From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757733AbYKESjQ (ORCPT ); Wed, 5 Nov 2008 13:39:16 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757307AbYKESg6 (ORCPT ); Wed, 5 Nov 2008 13:36:58 -0500 Received: from rv-out-0506.google.com ([209.85.198.229]:17653 "EHLO rv-out-0506.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753320AbYKESg5 (ORCPT ); Wed, 5 Nov 2008 13:36:57 -0500 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references; b=lhMXAzKbCPhlxv7U3vDmJV4CxINQHkaWMZ5HoLCy76eMemmyQZ8v9GJSwicK03NnEb YzasMjNeNjtfcw6HnTpxoGvofIa7nUoFu7diQtdjH7mROj7hTTQxXS1szOLpFLnIyqe7 XGh09AA6Bd8bBeQYL2Xd88v0svl6MWDvussaY= Message-ID: <8bd0f97a0811051036w32717036k337f3ce1b3194198@mail.gmail.com> Date: Wed, 5 Nov 2008 13:36:56 -0500 From: "Mike Frysinger" To: "Hans J. Koch" Subject: Re: [PATCH] UIO: only call pgprot_noncached if defined Cc: "Greg KH" , "Mike Frysinger" , linux-kernel@vger.kernel.org In-Reply-To: <20081105182743.GE6382@local> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <1225301177-21406-1-git-send-email-vapier@gentoo.org> <20081105113610.GA6382@local> <20081105163334.GA8473@suse.de> <8bd0f97a0811050933m13addb7eiddb963bfdf4d7416@mail.gmail.com> <20081105182743.GE6382@local> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 5, 2008 at 13:27, Hans J. Koch wrote: > On Wed, Nov 05, 2008 at 12:33:37PM -0500, Mike Frysinger wrote: >> On Wed, Nov 5, 2008 at 11:33, Greg KH wrote: >> > On Wed, Nov 05, 2008 at 12:36:11PM +0100, Hans J. Koch wrote: >> >> There seem to be archs that cannot easily implement a sensible >> >> pgprot_noncached() function, so we should merge this patch. UIO doesn't >> >> compile on these archs right now. >> > >> > No, we should fix those arches to have that function at least NULLed >> > out. Isn't there only one, Blackfin? Putting #ifdefs in .c files is >> > not something we really want to do if at all possible. >> >> that was my question. this function isnt documented. if the hardware >> doesnt support it, is the right thing really for the arch to lie to >> drivers and not actually give back cached settings even though it >> asked for non-cached ? > > Well, if there's no possibility to map device memory in a non-cached > way, it's very likely you don't want to use UIO at all. If there's a few > seconds between a write and the value actually appearing in the hardware > register, you will certainly don't see the results you expect. > > If Blackfin can't mmap non-cached memory, we should make UIO depend on > !BLACKFIN. if it wasnt usable on the Blackfin arch, i wouldnt have been looking at it in the first place. there is some usage where merely hooking up an interrupt is the only thing that is needed by userspace. the only memory regions where a device would be hooked up are never marked as cachable. so if this function is only for mapping addresses where device registers would live, then a stub pgprot_noncached() would be fine. but we cant do non-cached access on external memory (e.g. SDRAM / DDR) if the device wanted coherent memory for dma. -mike