linux-kernel - Re: [PATCH v5 2/2] arch/x86: remove pci uart early console from early

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Message-ID: <20150603030956.GB119305@worksta>
Date:	Tue, 2 Jun 2015 20:09:56 -0700
From:	Bin Gao <bin.gao@...ux.intel.com>
To:	"Anderson, Stuart R" <stuart.r.anderson@...el.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>, Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	One Thousand Gnomes <gnomes@...rguk.ukuu.org.uk>,
	Peter Hurley <peter@...leysoftware.com>,
	Jiri Slaby <jslaby@...e.cz>, Borislav Petkov <bp@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 2/2] arch/x86: remove pci uart early console from
 early_prink.c

On Wed, Jun 03, 2015 at 12:16:36AM +0000, Anderson, Stuart R wrote:
> Bin, et al,
> 
> What we are losing here is the ability to specify a UART by its bus address
> instead of just supplying the memory or io address. There are some cases
> where this is useful, though I admit it is probably not going to be widely
> used. I have seen a platform where the location of the UART moves depending
> on the firmware version, but the bus address (B:D.F) did not change. There
> are also some platforms where you do not know the address until you boot the
> OS and can use the UART to login and find the address of the UART (oops.
> Chicken and egg problem).
> 
> Also, I was going to soon send a patch to allow "pciserial32" for the case where the UART registers are 32-bit aligned instead of 8-bit aligned.
> 
> Stuart
> 

Theare are several reasons that we want to move it to serial_core.
First, pci is arch independent, so putting these codes in serial_core
(which is arch independent) makes more sense.
Second, B:D.F may change across SoCs, then to support new SoC we only
need change command line but don't need to change the code.
Lastly, there could be other non-x86 platforms using it in the future.

-Bin
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