linux-kernel - Re: [PATCH v2] serdev: Replace serdev_device_write_buf with serdev_device

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Date:   Thu, 30 Mar 2017 05:41:37 -0700
From:   Andrey Smirnov <andrew.smirnov@...il.com>
To:     Rob Herring <robh@...nel.org>
Cc:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Chris Healy <cphealy@...il.com>,
        Guenter Roeck <linux@...ck-us.net>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] serdev: Replace serdev_device_write_buf with serdev_device_write

On Wed, Mar 29, 2017 at 2:25 PM, Rob Herring <robh@...nel.org> wrote:
> On Wed, Mar 29, 2017 at 9:16 AM, Andrey Smirnov
> <andrew.smirnov@...il.com> wrote:
>> On Tue, Mar 28, 2017 at 10:07 AM, Andy Shevchenko
>> <andy.shevchenko@...il.com> wrote:
>>> On Tue, Mar 28, 2017 at 7:01 PM, Andrey Smirnov
>>> <andrew.smirnov@...il.com> wrote:
>>>> Convert serdev_device_write_buf's code to be able to transfer amount of
>>>> data potentially exceeding "write room" at the moment of invocation.
>>>>
>>>> To support that, also add serdev_device_write_wakeup.
>>>>
>>>> Drivers wanting to use full extent of serdev_device_write
>>>> functionality are expected to provide serdev_device_write_wakeup as a
>>>> sole handler of .write_wakeup event or call it as a part of driver's
>>>> custom .write_wakeup code.
>>>>
>>>> Drivers wanting to retain old serdev_device_write_buf behaviour can
>>>
>>>> replace those call to calls to serdev_device_write with timeout of
>>>> 0. Providing .write_wakeup handler in such case is optional.
>>>
>>> Some indentation would be better if, for example, 0 will be kept on
>>> previous line.
>>>
>>
>> OK, sure.
>>
>>> So, what I would see if no one objects is patch series of two:
>>> 1) introduction of new API
>>> 2) removing old one.
>>>
>>> It will benefit for easier review and any potential code anthropologist.
>>>
>>
>> Second version of the patch preserves the old API an just
>> re-implements it in terms of a new one. I am not sure I see the
>> benefit in splitting it into two patches, but I'll leave it up to Rob
>> to decide.
>
> I think it is fine as-is, but maybe the subject now is a bit misleading.
>

OK, I'll modify the subject to be more representative of the change.

>>>> --- a/drivers/tty/serdev/core.c
>>>> +++ b/drivers/tty/serdev/core.c
>>>> @@ -116,17 +116,41 @@ void serdev_device_close(struct serdev_device *serdev)
>>>>  }
>>>>  EXPORT_SYMBOL_GPL(serdev_device_close);
>>>>
>>>> -int serdev_device_write_buf(struct serdev_device *serdev,
>>>> -                           const unsigned char *buf, size_t count)
>>>> +void serdev_device_write_wakeup(struct serdev_device *serdev)
>>>> +{
>>>> +       complete(&serdev->write_comp);
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(serdev_device_write_wakeup);
>>>> +
>>>> +int serdev_device_write(struct serdev_device *serdev,
>>>> +                       const unsigned char *buf, size_t count,
>>>> +                       unsigned long timeout)
>>>>  {
>>>>         struct serdev_controller *ctrl = serdev->ctrl;
>>>> +       int ret;
>>>>
>>>> -       if (!ctrl || !ctrl->ops->write_buf)
>>>> +       if (!ctrl || !ctrl->ops->write_buf ||
>>>> +           (timeout && !serdev->ops->write_wakeup))
>>>>                 return -EINVAL;
>>>>
>>>> -       return ctrl->ops->write_buf(ctrl, buf, count);
>>>> +       mutex_lock(&serdev->write_lock);
>>>> +       do {
>>>> +               reinit_completion(&serdev->write_comp);
>>>> +
>>>> +               ret = ctrl->ops->write_buf(ctrl, buf, count);
>>>> +               if (ret < 0)
>>>> +                       break;
>>>> +
>>>
>>>> +               buf   += ret;
>>>
>>> Extra white spaces.
>>
>> Which is there on purpose to re-align "+=" with "-=" on the next line.
>> I'll remove it.
>>
>>>
>>>> +               count -= ret;
>>>> +
>>>
>>>> +       } while (count &&
>>>> +                (timeout = wait_for_completion_timeout(&serdev->write_comp,
>>>> +                                                       timeout)));
>>>
>>> So, would it be better to support interrupts here and return a
>>> corresponding error code to the user?
>>>
>>
>> I don't have a use-case for that and as far as I can tell, neither SPI
>> nor I2C slave device API offer such functionality universally, so I am
>> inclined to say no. Since the change from wait_for_completion to
>> wait_for_completion_timeout was made per Rob's request, I'd leave it
>> up to him to decided about this change as well.
>
> Honestly, I don't know. It's added easily enough if needed later.

OK, I'll keep things as is for now.

Thanks,
Andrey Smirnov