linux-kernel - Re: [greybus-dev] [PATCH] staging: greybus: Use gpio_is

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Date:   Sat, 28 Apr 2018 10:00:15 +0530
From:   arvindY <arvind.yadav.cs@...il.com>
To:     Alex Elder <elder@...aro.org>, hvaibhav.linux@...il.com,
        johan@...nel.org, elder@...nel.org, gregkh@...uxfoundation.org
Cc:     devel@...verdev.osuosl.org, greybus-dev@...ts.linaro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [greybus-dev] [PATCH] staging: greybus: Use gpio_is_valid()



On Friday 27 April 2018 06:32 PM, Alex Elder wrote:
> On 04/27/2018 07:50 AM, Arvind Yadav wrote:
>>
>> On Friday 27 April 2018 05:47 PM, Alex Elder wrote:
>>> On 04/27/2018 05:52 AM, Arvind Yadav wrote:
>>>> Replace the manual validity checks for the GPIO with the
>>>> gpio_is_valid().
>>> I haven't looked through the code paths very closely, but I
>>> think that get_named_gpio() might return -EPROBE_DEFER, which
>>> would be something we want to pass to the caller.
>> Yes of_get_name_gpio() can return other error value apart from
>> -EPROBE_DEFER.
>>> So rather than returning -ENODEV and hiding the reason the
>>> call to of_get_named_gpio() failed, you should continue
>>> returning the errno it supplies (if not a valid gpio number).
>>>
>>>                      -Alex
>> I have return -ENODEV because invalid gpio pin can be positive.
>> static inline bool gpio_is_valid(int number)
>> {
>>      return number >= 0 && number < ARCH_NR_GPIOS;
>> }
>> Here if number > ARCH_NR_GPIOS then it's invalid but return value
>> will be positive.
> Your reasoning is good.  However in all three of these cases,
> the GPIO number you're checking is the value returned from
> of_get_named_gpio().  The return value is a "GPIO number to
> use with Linux generic GPIO API, or one of the errno value."
>
> So unless the API of of_get_named_gpio() changes, you can be
> sure that if the value returned is invalid, it is a negative
> errno.  (And if the API did change, the person making that
> change would be responsible for fixing all callers to ensure
> the change didn't break them.)
>
> This distinction may be why the code you're changing was only
> testing for negative, rather than using gpio_is_valid() (you'll
> see it's used elsewhere in the Greybus code--even in the same
> source files.)
>
> Anyway, changing the code to use gpio_is_valid() is fine.  But
> you should avoid obscuring the reason for the error that the
> return value from of_get_named_gpio() provides.
>
> 					-Alex

Yes, It'll be fine to return a invalid gpio as error instead of
-ENODEV. I will send an updated patch.

~arvind
>
>> We can return like this
>>      " return (gpio > 0) ? -ENODEV: gpio;"
>>
>> But not sure this is worth to handle this.
>>
>> ~arvind
>>>> Signed-off-by: Arvind Yadav <arvind.yadav.cs@...il.com>
>>>> ---
>>>>    drivers/staging/greybus/arche-platform.c | 12 ++++++------
>>>>    1 file changed, 6 insertions(+), 6 deletions(-)
>>>>
>>>> diff --git a/drivers/staging/greybus/arche-platform.c b/drivers/staging/greybus/arche-platform.c
>>>> index 83254a7..fc6bf60 100644
>>>> --- a/drivers/staging/greybus/arche-platform.c
>>>> +++ b/drivers/staging/greybus/arche-platform.c
>>>> @@ -448,9 +448,9 @@ static int arche_platform_probe(struct platform_device *pdev)
>>>>        arche_pdata->svc_reset_gpio = of_get_named_gpio(np,
>>>>                                "svc,reset-gpio",
>>>>                                0);
>>>> -    if (arche_pdata->svc_reset_gpio < 0) {
>>>> +    if (!gpio_is_valid(arche_pdata->svc_reset_gpio)) {
>>>>            dev_err(dev, "failed to get reset-gpio\n");
>>>> -        return arche_pdata->svc_reset_gpio;
>>>> +        return -ENODEV;
>>>>        }
>>>>        ret = devm_gpio_request(dev, arche_pdata->svc_reset_gpio, "svc-reset");
>>>>        if (ret) {
>>>> @@ -468,9 +468,9 @@ static int arche_platform_probe(struct platform_device *pdev)
>>>>        arche_pdata->svc_sysboot_gpio = of_get_named_gpio(np,
>>>>                                  "svc,sysboot-gpio",
>>>>                                  0);
>>>> -    if (arche_pdata->svc_sysboot_gpio < 0) {
>>>> +    if (!gpio_is_valid(arche_pdata->svc_sysboot_gpio)) {
>>>>            dev_err(dev, "failed to get sysboot gpio\n");
>>>> -        return arche_pdata->svc_sysboot_gpio;
>>>> +        return -ENODEV;
>>>>        }
>>>>        ret = devm_gpio_request(dev, arche_pdata->svc_sysboot_gpio, "sysboot0");
>>>>        if (ret) {
>>>> @@ -487,9 +487,9 @@ static int arche_platform_probe(struct platform_device *pdev)
>>>>        arche_pdata->svc_refclk_req = of_get_named_gpio(np,
>>>>                                "svc,refclk-req-gpio",
>>>>                                0);
>>>> -    if (arche_pdata->svc_refclk_req < 0) {
>>>> +    if (!gpio_is_valid(arche_pdata->svc_refclk_req)) {
>>>>            dev_err(dev, "failed to get svc clock-req gpio\n");
>>>> -        return arche_pdata->svc_refclk_req;
>>>> +        return -ENODEV;
>>>>        }
>>>>        ret = devm_gpio_request(dev, arche_pdata->svc_refclk_req,
>>>>                    "svc-clk-req");
>>>>