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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no 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 1D905C433E2 for ; Thu, 3 Sep 2020 00:41:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E948620786 for ; Thu, 3 Sep 2020 00:41:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727088AbgICAlh (ORCPT ); Wed, 2 Sep 2020 20:41:37 -0400 Received: from brightrain.aerifal.cx ([216.12.86.13]:49010 "EHLO brightrain.aerifal.cx" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726312AbgICAlh (ORCPT ); Wed, 2 Sep 2020 20:41:37 -0400 Date: Wed, 2 Sep 2020 20:41:35 -0400 From: Rich Felker To: Geert Uytterhoeven Cc: Ulf Hansson , Christoph Hellwig , "linux-mmc@vger.kernel.org" , Mark Brown , Linux-sh list , Linux Kernel Mailing List Subject: Re: [PATCH v2] mmc: mmc_spi: Allow the driver to be built when CONFIG_HAS_DMA is unset Message-ID: <20200903004135.GT3265@brightrain.aerifal.cx> References: <20200901150438.228887-1-ulf.hansson@linaro.org> <20200901150654.GB30034@lst.de> <20200901154049.GA376@lst.de> <20200902134418.GR3265@brightrain.aerifal.cx> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Sep 02, 2020 at 05:51:16PM +0200, Geert Uytterhoeven wrote: > Hi Rich, > > On Wed, Sep 2, 2020 at 5:43 PM Rich Felker wrote: > > On Wed, Sep 02, 2020 at 10:31:47AM +0200, Ulf Hansson wrote: > > > On Tue, 1 Sep 2020 at 17:40, Christoph Hellwig wrote: > > > > On Tue, Sep 01, 2020 at 05:36:17PM +0200, Ulf Hansson wrote: > > > > > > I still don't think this makes sense, as the dma_mask should always > > > > > > be non-NULL here. > > > > > > > > > > If that is the case, I wonder how the driver could even have worked without DMA. > > > > > > > > > > Because in the existing code, host->dma_dev gets assigned to > > > > > spi->master->dev.parent->dma_mask - which seems to turn on the DMA > > > > > usage in the driver. > > > > > > > > > > What am I missing? > > > > > > > > Do you know of other non-DMA users? For SH nommu it probably worked > > > > > > I don't know of other non-DMA users. As I said, I wish someone could > > > step in and take better care of mmc_spi - as I know it's being used a > > > lot. > > > > > > > because SH nommu used to provide a DMA implementation that worked > > > > fine for streaming maps, but was completely broken for coherent > > > > allocation. And this driver appears to only use the former. > > > > > > Alright, so you are saying the DMA support may potentially never have > > > been optional to this driver. In any case, I can remove the check in > > > $subject patch, as it shouldn't matter. > > > > DMA support was always optional, because even on systems where DMA is > > present, it doesn't necessarily mean the SPI controller uses DMA. In > > particular, pure bit-banged SPI via GPIOs doesn't have DMA, but has > > always worked. See my previous reply to Christoph about host->dma_dev > > for my current-best understanding of what's going on here. > > > > > Anyway, let's see what Rich thinks of this. I am curious to see if the > > > patch works on his SH boards - as I haven't been able to test it. > > > > I'll rebuild and retest just to confirm, but I already tested a > > functionally equivalent patch that just did the #ifdef inline (rather > > than moving the logic out to separate functions) and it worked fine. > > Hence, Tested-by? ;-) Confirmed that this version of the patch works too. Thus, Tested-by: Rich Felker