linux-kernel - Re: [PATCH v2 3/3] gpio: pcf857x: Add OF support

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Date:	Sun, 25 Aug 2013 10:04:38 +0200
From:	Sylwester Nawrocki <sylvester.nawrocki@...il.com>
To:	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	Tomasz Figa <tomasz.figa@...il.com>
CC:	Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
	linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
	devicetree@...r.kernel.org,
	Linus Walleij <linus.walleij@...aro.org>,
	swarren@...dotorg.org, ian.campbell@...rix.com,
	mark.rutland@....com, pawel.moll@....com, galak@...eaurora.org,
	rob.herring@...xeda.com
Subject: Re: [PATCH v2 3/3] gpio: pcf857x: Add OF support

On 08/25/2013 02:15 AM, Laurent Pinchart wrote:
> On Saturday 24 August 2013 16:13:11 Tomasz Figa wrote:
>> On Saturday 24 of August 2013 02:54:07 Laurent Pinchart wrote:
>>> On Saturday 24 August 2013 02:41:59 Tomasz Figa wrote:
>>>> On Tuesday 20 of August 2013 01:04:54 Laurent Pinchart wrote:
>>>>> Add DT bindings for the pcf857x-compatible chips and parse the
>>>>> device tree node in the driver.
>>>>>
>>>>> Signed-off-by: Laurent Pinchart
>>>>> <laurent.pinchart+renesas@...asonboard.com>  ---
>>>>>
>>>>>   .../devicetree/bindings/gpio/gpio-pcf857x.txt      | 71 +++++++++++++
>>>>>   drivers/gpio/gpio-pcf857x.c                        | 57 ++++++++++---
>>>>>   2 files changed, 119 insertions(+), 9 deletions(-)
>>>>>   create mode 100644
>
> [snip]
>
>>>>> diff --git a/drivers/gpio/gpio-pcf857x.c
>>>>> b/drivers/gpio/gpio-pcf857x.c
>>>>> index 070e81f..50a90f1 100644
>>>>> --- a/drivers/gpio/gpio-pcf857x.c
>>>>> +++ b/drivers/gpio/gpio-pcf857x.c
>>>
>>> [snip]
>>>
>>>>> @@ -50,6 +52,27 @@ static const struct i2c_device_id pcf857x_id[] =
>>>>> {
>>>>>
>>>>>   };
>>>>>   MODULE_DEVICE_TABLE(i2c, pcf857x_id);
>>>>>
>>>>> +#ifdef CONFIG_OF
>>>>> +static const struct of_device_id pcf857x_of_table[] = {
>>>>> +	{ .compatible = "nxp,pcf8574", .data = (void *)8 },
>>>>> +	{ .compatible = "nxp,pcf8574a", .data = (void *)8 },
>>>>> +	{ .compatible = "nxp,pca8574", .data = (void *)8 },
>>>>> +	{ .compatible = "nxp,pca9670", .data = (void *)8 },
>>>>> +	{ .compatible = "nxp,pca9672", .data = (void *)8 },
>>>>> +	{ .compatible = "nxp,pca9674", .data = (void *)8 },
>>>>> +	{ .compatible = "nxp,pcf8575", .data = (void *)16 },
>>>>> +	{ .compatible = "nxp,pca8575", .data = (void *)16 },
>>>>> +	{ .compatible = "nxp,pca9671", .data = (void *)16 },
>>>>> +	{ .compatible = "nxp,pca9673", .data = (void *)16 },
>>>>> +	{ .compatible = "nxp,pca9675", .data = (void *)16 },
>>>>> +	{ .compatible = "maxim,max7328", .data = (void *)8 },
>>>>> +	{ .compatible = "maxim,max7329", .data = (void *)8 },
>>>>> +	{ .compatible = "ti,tca9554", .data = (void *)8 },
>>>>> +	{ }
>>>>> +};
>>>>> +MODULE_DEVICE_TABLE(of, pcf857x_of_table);
>>>>> +#endif
>>>>> +
>>>>>
>>>>>   /*
>>>>>    * The pcf857x, pca857x, and pca967x chips only expose one read and
>>>>>    * one write register.  Writing a "one" bit (to match the reset
>>>>> @@ -257,14 +280,29 @@ fail:
>>>>>   static int pcf857x_probe(struct i2c_client *client,
>>>>>   			 const struct i2c_device_id *id)
>>>>>   {
>>>>> -	struct pcf857x_platform_data	*pdata;
>>>>> +	struct pcf857x_platform_data	*pdata = client->dev.platform_data;
>>>>> +	struct device_node		*np = client->dev.of_node;
>   >  >  >   	struct pcf857x			*gpio;
>>>>> +	unsigned int			n_latch = 0;
>>>>> +	unsigned int			ngpio;
>>>>>   	int				status;
>>>>>
>>>>> -	pdata = client->dev.platform_data;
>>>>> -	if (!pdata) {
>>>>> +#ifdef CONFIG_OF
>>>>> +	if (np) {
>>>>
>>>> Wouldn't if (IS_ENABLED(CONFIG_OF)&&  np) be sufficient here, without
>>>> the #ifdef? You would have to move the match table out of the #ifdef
>>>> in this case, though...
>>>
>>> That's the exact reason why I've used #ifdef CONFIG_OF here, I didn't
>>> want to add the overhead of the pcf857x_of_table when CONFIG_OF isn't
>>> defined.
>>
>> I'm not sure if I remember correctly, but I think there was something said
>> in one of discussions some time ago, that we should be moving away from
>> ifdef'ing such things, in favour of just having them compiled
>> unconditionally.
>
> There seems to be a general consensus to favor if (IS_ENABLED(CONFIG_OF))
> instead of #ifdef CONFIG_OF when possible. I'm not sure what the opinion is
> regarding using conditional compilation to avoid compiling unnecessary data
> tables in. I would vote for using it (there's no need to bloat the kernel
> unnecessarily on non-OF platforms), but I'll conform to whatever is decided to
> be best.
>
>> [Adding DT maintainers on Cc for more opinions.]
>
> I'll resubmit the patch with the DT bindings documentation fixed, and will
> submit yet another version if I need to remove the #ifdef.

I think it makes sense to keep this table compiled in conditionally, 
size of
struct of_device_id is relatively large. While absolute increase in size
might not be that significant the relative increase is quite large - 
appr. 130%.


Before $subject patch:

$ size drivers/gpio/gpio-pcf857x.o
    text	   data	    bss	    dec	    hex	filename
    2228	    140	      0	   2368	    940	drivers/gpio/gpio-pcf857x.o

After applying the patch:

$ size drivers/gpio/gpio-pcf857x.o
    text	   data	    bss	    dec	    hex	filename
    5284	    140	      0	   5424	   1530	drivers/gpio/gpio-pcf857x.o

--
Regards,
Sylwester
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