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=-8.6 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT 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 CCA27C43143 for ; Mon, 1 Oct 2018 20:11:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 93ECF2084C for ; Mon, 1 Oct 2018 20:11:22 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="fVooRxjF" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 93ECF2084C Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=lst.de 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 S1726455AbeJBCtv (ORCPT ); Mon, 1 Oct 2018 22:49:51 -0400 Received: from bombadil.infradead.org ([198.137.202.133]:48842 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725936AbeJBCtv (ORCPT ); Mon, 1 Oct 2018 22:49:51 -0400 DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=bombadil.20170209; h=Content-Transfer-Encoding: MIME-Version:References:In-Reply-To:Message-Id:Date:Subject:Cc:To:From:Sender :Reply-To:Content-Type:Content-ID:Content-Description:Resent-Date:Resent-From :Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id:List-Help: List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=gpJfkgtynyfTzWqSnZxf/m8M5D38vsOcfAqFCE1AVv0=; b=fVooRxjFVYe9SIWj59n1v6EkGt dSratgcbvm+1AHtGl9Q3K8WKmYCt/4VMo2Xrl0g7hiMD38+3ojNLwSImKxSd/VsqGE+FNNrSFBnUh xZ6vZUrSMIaL2Suv26gHI7O1AGkIqPeWWB4hJQYjKAKwTkRiW2xxIG6USMVjXOyNEnS0P+DxC/NZD i0DOHnp1MnTki678Z1YMZK0dM1boyVI293MthfoPnb11S5IaD/e7w3DqnQ99gmo6+TzqQoJJhncSI pAwNxymNMHdjVyslpWozKU0g7k8M4xanfm6yWTETy1ydXpG1bhhWtXXLz9hodBkUK5PsyRDR+7w3G 4Yfb0Mpg==; Received: from [38.126.112.138] (helo=localhost) by bombadil.infradead.org with esmtpsa (Exim 4.90_1 #2 (Red Hat Linux)) id 1g74WI-0006Zo-GR; Mon, 01 Oct 2018 20:10:18 +0000 From: Christoph Hellwig To: iommu@lists.linux-foundation.org Cc: Marek Szyprowski , Robin Murphy , Benjamin Herrenschmidt , linux-kernel@vger.kernel.org Subject: [PATCH] dma-direct: document the zone selection logic Date: Mon, 1 Oct 2018 13:10:16 -0700 Message-Id: <20181001201016.32639-2-hch@lst.de> X-Mailer: git-send-email 2.19.0 In-Reply-To: <20181001201016.32639-1-hch@lst.de> References: <20181001201016.32639-1-hch@lst.de> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-SRS-Rewrite: SMTP reverse-path rewritten from by bombadil.infradead.org. See http://www.infradead.org/rpr.html Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org What we are doing here isn't quite obvious, so add a comment explaining it. Signed-off-by: Christoph Hellwig --- kernel/dma/direct.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c index ba6f5956a291..14b966e2349a 100644 --- a/kernel/dma/direct.c +++ b/kernel/dma/direct.c @@ -84,7 +84,14 @@ static gfp_t __dma_direct_optimal_gfp_mask(struct device *dev, u64 dma_mask, else *phys_mask = dma_to_phys(dev, dma_mask); - /* GFP_DMA32 and GFP_DMA are no ops without the corresponding zones: */ + /* + * Optimistically try the zone that the physicall address mask falls + * into first. If that returns memory that isn't actually addressable + * we will fallback to the next lower zone and try again. + * + * Note that GFP_DMA32 and GFP_DMA are no ops without the corresponding + * zones. + */ if (*phys_mask <= DMA_BIT_MASK(ARCH_ZONE_DMA_BITS)) return GFP_DMA; if (*phys_mask <= DMA_BIT_MASK(32)) -- 2.19.0