Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754246Ab3H1JtJ (ORCPT ); Wed, 28 Aug 2013 05:49:09 -0400 Received: from top.free-electrons.com ([176.31.233.9]:41193 "EHLO mail.free-electrons.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1752477Ab3H1JtH (ORCPT ); Wed, 28 Aug 2013 05:49:07 -0400 Date: Wed, 28 Aug 2013 06:49:08 -0300 From: Ezequiel Garcia To: Catalin Marinas Cc: "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Thomas Petazzoni , Gregory Clement , Lior Amsalem , Baruch Siach , Will Deacon , Sebastian Hesselbarth , Russell King Subject: Re: [PATCH v4 2/4] ARM: Add atomic_io_modify optimized routines Message-ID: <20130828094907.GB2343@localhost> References: <1377358532-23802-1-git-send-email-ezequiel.garcia@free-electrons.com> <1377358532-23802-3-git-send-email-ezequiel.garcia@free-electrons.com> <20130828085340.GB58219@MacBook-Pro.local> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20130828085340.GB58219@MacBook-Pro.local> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3304 Lines: 90 On Wed, Aug 28, 2013 at 09:53:40AM +0100, Catalin Marinas wrote: > On Sat, Aug 24, 2013 at 04:35:30PM +0100, Ezequiel Garcia wrote: > > Implement arch-specific atomic_io_modify and atomic_io_modify_relaxed, > > which are based on writel/readl_relaxed and writel_relaxed/readl_relaxed, > > respectively. > > In both cases, by relaxing the readl, perfomance can be improved. > > > > Signed-off-by: Ezequiel Garcia > > --- > > arch/arm/include/asm/io.h | 4 ++++ > > arch/arm/kernel/io.c | 29 +++++++++++++++++++++++++++++ > > 2 files changed, 33 insertions(+) > > > > diff --git a/arch/arm/include/asm/io.h b/arch/arm/include/asm/io.h > > index d070741..53637b6 100644 > > --- a/arch/arm/include/asm/io.h > > +++ b/arch/arm/include/asm/io.h > > @@ -397,5 +397,9 @@ extern int devmem_is_allowed(unsigned long pfn); > > extern void register_isa_ports(unsigned int mmio, unsigned int io, > > unsigned int io_shift); > > > > +#define __HAVE_ARCH_ATOMIC_IO_MODIFY > > +extern void atomic_io_modify(void __iomem *reg, u32 mask, u32 set); > > +extern void atomic_io_modify_relaxed(void __iomem *reg, u32 mask, u32 set); > > + > > #endif /* __KERNEL__ */ > > #endif /* __ASM_ARM_IO_H */ > > diff --git a/arch/arm/kernel/io.c b/arch/arm/kernel/io.c > > index dcd5b4d..a8c9c9b 100644 > > --- a/arch/arm/kernel/io.c > > +++ b/arch/arm/kernel/io.c > > @@ -1,6 +1,35 @@ > > #include > > #include > > #include > > +#include > > + > > +static DEFINE_RAW_SPINLOCK(__io_lock); > > + > > +void atomic_io_modify_relaxed(void __iomem *reg, u32 mask, u32 set) > > +{ > > + unsigned long flags; > > + u32 value; > > + > > + raw_spin_lock_irqsave(&__io_lock, flags); > > + value = readl_relaxed(reg) & ~mask; > > + value |= (set & mask); > > + writel_relaxed(value, reg); > > + raw_spin_unlock_irqrestore(&__io_lock, flags); > > +} > > +EXPORT_SYMBOL(atomic_io_modify_relaxed); > > + > > +void atomic_io_modify(void __iomem *reg, u32 mask, u32 set) > > +{ > > + unsigned long flags; > > + u32 value; > > + > > + raw_spin_lock_irqsave(&__io_lock, flags); > > + value = readl_relaxed(reg) & ~mask; > > + value |= (set & mask); > > + writel(value, reg); > > + raw_spin_unlock_irqrestore(&__io_lock, flags); > > +} > > +EXPORT_SYMBOL(atomic_io_modify); > > Is this any different from the generic one introduced in patch 1/4? I > would rather just use the generic definition. Well, according to Will Deacon (and as documented in the commit log) we can optimize in ARM by using readl_relaxed instead of readl. Now, I'm sure you now better than me if that results (or not) in any significant optimization. > Similarly, a generic > atomic_io_modify_relaxed() but guarded with something like > __HAVE_ARCH_RELAXED_IO. > No, that's not possible. As far as I understand, there's no guarantee of _relaxed variants to be available architecture-wide. -- Ezequiel García, Free Electrons Embedded Linux, Kernel and Android Engineering http://free-electrons.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/