linux-kernel - Re: [1/5] i2c: i2c-davinci: switch to use platform_get

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Date:	Fri, 21 Nov 2014 16:59:19 +0200
From:	Grygorii Strashko <grygorii.strashko@...com>
To:	Rob Herring <robherring2@...il.com>
CC:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Grant Likely <grant.likely@...aro.org>,
	Wolfram Sang <wsa@...-dreams.de>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Sekhar Nori <nsekhar@...com>,
	Kevin Hilman <khilman@...prootsystems.com>,
	Santosh Shilimkar <ssantosh@...nel.org>,
	Murali Karicheri <m-karicheri2@...com>
Subject: Re: [1/5] i2c: i2c-davinci: switch to use platform_get_irq

On 11/21/2014 04:03 PM, Rob Herring wrote:
> On Fri, Nov 21, 2014 at 5:01 AM, Grygorii Strashko
> <grygorii.strashko@...com> wrote:
>> On 11/20/2014 11:48 PM, Uwe Kleine-König wrote:
>>> Hello Grygorii,
>>>
>>> On Thu, Nov 20, 2014 at 12:03:04PM +0200, Grygorii Strashko wrote:
>>>> Switch Davinci I2C driver to use platform_get_irq(), because
>>>> - it is not recommened to use
>>>>     platform_get_resource(pdev, IORESOURCE_IRQ, ..) for requesting IRQ's
>>>>     resources any more, as they can be not ready yet in case of DT-booting.
>>>> - it makes code simpler
>>>>
>>>> CC: Sekhar Nori <nsekhar@...com>
>>>> CC: Kevin Hilman <khilman@...prootsystems.com>
>>>> CC: Santosh Shilimkar <ssantosh@...nel.org>
>>>> CC: Murali Karicheri <m-karicheri2@...com>
>>>> Signed-off-by: Grygorii Strashko <grygorii.strashko@...com>
>>>> ---
>>>>    drivers/i2c/busses/i2c-davinci.c | 14 +++++++-------
>>>>    1 file changed, 7 insertions(+), 7 deletions(-)
>>>>
>>>> diff --git a/drivers/i2c/busses/i2c-davinci.c b/drivers/i2c/busses/i2c-davinci.c
>>>> index 4d96147..9bbfb8f 100644
>>>> --- a/drivers/i2c/busses/i2c-davinci.c
>>>> +++ b/drivers/i2c/busses/i2c-davinci.c
>>>> @@ -640,13 +640,13 @@ static int davinci_i2c_probe(struct platform_device *pdev)
>>>>    {
>>>>       struct davinci_i2c_dev *dev;
>>>>       struct i2c_adapter *adap;
>>>> -    struct resource *mem, *irq;
>>>> -    int r;
>>>> +    struct resource *mem;
>>>> +    int r, irq;
>>>>
>>>> -    irq = platform_get_resource(pdev, IORESOURCE_IRQ, 0);
>>>> -    if (!irq) {
>>>> -            dev_err(&pdev->dev, "no irq resource?\n");
>>>> -            return -ENODEV;
>>>> +    irq = platform_get_irq(pdev, 0);
>>> One bad thing about platform_get_irq is its unusual handling of irq=0.
>>> I'm pretty sure you don't want to use this value, so adding something
>>> like:
>>>
>>>        if (!irq)
>>>                irq = -ENXIO

I'll add this check in driver.

>>>
>>> would be welcome because the usual value for "invalid irq" is 0 and not
>>> -ESOMETHING. platform_get_irq is one of the very few functions that
>>> don't adhere to this convention. With handling <= 0 as error your code
>>> is immune to changes in this area. Although I notice that
>>> platform_get_irq got worse in this respect to handle -EPROBE_DEFER. hmm.
>>>
>>> Apart from your change I wonder if platform_get_irq should handle
>>> of_irq_get returning 0 as an error.
>>
>> I think you are right and It seems like, the check for !irq should
>> be added/restored for OF case in platform_get_irq() too.
>
> Changing the return values of platform_get_irq is tricky as it would
> potentially break drivers because NO_IRQ can be 0 or -1 depending on
> the arch. Drivers checking against specific values of NO_IRQ would
> break. We've done some clean-up in this area, but I suspect more is
> needed.

Thanks for your comment.

regards,
-grygorii
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