From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752633AbeEVDiB (ORCPT ); Mon, 21 May 2018 23:38:01 -0400 Received: from mail-pg0-f67.google.com ([74.125.83.67]:46602 "EHLO mail-pg0-f67.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751724AbeEVDhz (ORCPT ); Mon, 21 May 2018 23:37:55 -0400 X-Google-Smtp-Source: AB8JxZrhwaty4OeCysmuZZXq8HxMQg/ThYftCY/ZX5DOL5yA9QRO+pmTAjqde3Da8yvffToixUUPpg== Date: Tue, 22 May 2018 09:07:51 +0530 From: Vinod Koul To: Frank Mori Hess Cc: Marek Szyprowski , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, Dan Williams , r.baldyga@hackerion.com, Krzysztof Kozlowski , Bartlomiej Zolnierkiewicz , Linux Samsung SOC Subject: Re: Revert "dmaengine: pl330: add DMA_PAUSE feature" Message-ID: <20180522033751.GB18351@vkoul-mobl> References: <06f54061-c537-b399-e493-ec2cdf4def5d@samsung.com> <20180515062144.GC13271@vkoul-mobl> <20180517041946.GQ13271@vkoul-mobl> <20180518040349.GB2932@vkoul-mobl> <20180521091626.GB14654@vkoul-mobl> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.2 (2017-12-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 21-05-18, 20:56, Frank Mori Hess wrote: > On Mon, May 21, 2018 at 5:16 AM, Vinod Koul wrote: > >> > >> I understand the residue can't be read after terminate, that's why > >> reading the residue is step 2 in pause/residue/terminate. My question > >> was whether the entire sequence pause/residue/terminate taken as a > >> whole can or cannot lose data. Saying that individual steps can or > >> can't lose data is not enough, context is required. The key point is > >> whether pause flushes in-flight data to its destination or not. If it > >> does, and our residue is accurate, the terminate cannot cause data > >> loss. If pause doesn't flush, an additional step of flush_sync as > >> Lars suggested is required. So pause/flush_sync/residue/terminate > >> would be the safe sequence that cannot lose data. > > > > I wouldn't use cannot, shouldn't would be better here as it depends on HW and > > where all data has been buffered and if it can be flushed or not. > > > > Have you checked if pl330 supports such flushing? > > It does not, at least in the context of pausing. The dma-330 DMAEND > instruction flushes in-flight data to its destination, and there are > read/write barrier instructions also, but none of them can be injected > on the fly into a running dma thread. DMAKILL can be, but it discards > in-flight data. Currently, if an 8250 serial driver uses the pl330 > for rx dma, the result is possible data loss/corruption. If there was > a stronger pause capability, call it "cmd_sync_pause" which guaranteed > flushing of in-flight data to its destination and accurate residue > reading when paused, then the 8250 serial driver could check for > "cmd_sync_pause" and reject dma drivers that do not have that > capability. pl330.c would not advertise cmd_sync_pause. I don't know > if other dmaengine hardware would be able to support cmd_sync_pause or > not, I'm mostly just familiar with the pl330. The ep93xx_dma.c driver > for example has a m2p_hw_synchronize function which seems to do a > flush. Well looks like even adding support for sync_pause doesn't solve your issue on pl330. Do you want to move this to PIO mode then..? -- ~Vinod