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=-8.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 C43D8C433E7 for ; Sat, 29 Aug 2020 08:31:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A455E2068E for ; Sat, 29 Aug 2020 08:31:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727093AbgH2Ib0 (ORCPT ); Sat, 29 Aug 2020 04:31:26 -0400 Received: from verein.lst.de ([213.95.11.211]:44101 "EHLO verein.lst.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726083AbgH2Ib0 (ORCPT ); Sat, 29 Aug 2020 04:31:26 -0400 Received: by verein.lst.de (Postfix, from userid 2407) id 0EAD668C4E; Sat, 29 Aug 2020 10:31:21 +0200 (CEST) Date: Sat, 29 Aug 2020 10:31:21 +0200 From: Christoph Hellwig To: Rich Felker Cc: Ulf Hansson , Christoph Hellwig , Yoshinori Sato , Linux-sh list , Linux Kernel Mailing List , "linux-mmc@vger.kernel.org" , linux-spi@vger.kernel.org Subject: Re: [PATCH 09/10] sh: don't allow non-coherent DMA for NOMMU Message-ID: <20200829083121.GA7851@lst.de> References: <20200714121856.955680-1-hch@lst.de> <20200714121856.955680-10-hch@lst.de> <20200828020045.GT3265@brightrain.aerifal.cx> <20200828021152.GU3265@brightrain.aerifal.cx> <20200828042422.GA29734@lst.de> <20200828150942.GV3265@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200828150942.GV3265@brightrain.aerifal.cx> 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 Fri, Aug 28, 2020 at 11:09:43AM -0400, Rich Felker wrote: > > However, by looking at the code, one get the feeling that the DMA > > support is somewhat prepared to be made optional. I guess it has never > > been really tested, as the Kconfig option has "depends on HAS_DMA" - > > and it's been like that as long as I can remember. > > It always worked on our "byte-banged" SPI controller, with no DMA > controller present, before Christoph's changes in this patch series, Before that nommu sh builds provided a DMA mapping implementation that even worked for the streaming side (dma_map_*), but would corrupt data if you used dma_alloc_coherent memory to communicate with the device. > and seems to be working now (although I have some other, hopefully > unrelated regressions to debug) with #ifdef CONFIG_HAS_DMA around the > if (spi->master->dev.parent->dma_mask) block in mmc_spi_probe. That's > probably not the right fix though -- why isn't it checking > host->dma_dev instead and only attempting DMA setup if dma_dev is > non-null? I don't think dma_dev can be NULL right now. dma_dev is assigned here: if (spi->master->dev.parent->dma_mask) { struct device *dev = spi->master->dev.parent; host->dma_dev = dev; but for any OF or real bus device dma_mask never is zero (it actually is a pointer), and the value of it also is initialized to 32-bit by default, making this effectively an "if (1) {". The driver needs some way to communicate if a given device actually is DMA capable or not. Or is that purely a factor of the platform which would be a little strange. In which case we should do something like: diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c index 39bb1e30c2d722..3b0cc9a70e6432 100644 --- a/drivers/mmc/host/mmc_spi.c +++ b/drivers/mmc/host/mmc_spi.c @@ -1374,7 +1374,7 @@ static int mmc_spi_probe(struct spi_device *spi) if (!host->data) goto fail_nobuf1; - if (spi->master->dev.parent->dma_mask) { + if (IS_ENABLED(CONFIG_HAS_DMA)) { struct device *dev = spi->master->dev.parent; host->dma_dev = dev;