Date:   Fri, 10 Feb 2023 15:49:59 +0000
From:   Aditya Garg <gargaditya08@...e.com>
To:     Thomas Weißschuh <thomas@...ch.de>
CC:     Jiri Kosina <jikos@...nel.org>,
        "jkosina@...e.cz" <jkosina@...e.cz>,
        "benjamin.tissoires@...hat.com" <benjamin.tissoires@...hat.com>,
        Andy Shevchenko <andy@...radead.org>,
        "andy.shevchenko@...il.com" <andy.shevchenko@...il.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "linux-input@...r.kernel.org" <linux-input@...r.kernel.org>,
        "ronald@...ovation.ch" <ronald@...ovation.ch>,
        "kekrby@...il.com" <kekrby@...il.com>,
        Orlando Chamberlain <orlandoch.dev@...il.com>
Subject: Re: [PATCH 1/3] HID: apple-ibridge: Add Apple iBridge HID driver for
 T1 chip.



> On 10-Feb-2023, at 9:04 PM, Thomas Weißschuh <thomas@...ch.de> wrote:
> 
> Responses inline
> 
> On Fri, Feb 10, 2023 at 12:05:13PM +0000, Aditya Garg wrote:
>>>> On 10-Feb-2023, at 10:26 AM, Thomas Weißschuh <thomas@...ch.de> wrote:
>>> 
>>> Hi,
>>> 
>>> some comments inline.
>>> 
>>>> On Fri, Feb 10, 2023 at 03:43:24AM +0000, Aditya Garg wrote:
>>> 
>>>> +
>>>> +static struct {
>>>> + unsigned int usage;
>>>> + struct hid_device_id *dev_id;
>>>> +} appleib_usage_map[] = {
>>>> + /* Default iBridge configuration, key inputs and mode settings */
>>>> + { 0x00010006, &appleib_sub_hid_ids[0] },
>>>> + /* OS X iBridge configuration, digitizer inputs */
>>>> + { 0x000D0005, &appleib_sub_hid_ids[0] },
>>>> + /* All iBridge configurations, display/DFR settings */
>>>> + { 0xFF120001, &appleib_sub_hid_ids[0] },
>>>> + /* All iBridge configurations, ALS */
>>>> + { 0x00200041, &appleib_sub_hid_ids[1] },
>>>> +};
>>> 
>>> const
>>> 
>> 
>> Constantifying this results in compiler giving warnings
>> 
>> drivers/hid/apple-ibridge.c:78:23: warning: initialization discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
>>   78 |         { 0x00200041, &appleib_sub_hid_ids[1] },
> 
> For this you also have to constify the hid_device_id *dev_id in
> appleib_usage_map. And then propagate this change to some functions and
> variables.
> 
>>      |                       ^
>> drivers/hid/apple-ibridge.c: In function 'appleib_add_sub_dev':
>> drivers/hid/apple-ibridge.c:363:29: warning: assignment discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
>>  363 |         sub_hdev->ll_driver = &appleib_ll_driver;
> 
> As Benjamin said this is because your changes are based on Linus' tree
> but they will break as soon as they will be merged into the HID tree.
> You should base your changes off of the HID tree:
> https://git.kernel.org/pub/scm/linux/kernel/git/hid/hid.git/log/?h=for-6.3/hid-core
> 
> This issue is essentially unlucky timing.
> 
>>      |                             ^
>> drivers/hid/apple-ibridge.c: In function 'appleib_hid_probe':
>> drivers/hid/apple-ibridge.c:436:12: error: expected '(' before 'hid_is_usb'
>>  436 |         if hid_is_usb(hdev)
>>      |            ^~~~~~~~~~
>>      |            (
> 
> As the error message indicates, this is invalid syntax and missing a
> '('.
> What you want to do is to check for 
> 
>  if (!hid_is_usb(hdev))
>    return -ENODEV;

It was a typo on my part

+	/* check and set usb config first */
+	if (hid_is_usb(hdev))
+		udev = hid_to_usb_dev(hdev);
+	else
+		return -EINVAL;

This is what I have in my patch set now.

If there is something wrong with this, then do tell me

Thanks
> 
> *before* calling hid_to_usb_dev(hdev);
> 
>> In file included from drivers/hid/apple-ibridge.c:48:
>> drivers/hid/apple-ibridge.c: In function 'appleib_probe':
>> drivers/hid/apple-ibridge.c:544:35: warning: passing argument 1 of '__hid_register_driver' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
>>  544 |         ret = hid_register_driver(&appleib_hid_driver);
>>      |                                   ^~~~~~~~~~~~~~~~~~~
>> ./include/linux/hid.h:898:31: note: in definition of macro 'hid_register_driver'
>>  898 |         __hid_register_driver(driver, THIS_MODULE, KBUILD_MODNAME)
>>      |                               ^~~~~~
>> ./include/linux/hid.h:893:47: note: expected 'struct hid_driver *' but argument is of type 'const struct hid_driver *'
>>  893 | extern int __must_check __hid_register_driver(struct hid_driver *,
>>      |                                               ^~~~~~~~~~~~~~~~~~~
>> drivers/hid/apple-ibridge.c: In function 'appleib_remove':
>> drivers/hid/apple-ibridge.c:558:31: warning: passing argument 1 of 'hid_unregister_driver' discards 'const' qualifier from pointer target type [-Wdiscarded-qualifiers]
>>  558 |         hid_unregister_driver(&appleib_hid_driver);
>>      |                               ^~~~~~~~~~~~~~~~~~~
>> ./include/linux/hid.h:900:35: note: expected 'struct hid_driver *' but argument is of type 'const struct hid_driver *'
>>  900 | extern void hid_unregister_driver(struct hid_driver *);
>>      |                                   ^~~~~~~~~~~~~~~~~~~
> 
> These are all because applib_hid_driver can not be const.
> Sorry for the wrong advice.
> 
> Benjamin:
> HID drivers can not be const because they embed a 'struct driver' that
> is needed by the driver core to be mutable.
> Fixing this is probably a larger enterprise.
> 
>> make[6]: *** [scripts/Makefile.build:250: drivers/hid/apple-ibridge.o] Error 1
>> make[5]: *** [scripts/Makefile.build:500: drivers/hid] Error 2
>> make[5]: *** Waiting for unfinished jobs….
>> 
>> Some warnings are also due to a typo in if and constantifying `static struct hid_driver`, although they probably can
>> be fixed.
>> 
>> In short, Thomas, do you really want me to constantify the structure I
>> am talking about in this email, as well `static struct hid_driver`?
> 
> struct hid_driver: Don't constify
> all others: Do constify
> 
> Thomas

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