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=-4.0 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 A6B8CC433E2 for ; Wed, 2 Sep 2020 15:51:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8880B2072A for ; Wed, 2 Sep 2020 15:51:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728238AbgIBPvg (ORCPT ); Wed, 2 Sep 2020 11:51:36 -0400 Received: from mail-oi1-f195.google.com ([209.85.167.195]:46752 "EHLO mail-oi1-f195.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726814AbgIBPvf (ORCPT ); Wed, 2 Sep 2020 11:51:35 -0400 Received: by mail-oi1-f195.google.com with SMTP id u126so4780867oif.13; Wed, 02 Sep 2020 08:51:34 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=6JeD4q3u5m7TYib0XXdTzqaKmJDZ9r459ZslYXgh8lw=; b=R0RP1QqWC6Vl5ns9rFZZPBpOcsrxGubYGd35tp7med77+8iTPnX0Njt0CTmQiDBc95 XuZDr6jM8PaZ2LrBdNNNG9d2En1Kt01RfUQP7VUKx7TAWoFmZTzzgBiKhF20Qwg7mlUU 1/TkmMXr1G++itn360HLqRXoNJwGBd1vCogIXoFZ5XZvp1AtkfySwNnrki6YvsEAnQJU KXOKimvFqqOe5PkjlTiHfsyv8StnnP6rPvR3aRgIEi5uPhl8z+bRIF7JEzNkWHJqJd9H fKNVj/42by9YxO1eV/xFnSckdLkJdhsoTipbZXREOFggzTt7tC3oKZ5g0Lt6TGiB9Ook 2opw== X-Gm-Message-State: AOAM531uSrSVMDskfGkG0AlrfGNMD5S1raKkQ/khFFP/FMXOsjC8Ja6y TbijvlGJiXWHLX1+oHUqxTY3D23tKR+rjs7gZK3638xx X-Google-Smtp-Source: ABdhPJxae6UIMdm5zyNbrXO7nReKqvFeikbvh88AnM0v5RcEpiean7ErLZWr+e2Mgvg5T/MqKiUm1LPR+XrJcw1TLSs= X-Received: by 2002:aca:d509:: with SMTP id m9mr2399947oig.71.1599061888397; Wed, 02 Sep 2020 08:51:28 -0700 (PDT) MIME-Version: 1.0 References: <20200901150438.228887-1-ulf.hansson@linaro.org> <20200901150654.GB30034@lst.de> <20200901154049.GA376@lst.de> <20200902134418.GR3265@brightrain.aerifal.cx> In-Reply-To: <20200902134418.GR3265@brightrain.aerifal.cx> From: Geert Uytterhoeven Date: Wed, 2 Sep 2020 17:51:16 +0200 Message-ID: Subject: Re: [PATCH v2] mmc: mmc_spi: Allow the driver to be built when CONFIG_HAS_DMA is unset To: Rich Felker Cc: Ulf Hansson , Christoph Hellwig , "linux-mmc@vger.kernel.org" , Mark Brown , Linux-sh list , Linux Kernel Mailing List Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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? ;-) Thanks! Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds