From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH 4/8] tty/serial: add generic serial earlycon Date: Mon, 24 Mar 2014 16:42:02 +0100 Message-ID: <21117957.8m9iUdR1VN@wuerfel> References: <1395436128-11244-1-git-send-email-robherring2@gmail.com> <9368307.RXEGmQia1C@wuerfel> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: Received: from moutng.kundenserver.de ([212.227.17.24]:64070 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753220AbaCXPml (ORCPT ); Mon, 24 Mar 2014 11:42:41 -0400 In-Reply-To: Sender: linux-serial-owner@vger.kernel.org List-Id: linux-serial@vger.kernel.org To: Rob Herring 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 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. > > 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. Arnd