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Message-ID: <cb640534-ed9f-4b69-8070-6eb3efd72604@t-8ch.de>
Date: Fri, 10 Feb 2023 11:36:02 -0700 (GMT-07:00)
From: Thomas Weißschuh <thomas@...ch.de>
To: Aditya Garg <gargaditya08@...e.com>
Cc: Jiri Kosina <jikos@...nel.org>, jkosina@...e.cz,
benjamin.tissoires@...hat.com,
Andy Shevchenko <andy@...radead.org>,
andy.shevchenko@...il.com, LKML <linux-kernel@...r.kernel.org>,
linux-input@...r.kernel.org, ronald@...ovation.ch,
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.
Feb 10, 2023 08:50:12 Aditya Garg <gargaditya08@...e.com>:
>
>
>> 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;
I would prefer
if (!hid_is_usb(hdev))
return -EINVAL;
udev = hid_to_usb_dev(hdev);
>
> 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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