linux-kernel - Re: [PATCH v4 2/2] drm/tiny: add driver for Apple Touch Bars in x86 Macs

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Message-ID:
 <PN3PR01MB959735D463E60E2952EC0986B8C02@PN3PR01MB9597.INDPRD01.PROD.OUTLOOK.COM>
Date: Mon, 24 Feb 2025 15:39:56 +0000
From: Aditya Garg <gargaditya08@...e.com>
To: "andriy.shevchenko@...ux.intel.com" <andriy.shevchenko@...ux.intel.com>
CC: "maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>,
	"mripard@...nel.org" <mripard@...nel.org>, "tzimmermann@...e.de"
	<tzimmermann@...e.de>, "airlied@...il.com" <airlied@...il.com>,
	"simona@...ll.ch" <simona@...ll.ch>, Kerem Karabay <kekrby@...il.com>,
	Atharva Tiwari <evepolonium@...il.com>, Aun-Ali Zaidi <admin@...eit.net>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
Subject: Re: [PATCH v4 2/2] drm/tiny: add driver for Apple Touch Bars in x86
 Macs



> On 24 Feb 2025, at 9:07 PM, andriy.shevchenko@...ux.intel.com wrote:
> 
> On Mon, Feb 24, 2025 at 03:20:13PM +0000, Aditya Garg wrote:
>>>> On 24 Feb 2025, at 8:41 PM, andriy.shevchenko@...ux.intel.com wrote:
>>> On Mon, Feb 24, 2025 at 03:03:40PM +0000, Aditya Garg wrote:
>>>>>> On 24 Feb 2025, at 8:27 PM, andriy.shevchenko@...ux.intel.com wrote:
>>>>> On Mon, Feb 24, 2025 at 02:32:37PM +0000, Aditya Garg wrote:
>>>>>>> On 24 Feb 2025, at 7:30 PM, andriy.shevchenko@...ux.intel.com wrote:
>>>>>>> On Mon, Feb 24, 2025 at 01:40:20PM +0000, Aditya Garg wrote:
> 
> ...
> 
>>>>>>>> +#define __APPLETBDRM_MSG_STR4(str4) ((__le32 __force)((str4[0] << 24) | (str4[1] << 16) | (str4[2] << 8) | str4[3]))
>>>>>>> 
>>>>>>> As commented previously this is quite strange what's going on with endianess in
>>>>>>> this driver. Especially the above weirdness when get_unaligned_be32() is being
>>>>>>> open coded and force-cast to __le32.
>>>>>> 
>>>>>> I would assume it was also mimicked from the Windows driver, though I haven't
>>>>>> really tried exploring this there.
>>>>>> 
>>>>>> I’d rather be happy if you give me code change suggestions and let me review
>>>>>> and test them
>>>>> 
>>>>> For the starter I would do the following for all related constants and
>>>>> drop that weird and ugly macros at the top (it also has an issue with
>>>>> the str4 length as it is 5 bytes long, not 4, btw):
>>>>> 
>>>>> #define APPLETBDRM_MSG_CLEAR_DISPLAY cpu_to_le32(0x434c5244) /* CLRD */
>>>> 
>>>> Lemme test this.
>>> 
>>> Just in case it won't work, reverse bytes in the integer. Because I was lost in
>>> this conversion.
>> 
>> It works. What I understand is that you used the macro to get the final hex
>> and converted it into little endian, which on the x86 macs would technically
>> remain the same.
> 

The Macro is just converting the letters into their hex form, but simply calculating them and putting the letters in comments is equally good.

> Right, the problem is the macro itself which does really weird things altogether.
> Using integer + comment much clearer in my opinion.
> 
>>>>> (assuming we stick with __leXX for now). This will be much less confusing.
> 
> --
> With Best Regards,
> Andy Shevchenko
> 
>