4494,29 @@ int tcpm_update_sink_capabilities(struct
>>>>> tcpm_port *port, const u32 *pdo,
>>>>>>    }
>>>>>>    EXPORT_SYMBOL_GPL(tcpm_update_sink_capabilities);
>>>>>>
>>>>>> +/*
>>>>>> + * Don't call this function in interrupt context. Caller needs to
>>>>>> +free
>>>>> the
>>>>>> + * memory itself.
>>>>>> + */
>>>>>> +int tcpm_get_partner_src_caps(struct tcpm_port *port, u32
>>>>>> +**src_pdo) {
>>>>>> +     unsigned int nr_pdo;
>>>>>> +
>>>>>> +     if (port->nr_source_caps == 0)
>>>>>> +             return -ENODATA;
>>>>>> +
>>>>>> +     *src_pdo = kcalloc(port->nr_source_caps, sizeof(u32), GFP_KERNEL);
>>>>>> +     if (!src_pdo)
>>>>>> +             return -ENOMEM;
>>>>>> +
>>>>>> +     mutex_lock(&port->lock);
>>>>>> +     nr_pdo = tcpm_copy_pdos(*src_pdo, port->source_caps,
>>>>>> +                             port->nr_source_caps);
>>>>>> +     mutex_unlock(&port->lock);
>>>>>> +     return nr_pdo;
>>>>>> +}
>>>>>> +EXPORT_SYMBOL_GPL(tcpm_get_partner_src_caps);
>>>>>
>>>>> We don't add new functions that no one uses :(
>>>>>
>>>>>
>>>> This function is useful if the PD Device Policy Manager is
>>>> implemented outside of TCPM.
>>>> In this situation, Device Policy Manager needs to know the partner
>>>> capabilities to optimize the charging process.
>>>
>>> And where is that code?
>>>
>>
>> Agreed - that code should be sent upstream as well to let us see the entire
>> context.
>>
>>>> Take existing functions in TCPM for example:
>>>> Function "tcpm_update_sink_capabilities" and
>>>> "tcpm_update_source_capabilities" are exposed as well. And no one
>>>> uses them now.
>>>
>>> Great, let's go delete them now, we should not have apis that no one
>>> uses.  This isn't a new thing...
>>>
>>
>> I sent a patch to do just that. Quite frankly I don't recal why I thought those
>> functions might be needed.
> 
> As a mind jog - https://lkml.org/lkml/2017/11/27/1256 :)
> 

Nice find. However, since the code using it was never implemented, I think it
is prudent at this point to remove the code. It can be reintroduced if/when needed,
and at that point be tested properly.

Thanks,
Guenter