[PATCH v5 1/3] ARM: SAMSUNG: Add keypad device support

[Eric Miao]

On Mon, Jun 21, 2010 at 5:19 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Mon, Jun 21, 2010 at 05:05:34PM +0800, Eric Miao wrote:
>> On Mon, Jun 21, 2010 at 2:26 PM, Joonyoung Shim <jy0922.shim at samsung.com> wrote:
>> > +void __init samsung_keypad_set_platdata(struct samsung_keypad_platdata *pd)
>> > +{
>> > +       struct samsung_keypad_platdata *npd;
>> > +
>> > +       if (!pd) {
>> > +               printk(KERN_ERR "%s: no platform data\n", __func__);
>> > +               return;
>> > +       }
>> > +
>> > +       npd = kmemdup(pd, sizeof(struct samsung_keypad_platdata), GFP_KERNEL);
>> > +       if (!npd)
>> > +               printk(KERN_ERR "%s: no memory for platform data\n", __func__);
>>
>> This part of the code is actually duplicated again and again and again
>> for each device, PXA and other legacy platforms are bad references for
>> this. In arch/arm/mach-mmp/, it might be a bit cleaner, there are three
>> major points:
>>
>>  1. A minimum 'struct pxa_device_desc' for a simple description of a
>>     device (more than 90% of the devices can be described that way),
>>     and avoid using a comparatively heavier weight platform_device,
>>     which can be generated at run-time
>>
>>  2. pxa_register_device() to allocate and register the platform_device
>>     at run-time, along with the platform data
>
> It's a bad idea to make platform data be run-time discardable like this:
>
>> > +struct samsung_keypad_platdata {
>> > +       const struct matrix_keymap_data *keymap_data;
>
> What you end up with is some platform data structures which must be kept
> (those which have pointers to them from the platform data), and others
> (the platform data itself) which can be discarded at runtime.
>
> We know that the __initdata attributations cause lots of problems -
> they're frequently wrong.  Just see the constant hastle with __devinit
> et.al.  The same issue happens with __initdata as well.
>
> So why make things more complicated by allowing some platform data
> structures to be discardable and others not to be?  Is their small
> size (maybe 6 words for this one) really worth the hastle of getting
> __initdata attributations wrong (eg, on the keymap data?)
>

Russell,

The benefit I see is when multiple boards are compiled in, those
data not used can be automatically discarded.