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=-5.1 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,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 E0B21C4741F for ; Mon, 9 Nov 2020 13:47:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8B3E9206B2 for ; Mon, 9 Nov 2020 13:47:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="CnkNa2H+" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730364AbgKINrO (ORCPT ); Mon, 9 Nov 2020 08:47:14 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56520 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729974AbgKINrN (ORCPT ); Mon, 9 Nov 2020 08:47:13 -0500 Received: from mail-qv1-xf43.google.com (mail-qv1-xf43.google.com [IPv6:2607:f8b0:4864:20::f43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 4C688C0613CF; Mon, 9 Nov 2020 05:47:13 -0800 (PST) Received: by mail-qv1-xf43.google.com with SMTP id ed14so4023687qvb.4; Mon, 09 Nov 2020 05:47:13 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:cc:references:from:autocrypt:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=3P4Xy4X3O8T4Nf4PgfEYUgS4xFf3jYJhHCyEVrGcPOA=; b=CnkNa2H+6dHsGG7oCncPC1SvCVCwADCa9oL2vYqCUUL6ad1Mh28I2FOsrm9mgoH5WX g55LdA13TrGDSXZ055BjdxAzQ0M9jIyGi3wzjqndyaXTv0IBwgw7Pc8MVJ5RDDjAgcIt 9ZR/1NXyTe7eLwblNB2plK5rsEMXcvcwrdKR3H2HTUllWkHNWUDrjyXm4oW2D0s72FOC zbg5CnVzs0TFt18VD/0akL0kKhkS2osuOx3UfPkM7UXHtE50ZJcrVUQ4wuc+5WMA1Cms hxWduHV+ffDJv0vlyOKvQsrU7c6OZuTvDYzNHKaSkBYFVxPVQkjnbZeHw7JJz4xD8F2Q e34g== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:autocrypt :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=3P4Xy4X3O8T4Nf4PgfEYUgS4xFf3jYJhHCyEVrGcPOA=; b=FtKc5rAT+AN6p3sV7dcYeq8yrw1vNkMlvjQTb77zzMP4kYMrnUspGSHgzd7nXlWxGR 4/pgoa1MCtCFV2LU2JYdLzNQsNx4wPtE+SKcKQe5rwpu6QI4MGW8ad98esVwGWHaraPM fijVJsCkuwK2r9rLKItzjyTZvKlRjcejpVoxXRz5ZQPcjTey+EaOLnDPjVC4C1VHenAC scSjIdFdhwk2ZBJxDgssKnf1a+bMZ44hzK7VVQ/vPR4HD73TiHZXrnA9HRNwgn+NxpEO vmlX4ggenQ7q+gOx4ZBIQjC+3yrbnonkdwZwlEMKH9BrqrRhhj82a/9MQiTHbnFBvJ+e Hbog== X-Gm-Message-State: AOAM531mwZFkTwnvhpcbisC5g2f5FVDy8gQL8ILDpgIVTXImJ3dL/k1I d2BDcKqxuntMmwBGPkd5LhQ= X-Google-Smtp-Source: ABdhPJzU05Fw0kzNgO7z+uoXZtYaKr3IfKDrqYuQ/4WUNUe6l+9tEW5JmP/HvpwEVZFqdcj9iMWp3Q== X-Received: by 2002:ad4:4e2f:: with SMTP id dm15mr1130200qvb.7.1604929632527; Mon, 09 Nov 2020 05:47:12 -0800 (PST) Received: from [192.168.1.201] (pool-108-51-35-162.washdc.fios.verizon.net. [108.51.35.162]) by smtp.googlemail.com with ESMTPSA id j50sm6081221qtc.5.2020.11.09.05.47.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 09 Nov 2020 05:47:11 -0800 (PST) Subject: Re: [PATCH 03/32] spi: dw: Fix driving MOSI low while recieving To: Mark Brown , Damien Le Moal Cc: Palmer Dabbelt , linux-riscv@lists.infradead.org, Rob Herring , Frank Rowand , devicetree@vger.kernel.org, Serge Semin , linux-spi@vger.kernel.org, Stephen Boyd , linux-clk@vger.kernel.org, Linus Walleij , linux-gpio@vger.kernel.org, Philipp Zabel References: <20201107081420.60325-1-damien.lemoal@wdc.com> <20201107081420.60325-4-damien.lemoal@wdc.com> <20201109132935.GB6380@sirena.org.uk> From: Sean Anderson Autocrypt: addr=seanga2@gmail.com; prefer-encrypt=mutual; keydata= mQENBFe74PkBCACoLC5Zq2gwrDcCkr+EPGsT14bsxrW07GiYzQhLCgwnPdEpgU95pXltbFhw 46GfyffABWxHKO2x+3L1S6ZxC5AiKbYXo7lpnTBYjamPWYouz+VJEVjUx9aaSEByBah5kX6a lKFZWNbXLAJh+dE1HFaMi3TQXXaInaREc+aO1F7fCa2zNE75ja+6ah8L4TPRFZ2HKQzve0/Y GXtoRw97qmnm3U36vKWT/m2AiLF619F4T1mHvlfjyd9hrVwjH5h/2rFyroXVXBZHGA9Aj8eN F2si35dWSZlIwXkNu9bXp0/pIu6FD0bI+BEkD5S7aH1G1iAcMFi5Qq2RNa041DfQSDDHABEB AAG0K1NlYW4gR2FsbGFnaGVyIEFuZGVyc29uIDxzZWFuZ2EyQGdtYWlsLmNvbT6JAVcEEwEK AEECGwMFCwkIBwIGFQgJCgsCBBYCAwECHgECF4ACGQEWIQSQYR1bzo1I0gPoYCg+6I/stKEQ bgUCXT+S2AUJB2TlXwAKCRA+6I/stKEQbhNOB/9ooea0hU9Sgh7PBloU6CgaC5mlqPLB7NTp +JkB+nh3Fqhk+qLZwzEynnuDLl6ESpVHIc0Ym1lyF4gT3DsrlGT1h0Gzw7vUwd1+ZfN0CuIx Rn861U/dAUjvbtN5kMBqOI4/5ea+0r7MACcIVnKF/wMXBD8eypHsorT2sJTzwZ6DRCNP70C5 N1ahpqqNmXe0uLdP0pu55JCqhrGw2SinkRMdWyhSxT56uNwIVHGhLTqH7Q4t1N6G1EH626qa SvIJsWlNpll6Y3AYLDw2/Spw/hqieS2PQ/Ky3rPZnvJt7/aSNYsKoFGX0yjkH67Uq8Lx0k1L w8jpXnbEPQN3A2ZJCbeM Message-ID: Date: Mon, 9 Nov 2020 08:47:10 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20201109132935.GB6380@sirena.org.uk> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-gpio@vger.kernel.org On 11/9/20 8:29 AM, Mark Brown wrote: > On Sat, Nov 07, 2020 at 05:13:51PM +0900, Damien Le Moal wrote: > >> The resting state of MOSI is high when nothing is driving it. If we >> drive it low while recieving, it looks like we are transmitting 0x00 >> instead of transmitting nothing. This can confuse slaves (like SD cards) >> which allow new commands to be sent over MOSI while they are returning >> data over MISO. The return of MOSI from 0 to 1 at the end of recieving >> a byte can look like a start bit and a transmission bit to an SD card. > > If client devices are interpreting the transmitted data then I would > expect the drivers for that hardware to be ensuring that whatever we > transmit matches what the device is expecting. We shouldn't be putting > a hack in a particular controller driver to paper over things, that will > mean that the device will break when used with other controllers and if > different devices have different requirements then obviously we can't > satisfy them. There is not meaningfully a general specification for SPI > which says what happens when signals are idle, it's all specific to the > client device. > > In this case it also looks like the controller hardware requires > transmit data and therefore should be setting SPI_MUST_TX and just > removing the in driver default anyway, though that will have no effect > one way or anther on the issue you're seeing. There is a recieve-only mode, but it is not used by this driver. Perhaps it should be. > Please also try to avoid the use of master/slave terminology where > reasonable, controller and device tend to work for SPI (though MOSI/MISO > are going to be harder to shift). Here I use it to draw distinction between the SPI master and the SPI slave, which are both devices in different contexts. --Sean