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

[Eric Miao]

On Tue, Jun 22, 2010 at 12:00 PM, Joonyoung Shim
<jy0922.shim at samsung.com> wrote:
> On 6/22/2010 12:38 PM, Eric Miao wrote:
>> On Tue, Jun 22, 2010 at 11:27 AM, Joonyoung Shim
>> <jy0922.shim at samsung.com> wrote:
>>> On 6/22/2010 12:02 PM, Eric Miao wrote:
>>>> On Tue, Jun 22, 2010 at 8:48 AM, Joonyoung Shim <jy0922.shim at samsung.com> wrote:
>>>>> 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 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.
>>>>>> 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.
>>>>>
>>>> This is a generic issue. Even if in your example, you can avoid this by
>>>> re-allocation and re-assignment (ignore the performance issue for such
>>>> behavior), the real question is the difficult to track all these down. Since
>>> Right, it can occur difficulty of maintain. I wanted just to inform the
>>> current fact.
>>>
>>>> matrix_keypad_data is something out of your control (it was actually
>>>> drafted by me and Dmitry if you are interested), and think about one day
>>>> I changed it's definition, now you have to sync your driver and code every
>>>> time to make sure the discarded data is not referenced.
>>>>
>>> if matrix_keypad_data is changed, i think the patchset should included
>>> change of related other parts using it.
>>>
>>
>> That's reasonable but difficult in practice, every keypad driver using
>> matrix_keypad_data could be doing things differently. That's what I'm
>
> Just FYI, correct name is matrix_keymap_data and current all keypad
> drivers using matrix_keymap_data use it to same way.
>

Note I was just thinking there is a potential issue as been pointed out that
we can improve. And I'm not NACKing your perfect patch. Sorry if I made
you think so.