Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S945272AbcJaRxF (ORCPT ); Mon, 31 Oct 2016 13:53:05 -0400 Received: from userp1040.oracle.com ([156.151.31.81]:24993 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S938549AbcJaRxC (ORCPT ); Mon, 31 Oct 2016 13:53:02 -0400 Date: Mon, 31 Oct 2016 13:52:52 -0400 From: Konrad Rzeszutek Wilk To: Geert Uytterhoeven Cc: Jonathan Corbet , Magnus Damm , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, iommu@lists.linux-foundation.org, linux-renesas-soc@vger.kernel.org Subject: Re: [PATCH 2/2] swiotlb: Add swiotlb=nobounce debug option Message-ID: <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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1477928704-10611-3-git-send-email-geert+renesas@glider.be> User-Agent: Mutt/1.6.2 (2016-07-01) X-Source-IP: aserv0022.oracle.com [141.146.126.234] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3548 Lines: 104 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 */ } > > Note that io_tlb_nslabs is set to 1, which is the minimal supported > value. > > Signed-off-by: Geert Uytterhoeven > --- > Documentation/kernel-parameters.txt | 3 ++- > lib/swiotlb.c | 19 +++++++++++++++++-- > 2 files changed, 19 insertions(+), 3 deletions(-) > > diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt > index 37babf91f2cb6de2..38556cdceabaf087 100644 > --- a/Documentation/kernel-parameters.txt > +++ b/Documentation/kernel-parameters.txt > @@ -3998,10 +3998,11 @@ bytes respectively. Such letter suffixes can also be entirely omitted. > it if 0 is given (See Documentation/cgroup-v1/memory.txt) > > swiotlb= [ARM,IA-64,PPC,MIPS,X86] > - Format: { | force } > + Format: { | force | nobounce } > -- Number of I/O TLB slabs > force -- force using of bounce buffers even if they > wouldn't be automatically used by the kernel > + nobounce -- Never use bounce buffers (for debugging) > > switches= [HW,M68k] > > diff --git a/lib/swiotlb.c b/lib/swiotlb.c > index 6ce764410ae475cc..4550e6b516c2a4c0 100644 > --- a/lib/swiotlb.c > +++ b/lib/swiotlb.c > @@ -54,6 +54,7 @@ > #define IO_TLB_MIN_SLABS ((1<<20) >> IO_TLB_SHIFT) > > int swiotlb_force; > +static int swiotlb_nobounce; > > /* > * Used to do a quick range check in swiotlb_tbl_unmap_single and > @@ -106,8 +107,12 @@ > } > if (*str == ',') > ++str; > - if (!strcmp(str, "force")) > + if (!strcmp(str, "force")) { > swiotlb_force = 1; > + } else if (!strcmp(str, "nobounce")) { > + swiotlb_nobounce = 1; > + io_tlb_nslabs = 1; > + } > > return 0; > } > @@ -541,8 +546,15 @@ phys_addr_t swiotlb_tbl_map_single(struct device *hwdev, > map_single(struct device *hwdev, phys_addr_t phys, size_t size, > enum dma_data_direction dir) > { > - dma_addr_t start_dma_addr = phys_to_dma(hwdev, io_tlb_start); > + dma_addr_t start_dma_addr; > + > + if (swiotlb_nobounce) { > + dev_warn_ratelimited(hwdev, "Cannot do DMA to address %pa\n", > + &phys); > + return SWIOTLB_MAP_ERROR; > + } > > + start_dma_addr = phys_to_dma(hwdev, io_tlb_start); > return swiotlb_tbl_map_single(hwdev, start_dma_addr, phys, size, dir); > } > > @@ -707,6 +719,9 @@ void swiotlb_tbl_sync_single(struct device *hwdev, phys_addr_t tlb_addr, > swiotlb_full(struct device *dev, size_t size, enum dma_data_direction dir, > int do_panic) > { > + if (swiotlb_nobounce) > + return; > + > /* > * Ran out of IOMMU space for this operation. This is very bad. > * Unfortunately the drivers cannot handle this operation properly. > -- > 1.9.1 >