From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 8451CC43382 for ; Thu, 27 Sep 2018 01:50:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2A8142156D for ; Thu, 27 Sep 2018 01:50:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2A8142156D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.crashing.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727204AbeI0IGZ (ORCPT ); Thu, 27 Sep 2018 04:06:25 -0400 Received: from gate.crashing.org ([63.228.1.57]:33193 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726477AbeI0IGZ (ORCPT ); Thu, 27 Sep 2018 04:06:25 -0400 Received: from localhost (localhost.localdomain [127.0.0.1]) by gate.crashing.org (8.14.1/8.14.1) with ESMTP id w8R1oEgP008244; Wed, 26 Sep 2018 20:50:15 -0500 Message-ID: <985079efc3296ac45de1e6344d7916c42fc7cbdd.camel@kernel.crashing.org> Subject: Re: [PATCH 5/5] dma-direct: always allow dma mask <= physiscal memory size From: Benjamin Herrenschmidt To: Christoph Hellwig , iommu@lists.linux-foundation.org Cc: Marek Szyprowski , Robin Murphy , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Date: Thu, 27 Sep 2018 11:50:14 +1000 In-Reply-To: <20180920185247.20037-6-hch@lst.de> References: <20180920185247.20037-1-hch@lst.de> <20180920185247.20037-6-hch@lst.de> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.28.5 (3.28.5-1.fc28) Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 2018-09-20 at 20:52 +0200, Christoph Hellwig wrote: > This way an architecture with less than 4G of RAM can support dma_mask > smaller than 32-bit without a ZONE_DMA. Apparently that is a common > case on powerpc. Anything that uses a b43 wifi adapter which has a 31-bit limitation actually :-) > > Signed-off-by: Christoph Hellwig > --- > kernel/dma/direct.c | 28 ++++++++++++++++------------ > 1 file changed, 16 insertions(+), 12 deletions(-) > > diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c > index 64466b7ef67b..d1e103c6b107 100644 > --- a/kernel/dma/direct.c > +++ b/kernel/dma/direct.c > @@ -4,6 +4,7 @@ > * > * DMA operations that map physical memory directly without using an IOMMU. > */ > +#include /* for max_pfn */ > #include > #include > #include > @@ -283,21 +284,24 @@ int dma_direct_map_sg(struct device *dev, struct scatterlist *sgl, int nents, > return nents; > } > > +/* > + * Because 32-bit DMA masks are so common we expect every architecture to be > + * able to satisfy them - either by not supporting more physical memory, or by > + * providing a ZONE_DMA32. If neither is the case, the architecture needs to > + * use an IOMMU instead of the direct mapping. > + */ > int dma_direct_supported(struct device *dev, u64 mask) > { > -#ifdef CONFIG_ZONE_DMA > - if (mask < phys_to_dma(dev, DMA_BIT_MASK(ARCH_ZONE_DMA_BITS))) > - return 0; > -#else > - /* > - * Because 32-bit DMA masks are so common we expect every architecture > - * to be able to satisfy them - either by not supporting more physical > - * memory, or by providing a ZONE_DMA32. If neither is the case, the > - * architecture needs to use an IOMMU instead of the direct mapping. > - */ > - if (mask < phys_to_dma(dev, DMA_BIT_MASK(32))) > + u64 min_mask; > + > + if (IS_ENABLED(CONFIG_ZONE_DMA)) > + min_mask = DMA_BIT_MASK(ARCH_ZONE_DMA_BITS); > + else > + min_mask = min_t(u64, DMA_BIT_MASK(32), > + (max_pfn - 1) << PAGE_SHIFT); > + > + if (mask >= phys_to_dma(dev, min_mask)) > return 0; nitpick ... to be completely "correct", I would have written if (IS_ENABLED(CONFIG_ZONE_DMA)) min_mask = DMA_BIT_MASK(ARCH_ZONE_DMA_BITS); else min_mask = DMA_BIT_MASK(32); min_mask = min_t(u64, min_mask, (max_pfn - 1) << PAGE_SHIFT); In "theory" it's also ok to have a mask < ZONE_DMA_BITS as long as it's big enough to fit all memory :-) > -#endif > return 1; > } >