2012/12/11 Anisse Astier <anisse@xxxxxxxxx>:
> On Tue, 11 Dec 2012 19:07:51 +0200, Maxim Mikityanskiy <maxtram95@xxxxxxxxx> wrote :
>
>> >> @@ -169,11 +169,15 @@ static void msi_wmi_notify(u32 value, void *context)
>> >> pr_debug("Eventcode: 0x%x\n", eventcode);
>> >> key = sparse_keymap_entry_from_scancode(msi_wmi_input_dev,
>> >> eventcode);
>> >> - if (key) {
>> >> + if (!key) {
>> >> + pr_info("Unknown key pressed - %x\n", eventcode);
>> >> + goto msi_wmi_notify_exit;
>> >> + }
>> >> + if (quirk_last_pressed) {
>> >> + size_t key_index = key - msi_wmi_keymap;
>> > Do you mean key->code - MSI_SCANCODE_BASE ? I'm not sure I understand the
>> > intent here otherwise.
>>
>> msi_wmi_keymap is array of 'struct key_entry', i.e. pointer to array's
>> first item. key is a pointer to some array's item. So 'key -
>> msi_wmi_keymap' is a difference between pointers, i.e. index of key in
>> msi_wmi_keymap.
>>
>> I do pointer arithmetic here because in patch 12 I add some new
>> scancodes, and holes appear in scancode sequence, so we can't just use
>> 'key->code - MSI_SCANCODE_BASE' to get item index in array.
>
> Oh, I see. This is very clever, but a bit too clever. You have no
> guarantee, that sparse_keymap_entry_from_scancode will give you a pointer
> to *your* key_entry. In fact, it doesn't.
>
> In sparse_keymap_setup (drivers/input/sparse-keymap.c), the keymap
> array(msi_wmi_keymap) is mempcy-ed, at line 187 (kernel ~3.7). So if you
> want to use this method, you might need to re-compute the index by
> iterating over the elements and comparing key->code for each.
Oops, I'm sorry, I was looking only into
sparse_keymap_entry_from_scancode() and I didn't discover the fact
that dev->keycode is not equal to msi_wmi_keymap. I just wanted to
avoid iterating through the array second time. Also, can I use
msi_wmi_input_dev->keycode instead of msi_wmi_keymap as array base?
input_dev::keycode field is documented at include/linux/input.h:62.
It's strange that I didn't get a crash or data corruption on my system
when I forced usage of last_pressed for my laptop, loaded this module
and tried to press keys.
It's very unconvenient that struct key_entry does not have some field
for driver-specific extra data. In such field we could store index in
last_pressed or event last press time. But we haven't such field.
>
> Regards,
>
> Anisse
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