linux-kernel - Re: [PATCH v2 5/5] tty/serial: Add earlycon support for Spreadtrum serial driver

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Message-ID: <CA+H2tpGJuukXZuGwysa5Y6LvjgZj3TVDWfngpM67p3nfzdi0YQ@mail.gmail.com>
Date:	Tue, 21 Oct 2014 21:34:41 +0800
From:	Orson Zhai <orsonzhai@...il.com>
To:	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>
Cc:	Chunyan Zhang <chunyan.zhang@...eadtrum.com>,
	Catalin Marinas <catalin.marinas@....com>,
	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"jslaby@...e.cz" <jslaby@...e.cz>,
	Kumar Gala <galak@...eaurora.org>,
	Mark Brown <broonie@...aro.org>,
	Mark Rutland <mark.rutland@....com>,
	"m-karicheri2@...com" <m-karicheri2@...com>,
	Pawel Moll <pawel.moll@....com>,
	Ramkumar Ramachandra <artagnon@...il.com>,
	"rrichter@...ium.com" <rrichter@...ium.com>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	Will Deacon <will.deacon@....com>,
	Geng Ren ( 任赓) <geng.ren@...eadtrum.com>,
	Zhizhou Zhang ( 张治洲) 
	<zhizhou.zhang@...eadtrum.com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	sprdlinux <sprdlinux@...elists.org>
Subject: Re: [PATCH v2 5/5] tty/serial: Add earlycon support for Spreadtrum
 serial driver

On Tue, Oct 21, 2014 at 8:26 PM, One Thousand Gnomes
<gnomes@...rguk.ukuu.org.uk> wrote:
> On Mon, 20 Oct 2014 18:23:38 +0800
> Orson Zhai <orsonzhai@...il.com> wrote:
>
>> On Sun, Oct 19, 2014 at 5:06 AM, One Thousand Gnomes
>> <gnomes@...rguk.ukuu.org.uk> wrote:
>> > On Fri, 17 Oct 2014 17:54:25 +0800
>> > Chunyan Zhang <chunyan.zhang@...eadtrum.com> wrote:
>> >
>> >> Add serial driver for spreadtrum sharkl platform with earlycon
>> >> support at first.
>> >
>> >> +#define UART_TXD     0x0000
>> >> +#define UART_RXD     0x0004
>> >> +#define UART_STS0    0x0008
>> >> +#define UART_STS1    0x000C
>> >> +#define UART_IEN     0x0010
>> >> +#define UART_ICLR    0x0014
>> >> +#define UART_CTL0    0x0018
>> >> +#define UART_CTL1    0x001C
>> >> +#define UART_CTL2    0x0020
>> >> +#define UART_CLKD0   0x0024
>> >> +#define UART_CLKD1   0x0028
>> >> +#define UART_STS2    0x002C
>> >> +
>> >> +/*line status */
>> >> +#define UART_LSR_TX_OVER     (0x1<<15)
>> >
>> > Given we use UART_ for all the 8250 defines it might be better to use
>> > something else - SHARK_LSR_TX_OVER etc to avoid future confusion
>> >
>>
>> Does it matter if those macro are only used in the specific c file?
>> >From my point of  view, private register macro could be treated as
>> static definitions like static variable or functions in C file.
>> I also noted that many people use a prefix for the other
>> manufacturers' macro definition in source file .
>> I have no intention to break the habit of kernel but just for discussion.
>
> Your problem is this. In the kernel headers are definitions like
>
> include/uapi/linux/serial_reg.h:#define UART_TX 0       /* Out: Transmit
> buffer */
>
> you are adding identical (but conflicting in places) defines. If some
> random change in the include files causes serial_reg.h to be included by
> a header you include then it will break.
>
> In addition people habitually use tools like LXR to figure out where
> defines and functions are.

This make much more sense, thanks for you explanation.

> Having these conflicting definitions will
> cause confusion. Better they have prefixes.
>
> Alan
>
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