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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,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 09EF4C433E0 for ; Mon, 15 Jun 2020 07:19:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DBA2B206E2 for ; Mon, 15 Jun 2020 07:19:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592205578; bh=sUsoYboFQvARlrHTsUiM3cD/BcO9o1B8GEAGyFExK74=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=zXAx96P2raLHR7M5yT2om9AxFH29k7YY020fDnkNObsbGvHyd+VgYTkYKx8PnO058 JkRw7KMTkzYatXFTz25sJ3EyuMEf1ONTTMvdztGTDnR0aPFDcgH9WoY3eRMqbTb4Dm bqnuPt85ekaV3sC/4T5uqGb8GnrwXCZE0Dtk1BvE= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728556AbgFOHTh (ORCPT ); Mon, 15 Jun 2020 03:19:37 -0400 Received: from mail.kernel.org ([198.145.29.99]:37906 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728417AbgFOHTg (ORCPT ); Mon, 15 Jun 2020 03:19:36 -0400 Received: from localhost (unknown [171.61.66.58]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id E3B20206D7; Mon, 15 Jun 2020 07:19:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1592205575; bh=sUsoYboFQvARlrHTsUiM3cD/BcO9o1B8GEAGyFExK74=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hX5i481ti5uYsYfjR/Sys+++2YWQBXqKyMhY/nyXTZJa7t1hCPaq5YJrQbzTkKRF/ 77ipSxJq9l/mLcTdE6/Qa8hj7e3xFezC0EhH1hgmKtR7uTTBgAJLdh6w0LPf35xvvP 2qAqtlDOGdeHKH/hC+vYmb0SZDCN0s/5y4Ux1Du0= Date: Mon, 15 Jun 2020 12:49:31 +0530 From: Vinod Koul To: Robin Gong Cc: Mark Brown , "shawnguo@kernel.org" , "s.hauer@pengutronix.de" , "festevam@gmail.com" , "robin.murphy@arm.com" , "matthias.schiffer@ew.tq-group.com" , "kernel@pengutronix.de" , dl-linux-imx , "linux-spi@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" Subject: Re: [PATCH v1 RFC 1/2] spi: introduce fallback to pio Message-ID: <20200615071931.GK1393454@vkoul-mobl> References: <1591880310-1813-1-git-send-email-yibin.gong@nxp.com> <1591880310-1813-2-git-send-email-yibin.gong@nxp.com> <20200611134042.GG4671@sirena.org.uk> <20200612101357.GA5396@sirena.org.uk> <20200612141611.GI5396@sirena.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 14-06-20, 13:04, Robin Gong wrote: > On 2020/06/12 22:16 Mark Brown wrote: > > On Fri, Jun 12, 2020 at 01:48:41PM +0000, Robin Gong wrote: > > > On 2020/06/12 18:14 Mark Brown wrote: > > > > > > Please look at the formatting of your e-mails - they're really hard > > > > to read. The line length is over 80 columns and there's no breaks between > > paragraphs. > > > > > Sorry for that, seems my outlook format issue, hope it's ok now this > > > time :) > > > > Yes, looks good thanks! > > > > > > Client could enable this feature by choosing SPI_MASTER_FALLBACK > > > > freely without any impact on others. > > > > > > SPI_MASTER_FALLBACK. If this works why would any driver not enable > > > > the flag? > > > > > Just make sure little impact if it's not good enough and potential > > > issue may come out after it's merged into mainline. TBH, I'm not sure > > > if it has taken care all in spi core. Besides, I don't know if other spi client need > > this feature. > > > > It's not something that's going to come up a lot for most devices, it'd be a > > mapping failure due to running out of memory or something, but your point > > about that being possible is valid. > > > > > > > Any error happen in DMA could fallback to PIO , seems a nice to > > > > > have, > > > > because it could > > > > > give chance to run in PIO which is more reliable. But if there is > > > > > also error in > > > > > > PIO, thus may loop here, it's better adding limit try times here? > > > > > > An error doesn't mean nothing happened on the bus, an error could > > > > for example also be something like a FIFO overrun which corrupts data. > > > > > Do you mean fallback to PIO may cause FIFO overrun since some latency > > > involved so that this patch seems not useful as expected? > > > > No, I mean that the reason the DMA transfer fails may be something that > > happens after we've started putting things on the bus - the bit about FIFOs is > > just a random example of an error that could happen. > > > Sorry Mark for that I can't get your point... The bus error such as data corrupt > seems not the spi core's business since it can only be caught in spi controller > driver or upper level such as mtd driver (spi-nor) which know what's the failure > happen at spi bus HW level or what's the correct data/message. In other words, > spi core can't detect such error by transfer_one(). > > > > > It *could* but only in extreme situations, and again this isn't just > > > > handling errors from failure to prepare the hardware but also > > > > anything that happens after it. > > > > > Okay, understood your point. You prefer to some interface provided by > > > dma engine before dmaengine_prep_slave_sg so that can_dma() can know > > > if this dma channel is ready indeed. But unfortunately, seems there is no > > one.... > > > > Well, this is free software and everything can be modified! The other option > > would be framework changes in SPI that allowed us to indicate from the driver > > that an error occured before we started doing anything to the hardware (like > > happens here) through something like a special error code or splitting up the > > API. > Yes, but both assume spi controller driver could detect such dma failure before > dmaengine_prep_*(). Let's wait Vinod's comment for that if dmaengine_slave_config > could keep direction. The direction is already in the prep_ call, so sending in dmaengine_slave_config is not required, pls pass it in the prep_ call > But despite of that case, do you think this patch is valid for transfer_one() failue > in dma and fallback to pio? -- ~Vinod