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

[Joonyoung Shim <jy0922.shim@samsung.com>]

On 6/21/2010 8:16 PM, Russell King - ARM Linux wrote:
> On Mon, Jun 21, 2010 at 06:39:10PM +0800, Eric Miao wrote:
>> On Mon, Jun 21, 2010 at 5:19 PM, Russell King - ARM Linux
>> <linux@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@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.
> 
> Yes, but only some of the data can be discarded.  Continuing with the
> example in hand, while you can discard the six words which represent
> samsung_keypad_platdata, but the keymap_data can't be because that won't
> be re-allocated, which is probably a much larger data structure.
> 

No. the keymap_data is possible too. The keypad driver allocates other
keymap area of input device and it is assigned from datas based on this
keymap_data.