linux-kernel - Re: [PATCH 01/11] irqchip: Allow irq_reg_{readl,writel} to use __raw_{readl

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <3403771.J3X9ZBogqZ@wuerfel>
Date:	Wed, 29 Oct 2014 22:41:03 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	Kevin Cernekee <cernekee@...il.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jason Cooper <jason@...edaemon.net>,
	Ralf Baechle <ralf@...ux-mips.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Maxime Bizon <mbizon@...ebox.fr>,
	Jonas Gorski <jogo@...nwrt.org>,
	Linux MIPS Mailing List <linux-mips@...ux-mips.org>
Subject: Re: [PATCH 01/11] irqchip: Allow irq_reg_{readl,writel} to use __raw_{readl_writel}

On Wednesday 29 October 2014 22:31:06 Thomas Gleixner wrote:
> On Wed, 29 Oct 2014, Arnd Bergmann wrote:
> > On Wednesday 29 October 2014 13:09:47 Kevin Cernekee wrote:
> > > generic-chip.c already has a fair amount of indirection, with pointers
> > > to saved masks, user-specified register offsets, and such.  Is there a
> > > concern that introducing, say, a pair of readl/writel function
> > > pointers, would cause an unacceptable performance drop?
> > 
> > I don't know. Thomas' reply suggests that it isn't. Doing byteswap
> > in software at a register access is usually free in terms of CPU
> > cycles, but an indirect function call can be noticeable if we do
> > that a lot.
> 
> I did not say that it is free. I merily said that I prefer to have
> this solved at the core level rather than at the driver level.

Yes, I understood that.

> So you have several options to do so:
> 
> 1) Indirections
> 
> 2) Different functions for the different access modes
> 
> 3) Alternatives
> 
> #1 Is the simplest solution, but imposes the overhead of an indirect
>    function call for something trivial
> 
> #2 The most efficient and flexible way if you have to provide
>    different access modes for different drivers. But it comes with the
>    price of increasing the text foot print.
> 
> #3 Smart and efficient, but requires that on a particular system all
>    drivers use the same access mode.

Right. The option that I was explaining earlier basically combines #1 and
#3: For all kernels on which we know the endianess of all generic-irqchip
users at compile time, we hardcode that, and we use indirections of
some sort for the cases where we build a kernel that needs both.

	Arnd
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/