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=-0.7 required=3.0 tests=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 DE265C433E0 for ; Fri, 29 May 2020 09:56:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id C391420776 for ; Fri, 29 May 2020 09:56:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725839AbgE2J4s (ORCPT ); Fri, 29 May 2020 05:56:48 -0400 Received: from mail.baikalelectronics.com ([87.245.175.226]:46958 "EHLO mail.baikalelectronics.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725681AbgE2J4s (ORCPT ); Fri, 29 May 2020 05:56:48 -0400 Received: from localhost (unknown [127.0.0.1]) by mail.baikalelectronics.ru (Postfix) with ESMTP id E2EF08030807; Fri, 29 May 2020 09:56:44 +0000 (UTC) X-Virus-Scanned: amavisd-new at baikalelectronics.ru Received: from mail.baikalelectronics.ru ([127.0.0.1]) by localhost (mail.baikalelectronics.ru [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Vh2S5JHfX0OB; Fri, 29 May 2020 12:56:44 +0300 (MSK) Date: Fri, 29 May 2020 12:56:43 +0300 From: Serge Semin To: Andy Shevchenko CC: Serge Semin , Mark Brown , Georgy Vlasov , Ramil Zaripov , Alexey Malahov , Thomas Bogendoerfer , Arnd Bergmann , Feng Tang , Rob Herring , , devicetree , linux-spi , Linux Kernel Mailing List Subject: Re: [PATCH v5 03/16] spi: dw: Locally wait for the DMA transactions completion Message-ID: <20200529095643.q3pa5lqg63dgf3kf@mobilestation> References: <20200529035915.20790-1-Sergey.Semin@baikalelectronics.ru> <20200529035915.20790-4-Sergey.Semin@baikalelectronics.ru> <20200529081204.e2j5unvvfikr2y7v@mobilestation> <20200529092610.GX1634618@smile.fi.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20200529092610.GX1634618@smile.fi.intel.com> X-ClientProxiedBy: MAIL.baikal.int (192.168.51.25) To mail (192.168.51.25) 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 12:26:10PM +0300, Andy Shevchenko wrote: > 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! Agreed. I'll create a more detailed commit description, which will have the info you cited. -Sergey > > -- > With Best Regards, > Andy Shevchenko > >