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 S932147AbcBZKln (ORCPT <rfc822;w@1wt.eu>);
	Fri, 26 Feb 2016 05:41:43 -0500
Received: from mail-ig0-f178.google.com ([209.85.213.178]:33660 "EHLO
	mail-ig0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1754251AbcBZKlk convert rfc822-to-8bit (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Fri, 26 Feb 2016 05:41:40 -0500
MIME-Version: 1.0
In-Reply-To: <alpine.DEB.2.00.1601240345260.5958@tp.orcam.me.uk>
References: <1452991370-20121-1-git-send-email-zajec5@gmail.com>
	<alpine.DEB.2.00.1601240345260.5958@tp.orcam.me.uk>
Date: Fri, 26 Feb 2016 11:41:39 +0100
Message-ID: <CACna6rzBTKXE6=ej-PY7V3facAR9kJ-Tq2LDc2EwszaTCK+2YA@mail.gmail.com>
Subject: Re: [PATCH] mtd: bcm47xxsflash: use ioremap_cachable() instead of KSEG0ADDR()
From: =?UTF-8?B?UmFmYcWCIE1pxYJlY2tp?= <zajec5@gmail.com>
To: "Maciej W. Rozycki" <macro@imgtec.com>
Cc: Brian Norris <computersforpeace@gmail.com>,
        "linux-mtd@lists.infradead.org" <linux-mtd@lists.infradead.org>,
        Javier Martinez Canillas <javier@osg.samsung.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Fengguang Wu <fengguang.wu@intel.com>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Luis de Bethencourt <luisbg@osg.samsung.com>,
        Jeremy Kerr <jk@ozlabs.org>,
        Neelesh Gupta <neelegup@linux.vnet.ibm.com>,
        David Woodhouse <dwmw2@infradead.org>, Cyril Bur <cyrilbur@gmail.com>,
        Ralf Baechle <ralf@linux-mips.org>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8BIT
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 24 January 2016 at 21:17, Maciej W. Rozycki <macro@imgtec.com> wrote:
> On Sun, 17 Jan 2016, Rafał Miłecki wrote:
>
>> KSEG0ADDR was translating 0x1c000000 into 0x9c000000. With
>> ioremap_cachable we use MIPS's __ioremap (and remap_area_pages). This
>> results in different address (e.g. 0xc0080000) but it still should be
>> cached as expected and it was successfully tested with BCM47186B0.
>
>  This is due to this piece:
>
>         /*
>          * Map uncached objects in the low 512mb of address space using KSEG1,
>          * otherwise map using page tables.
>          */
>         if (IS_LOW512(phys_addr) && IS_LOW512(last_addr) &&
>             flags == _CACHE_UNCACHED)
>                 return (void __iomem *) CKSEG1ADDR(phys_addr);
>
> special-casing uncached mapping only (replicated in 2 places).  I think
> there will really be no harm from returning a KSEG0 mapping for calls
> requesting a caching mode equal to `_page_cachable_default', which --
> depending on the cache architecture -- will have been either hardwired or
> prearranged via Config.K0.  I think there's really no need to put pressure
> on the TLB, which may be small, in cases where a fixed mapping will do.

No, it isn't hitting condition you pointed. We call ioremap_cachable
which uses _page_cachable_default as a flag. This flag
(_page_cachable_default) isn't equal to the _CACHE_UNCACHED.

Moreover code you pointed uses CKSEG1ADDR which would result in
setting bit KSEG1 (0xa0000000). As I pointed in the commit message
address it ORed with KSEG2 (0xc0000000).

So what really happens is what my commit message says:
ioremap_cachable -> __ioremap -> remap_area_pages