Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751173AbaDQS14 (ORCPT ); Thu, 17 Apr 2014 14:27:56 -0400 Received: from mail-vc0-f182.google.com ([209.85.220.182]:58245 "EHLO mail-vc0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750998AbaDQS1r (ORCPT ); Thu, 17 Apr 2014 14:27:47 -0400 MIME-Version: 1.0 In-Reply-To: <21117957.8m9iUdR1VN@wuerfel> References: <1395436128-11244-1-git-send-email-robherring2@gmail.com> <9368307.RXEGmQia1C@wuerfel> <21117957.8m9iUdR1VN@wuerfel> Date: Thu, 17 Apr 2014 13:27:46 -0500 Message-ID: Subject: Re: [PATCH 4/8] tty/serial: add generic serial earlycon From: Rob Herring To: Arnd Bergmann , Alan Cox Cc: "linux-arm-kernel@lists.infradead.org" , Catalin Marinas , Russell King , Greg Kroah-Hartman , "x86@kernel.org" , Will Deacon , "linux-kernel@vger.kernel.org" , "linux-serial@vger.kernel.org" , Jiri Slaby Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 24, 2014 at 10:42 AM, Arnd Bergmann wrote: > On Monday 24 March 2014 08:36:46 Rob Herring wrote: >> On Mon, Mar 24, 2014 at 6:29 AM, Arnd Bergmann wrote: >> > On Monday 24 March 2014 11:22:03 Catalin Marinas wrote: >> >> On Fri, Mar 21, 2014 at 09:08:44PM +0000, Rob Herring wrote: >> >> > diff --git a/drivers/tty/serial/earlycon.c b/drivers/tty/serial/earlycon.c >> >> > new file mode 100644 >> >> > index 0000000..241757a >> >> > --- /dev/null >> >> > +++ b/drivers/tty/serial/earlycon.c >> >> [...] >> >> > +static void __iomem * __init earlycon_map(unsigned long paddr, size_t size) >> >> > +{ >> >> > + void __iomem *base; >> >> > +#ifdef CONFIG_FIX_EARLYCON_MEM >> >> > + set_fixmap_nocache(FIX_EARLYCON_MEM_BASE, paddr & PAGE_MASK); >> >> > + base = (void __iomem *)__fix_to_virt(FIX_EARLYCON_MEM_BASE); >> >> > + base += paddr & ~PAGE_MASK; >> >> > +#else >> >> > + base = ioremap_nocache(paddr, size); >> >> > +#endif >> >> >> >> Just curious why not set_fixmap_io (and plain ioremap)? >> > >> > Good point. Note that ioremap_nocache() is the same as ioremap() >> > on *all* architectures. Did you mean "not the same"? Why are there 2 flavors if they are always the same. >> I investigated this before adding this to arm64. set_fixmap_io and >> set_fixmap_nocache are not the same settings on x86. Whether the >> mapping type really matters on x86 or not, I don't know. So I added >> the nocache variant to arm64 to avoid a change to x86. > > My best guess is that it's an x86 bug. ioremap() always uses an uncached > mapping on x86, so it's strange to see early_ioremap() and set_fixmap_io() > use a cached mapping. It probably doesn't matter as long as the mtrr is > set up to treat all MMIO registers as non-cacheable, but I think there > should not be a difference. At some point it was believed to be needed on the 8250 driver. Perhaps Alan can comment since the commit message tells us nothing: commit 6f441fe99814f64315b8c11890744230b990c460 Author: Alan Cox Date: Thu May 1 04:34:59 2008 -0700 8250: switch 8250 drivers to use _nocache ioremaps Signed-off-by: Alan Cox Cc: Russell King Cc: Ingo Molnar Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Rob -- 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/