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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 68C62C38A2A for ; Fri, 8 May 2020 19:27:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 54D47218AC for ; Fri, 8 May 2020 19:27:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727110AbgEHT1Q (ORCPT ); Fri, 8 May 2020 15:27:16 -0400 Received: from mga09.intel.com ([134.134.136.24]:41791 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726797AbgEHT1P (ORCPT ); Fri, 8 May 2020 15:27:15 -0400 IronPort-SDR: tbv4hXfWchF6PCZmTplrmPmt7/LAXTeO/c8ByLxhYYEPwakH0iqNA1yp0VghnXTwQZx/UTC7tQ lJEnjiAbygmA== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga008.fm.intel.com ([10.253.24.58]) by orsmga102.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 08 May 2020 12:27:14 -0700 IronPort-SDR: pF8J1l9o4UpgFzGa4LQtsBx8ZZ5N7thHTdGIUSDujb0t2rGFj6tppeSRizzVjKjK8TeeEQPU9X yLJeu0cRBDUA== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,368,1583222400"; d="scan'208";a="252042190" Received: from smile.fi.intel.com (HELO smile) ([10.237.68.40]) by fmsmga008.fm.intel.com with ESMTP; 08 May 2020 12:27:08 -0700 Received: from andy by smile with local (Exim 4.93) (envelope-from ) id 1jX8eM-005T81-HP; Fri, 08 May 2020 22:27:10 +0300 Date: Fri, 8 May 2020 22:27:10 +0300 From: Andy Shevchenko To: Serge Semin Cc: Mark Brown , Serge Semin , Georgy Vlasov , Ramil Zaripov , Alexey Malahov , Thomas Bogendoerfer , Paul Burton , Ralf Baechle , Arnd Bergmann , Allison Randal , Gareth Williams , Rob Herring , linux-mips@vger.kernel.org, devicetree@vger.kernel.org, Linus Walleij , Greg Kroah-Hartman , Xinwei Kong , Thor Thayer , Charles Keepax , "wuxu.wu" , Phil Edworthy , Thomas Gleixner , Jarkko Nikula , linux-spi@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 16/17] spi: dw: Fix Rx-only DMA transfers Message-ID: <20200508192710.GV185537@smile.fi.intel.com> References: <20200508132943.9826-1-Sergey.Semin@baikalelectronics.ru> <20200508132943.9826-17-Sergey.Semin@baikalelectronics.ru> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200508132943.9826-17-Sergey.Semin@baikalelectronics.ru> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, May 08, 2020 at 04:29:41PM +0300, Serge Semin wrote: > Tx-only DMA transfers are working perfectly fine since in this case > the code just ignores the Rx FIFO overflow interrupts. But it turns > out the SPI Rx-only transfers are broken since nothing pushing any > data to the shift registers, so the Rx FIFO is left empty and the > SPI core subsystems just returns a timeout error. Since DW DMAC > driver doesn't support something like cyclic write operations of > a single byte to a device register, the only way to support the > Rx-only SPI transfers is to fake it by using a dummy Tx-buffer. > This is what we intend to fix in this commit by setting the > SPI_CONTROLLER_MUST_TX flag for DMA-capable platform. Hmm... If Mark consider this a right thing to do, then it's fine. I didn't investigate what this flag may produce as a side effect. > --- a/drivers/spi/spi-dw.c > +++ b/drivers/spi/spi-dw.c > @@ -524,6 +524,7 @@ int dw_spi_add_host(struct device *dev, struct dw_spi *dws) > dws->dma_inited = 0; > } else { > master->can_dma = dws->dma_ops->can_dma; > + master->flags |= SPI_CONTROLLER_MUST_TX; > } > } > > -- > 2.25.1 > -- With Best Regards, Andy Shevchenko