From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1753106AbcHOMj6 (ORCPT <rfc822;w@1wt.eu>);
	Mon, 15 Aug 2016 08:39:58 -0400
Received: from pandora.armlinux.org.uk ([78.32.30.218]:57449 "EHLO
	pandora.armlinux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1752850AbcHOMj4 (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Mon, 15 Aug 2016 08:39:56 -0400
Date: Mon, 15 Aug 2016 13:39:34 +0100
From: Russell King - ARM Linux <linux@armlinux.org.uk>
To: Aleksey Makarov <aleksey.makarov@linaro.org>
Cc: "Rafael J . Wysocki" <rjw@rjwysocki.net>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        linux-serial@vger.kernel.org, linux-acpi@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        Len Brown <lenb@kernel.org>, Leif Lindholm <leif.lindholm@linaro.org>,
        Graeme Gregory <graeme.gregory@linaro.org>, Al Stone <ahs3@redhat.com>,
        Christopher Covington <cov@codeaurora.org>,
        Yury Norov <ynorov@caviumnetworks.com>,
        Peter Hurley <peter@hurleysoftware.com>,
        Andy Shevchenko <andy.shevchenko@gmail.com>,
        "Zheng, Lv" <lv.zheng@intel.com>, Mark Salter <msalter@redhat.com>,
        Kefeng Wang <wangkefeng.wang@huawei.com>, Jiri Slaby <jslaby@suse.com>
Subject: Re: [PATCH v9 4/4] serial: pl011: add console matching function
Message-ID: <20160815123934.GJ1041@n2100.armlinux.org.uk>
References: <20160811153152.755-1-aleksey.makarov@linaro.org>
 <20160811153152.755-5-aleksey.makarov@linaro.org>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20160811153152.755-5-aleksey.makarov@linaro.org>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Thu, Aug 11, 2016 at 06:31:41PM +0300, Aleksey Makarov wrote:
> +/**
> + *	pl011_console_match - non-standard console matching
> + *	@co:	  registering console
> + *	@name:	  name from console command line
> + *	@idx:	  index from console command line
> + *	@options: ptr to option string from console command line
> + *
> + *	Only attempts to match console command lines of the form:
> + *	    console=pl011,mmio|mmio32,<addr>[,<options>]
> + *	    console=pl011,0x<addr>[,<options>]
> + *	This form is used to register an initial earlycon boot console and
> + *	replace it with the amba_console at pl011 driver init.
> + *
> + *	Performs console setup for a match (as required by interface)
> + *	If no <options> are specified, then assume the h/w is already setup.
> + *
> + *	Returns 0 if console matches; otherwise non-zero to use default matching
> + */
> +static int __init pl011_console_match(struct console *co, char *name, int idx,
> +				      char *options)
> +{
> +	char match[] = "pl011";	/* pl011-specific earlycon name */

This is inefficient - the compiler will probably store "pl011" in the
rodata section, then allocate an array on the stack, and them memcpy()
it onto the stack.  This is really a false optimisation.

> +	unsigned char iotype;
> +	unsigned long addr;
> +	int i;
> +
> +	if (strncmp(name, match, 5) != 0)

Just do:

	if (strncmp(name, "pl011", 5) != 0)

here, and let the compiler work it out - it'll probably place "pl011"
in the rodata section, and use a pointer to it rather than messing around
with the stack.

What if "console=pl011x,..." is passed?  Should this be matched too?
Maybe this should compare with "pl011," to ensure that the name is
correctly terminated?

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.