Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933852AbcKGTRL (ORCPT ); Mon, 7 Nov 2016 14:17:11 -0500 Received: from mail-wm0-f67.google.com ([74.125.82.67]:34675 "EHLO mail-wm0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933184AbcKGTQ7 (ORCPT ); Mon, 7 Nov 2016 14:16:59 -0500 MIME-Version: 1.0 In-Reply-To: <20161031175252.GA6952@char.us.oracle.com> References: <1477928704-10611-1-git-send-email-geert+renesas@glider.be> <1477928704-10611-3-git-send-email-geert+renesas@glider.be> <20161031175252.GA6952@char.us.oracle.com> From: Geert Uytterhoeven Date: Mon, 7 Nov 2016 19:57:11 +0100 X-Google-Sender-Auth: SqNiB9yDpVIR68N91CmIMeApgGg Message-ID: Subject: Re: [PATCH 2/2] swiotlb: Add swiotlb=nobounce debug option To: Konrad Rzeszutek Wilk Cc: Geert Uytterhoeven , Jonathan Corbet , Magnus Damm , "linux-kernel@vger.kernel.org" , "linux-doc@vger.kernel.org" , iommu@lists.linux-foundation.org, Linux-Renesas Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1466 Lines: 38 Hi Konrad, On Mon, Oct 31, 2016 at 6:52 PM, Konrad Rzeszutek Wilk wrote: > On Mon, Oct 31, 2016 at 04:45:04PM +0100, Geert Uytterhoeven wrote: >> On architectures like arm64, swiotlb is tied intimately to the core >> architecture DMA support. In addition, ZONE_DMA cannot be disabled. >> >> To aid debugging and catch devices not supporting DMA to memory outside >> the 32-bit address space, add a kernel command line option >> "swiotlb=nobounce", which disables the use of bounce buffers. >> If specified, trying to map memory that cannot be used with DMA will >> fail, and a warning will be printed (rate-limited). > > I would make the 'swiotlb_force' an enum. And then instead of this > being 'nobounce' just do the inverse of 'force', that is the > 'noforce' would trigger this no bounce effect. > > So: > > enum { > NORMAL, /* Default - depending on the hardware DMA mask and such. */ > FORCE, /* swiotlb=force */ > NO_FORCE, /* swiotlb=noforce */ Fine for me, but swiotlb_force is exported to platform code. Hence all users should be updated? Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds