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=-0.5 required=3.0 tests=DKIM_ADSP_CUSTOM_MED, FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM,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 8E2CFC433E0 for ; Fri, 29 May 2020 09:26:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 714FD2072D for ; Fri, 29 May 2020 09:26:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726282AbgE2J0M (ORCPT ); Fri, 29 May 2020 05:26:12 -0400 Received: from mga05.intel.com ([192.55.52.43]:42856 "EHLO mga05.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725790AbgE2J0M (ORCPT ); Fri, 29 May 2020 05:26:12 -0400 IronPort-SDR: 1fW3LORCQsV7Ek5VdS+OJCo8gEgzD6OCL1l5m4fnWR2F2WOE3TMpqVLQQIdcKQjCpgF2UStt/V xjSrFyM686xA== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga004.jf.intel.com ([10.7.209.38]) by fmsmga105.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 May 2020 02:26:11 -0700 IronPort-SDR: eV3HSNzOlNkNU0dRGF6h01o7RWVOKKfgkYKSky63r56KGxKAekid2lcuvuTGLbJcyagbUx4KIN cKkcGqv52ezg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,448,1583222400"; d="scan'208";a="414915783" Received: from smile.fi.intel.com (HELO smile) ([10.237.68.40]) by orsmga004.jf.intel.com with ESMTP; 29 May 2020 02:26:08 -0700 Received: from andy by smile with local (Exim 4.93) (envelope-from ) id 1jebHG-009aJ4-Qp; Fri, 29 May 2020 12:26:10 +0300 Date: Fri, 29 May 2020 12:26:10 +0300 From: Andy Shevchenko To: Serge Semin Cc: Serge Semin , Mark Brown , Georgy Vlasov , Ramil Zaripov , Alexey Malahov , Thomas Bogendoerfer , Arnd Bergmann , Feng Tang , Rob Herring , linux-mips@vger.kernel.org, devicetree , linux-spi , Linux Kernel Mailing List Subject: Re: [PATCH v5 03/16] spi: dw: Locally wait for the DMA transactions completion Message-ID: <20200529092610.GX1634618@smile.fi.intel.com> References: <20200529035915.20790-1-Sergey.Semin@baikalelectronics.ru> <20200529035915.20790-4-Sergey.Semin@baikalelectronics.ru> <20200529081204.e2j5unvvfikr2y7v@mobilestation> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200529081204.e2j5unvvfikr2y7v@mobilestation> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo Sender: linux-mips-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Fri, May 29, 2020 at 11:12:04AM +0300, Serge Semin wrote: > On Fri, May 29, 2020 at 10:55:32AM +0300, Andy Shevchenko wrote: > > On Fri, May 29, 2020 at 7:02 AM Serge Semin > > wrote: > > > > > > Even if DMA transactions are finished it doesn't mean that the SPI > > > transfers are also completed. It's specifically concerns the Tx-only > > > SPI transfers, since there might be data left in the SPI Tx FIFO after > > > the DMA engine notifies that the Tx DMA procedure is done. In order to > > > completely fix the problem first the driver has to wait for the DMA > > > transaction completion, then for the corresponding SPI operations to be > > > finished. In this commit we implement the former part of the solution. > > > > > > Note we can't just move the SPI operations wait procedure to the DMA > > > completion callbacks, since these callbacks might be executed in the > > > tasklet context (and they will be in case of the DW DMA). In case of > > > slow SPI bus it can cause significant system performance drop. > > > > > I read commit message, I read the code. What's going on here since you > > repeated xfer_completion (and its wait routine) from SPI core and I'm > > wondering what happened to it? Why we are not calling > > spi_finalize_current_transfer()? > > We discussed that in v4. You complained about using ndelay() for slow SPI bus, > which may cause too long atomic context execution. We agreed. Since we can't wait > in the tasklet context and using a dedicated kernel thread for waiting would be too > much, Me and Mark agreed, that > even if it causes us of the local wait-function > re-implementation the best approach would be not to use the generic > spi_transfer_wait() method, but instead wait for the DMA transactions locally > in the DMA driver and just return 0 from the transfer_one callback indicating > that the SPI transfer is finished and there is no need for SPI core to wait. As > a lot of DMA-based SPI drivers do. The above is missed in the commit message. > If you don't understand what the commit message says, just say so. I'll > reformulate it. See above. A bit of elaboration would be good. Thank you! -- With Best Regards, Andy Shevchenko