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=-5.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 D65C2C43382 for ; Thu, 27 Sep 2018 15:32:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 57ED3216E3 for ; Thu, 27 Sep 2018 15:32:55 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 57ED3216E3 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 S1728158AbeI0Vvl (ORCPT ); Thu, 27 Sep 2018 17:51:41 -0400 Received: from verein.lst.de ([213.95.11.211]:45948 "EHLO newverein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727262AbeI0Vvl (ORCPT ); Thu, 27 Sep 2018 17:51:41 -0400 Received: by newverein.lst.de (Postfix, from userid 2407) id 8B80768B02; Thu, 27 Sep 2018 17:32:52 +0200 (CEST) Date: Thu, 27 Sep 2018 17:32:52 +0200 From: Christoph Hellwig To: Robin Murphy Cc: Christoph Hellwig , iommu@lists.linux-foundation.org, Marek Szyprowski , Benjamin Herrenschmidt , Greg Kroah-Hartman , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH 4/5] dma-direct: implement complete bus_dma_mask handling Message-ID: <20180927153252.GE10566@lst.de> References: <20180920185247.20037-1-hch@lst.de> <20180920185247.20037-5-hch@lst.de> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.17 (2007-11-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 27, 2018 at 03:58:04PM +0100, Robin Murphy wrote: >> } >> #endif /* !CONFIG_ARCH_HAS_PHYS_TO_DMA */ >> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c >> index 3c404e33d946..64466b7ef67b 100644 >> --- a/kernel/dma/direct.c >> +++ b/kernel/dma/direct.c >> @@ -43,10 +43,11 @@ check_addr(struct device *dev, dma_addr_t dma_addr, size_t size, >> return false; >> } >> - if (*dev->dma_mask >= DMA_BIT_MASK(32)) { >> + if (*dev->dma_mask >= DMA_BIT_MASK(32) || dev->bus_dma_mask) { > > Hmm... say *dev->dma_mask is 31 bits and dev->bus_dma_mask is 40 bits due > to a global DT property, we'll now scream where we didn't before even > though the bus mask is almost certainly irrelevant - is that desirable? This is just the reporting in the error case - we'll only hit this IFF dma_capable already returned false. But if you don't want a message here we can probably drop this hunk. >> @@ -65,12 +66,18 @@ u64 dma_direct_get_required_mask(struct device *dev) >> { >> u64 max_dma = phys_to_dma_direct(dev, (max_pfn - 1) << PAGE_SHIFT); >> + if (dev->bus_dma_mask && dev->bus_dma_mask < max_dma) >> + max_dma = dev->bus_dma_mask; > > Again, I think we could just do another min_not_zero() here. A device wired > to address only one single page of RAM isn't a realistic prospect (and we > could just flip the -1 and the shift in the max_dma calculation if we > *really* wanted to support such things). This just seemed more readable to me than min_not_zero, but if others prefer min_not_zero I can switch.