linux-kernel - Re: [PATCH] usb: gadget: f_uac1: Convert use of __constant_cpu_to_le16 to cpu_to

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Date:	Mon, 5 Oct 2015 18:29:26 -0500
From:	Felipe Balbi <balbi@...com>
To:	Vaishali Thakkar <vthakkar1994@...il.com>,
	David Laight <David.Laight@...lab.com>
CC:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: gadget: f_uac1: Convert use of __constant_cpu_to_le16 to cpu_to_le16

Vaishali Thakkar <vthakkar1994@...il.com> writes:

> On Mon, Aug 24, 2015 at 2:29 PM, David Laight <David.Laight@...lab.com> wrote:
>> From: Vaishali Thakkar [mailto:vthakkar1994@...il.com]
>>> Sent: 22 August 2015 02:57
>> ...
>>> >> -     .bcdADC =               __constant_cpu_to_le16(0x0100),
>>> >> -     .wTotalLength =         __constant_cpu_to_le16(UAC_DT_TOTAL_LENGTH),
>>> >> +     .bcdADC =               cpu_to_le16(0x0100),
>>> >> +     .wTotalLength =         cpu_to_le16(UAC_DT_TOTAL_LENGTH),
>>> >
>>> > Have you test compiled this on a big-endian system?
>>> > My gut feeling is that is fails.
>>>
>>> No. I have tested it on little-endian system only. But I'll
>>> be really surprised if this will fail. Can you please tell me
>>> if I am missing something in this particular case or same
>>> applies for other cases because most of the cases like
>>> __constant_<foo> are already converted to <foo>?
>>>
>>> As far as I know, if the argument is a constant the
>>> conversion happens at compile time. And unfolding both
>>> definitions returns to same expression. Still I am trying if
>>> someone can test it for me on big endian system.
>>
>> Flip one to cpu_to_be16() and see if it still compiles.
>
> Yes. It still compiles.

it's unclear to me if this is really safe to apply. Until then I'm
dropping this from queue. Seems like, at a minimum, we need a better
commit log

-- 
balbi

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