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=-4.0 required=3.0 tests=BAYES_00, 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 8CBB8C433E6 for ; Wed, 15 Jul 2020 17:08:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6B4C42065E for ; Wed, 15 Jul 2020 17:08:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725867AbgGORIt (ORCPT ); Wed, 15 Jul 2020 13:08:49 -0400 Received: from mail.baikalelectronics.com ([87.245.175.226]:38260 "EHLO mail.baikalelectronics.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725838AbgGORIt (ORCPT ); Wed, 15 Jul 2020 13:08:49 -0400 Received: from localhost (unknown [127.0.0.1]) by mail.baikalelectronics.ru (Postfix) with ESMTP id A28E5803202D; Wed, 15 Jul 2020 17:08:45 +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 u5_RIfGIlZua; Wed, 15 Jul 2020 20:08:45 +0300 (MSK) Date: Wed, 15 Jul 2020 20:08:43 +0300 From: Serge Semin To: Vinod Koul CC: Serge Semin , Peter Ujfalusi , Viresh Kumar , Dan Williams , Andy Shevchenko , Alexey Malahov , Thomas Bogendoerfer , Arnd Bergmann , Rob Herring , , , , Subject: Re: [PATCH v7 04/11] dmaengine: Introduce max SG list entries capability Message-ID: <20200715170843.w4rwl7zjwfcr7rg2@mobilestation> References: <20200709224550.15539-1-Sergey.Semin@baikalelectronics.ru> <20200709224550.15539-5-Sergey.Semin@baikalelectronics.ru> <20200710092738.z7zyywe46mp7uuf3@mobilestation> <427bc5c8-0325-bc25-8637-a7627bcac26f@ti.com> <20200710161445.t6eradkgt4terdr3@mobilestation> <20200715111315.GK34333@vkoul-mobl> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: <20200715111315.GK34333@vkoul-mobl> X-ClientProxiedBy: MAIL.baikal.int (192.168.51.25) To mail (192.168.51.25) Sender: dmaengine-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: dmaengine@vger.kernel.org On Wed, Jul 15, 2020 at 04:43:15PM +0530, Vinod Koul wrote: > On 10-07-20, 19:14, Serge Semin wrote: > > On Fri, Jul 10, 2020 at 02:51:33PM +0300, Peter Ujfalusi wrote: > > > > Since we should be able to handle longer lists and this is kind of a > > > hint for clients that above this number of nents the list will be broken > > > up to smaller 'bursts', which when traversing could cause latency. > > > > > > sg_chunk_len might be another candidate. > > > > Ok. We've got four candidates: > > - max_sg_nents_burst > > - max_sg_burst > > - max_sg_chain > > - sg_chunk_len > > > > @Vinod, @Andy, what do you think? > > So IIUC your hw supports single sg and in that you would like to publish > the length of each chunk, is that correct? No. My DMA engine does support only a single-entry SG-list, but the new DMA {~~slave~~,channel,device,peripheral,...} capability isn't about the length, but is about the maximum number of SG-list entries a DMA engine is able to automatically/"without software help" walk through and execute. In this thread we are debating about that new capability naming. The name suggested in this patch: max_sg_nents. Peter noted (I mostly agree with him), that it might be ambiguous, since from it (without looking into the dma_slave_caps structure comment) a user might think that it's a maximum number of SG-entries, which can be submitted for the DMA engine execution, while in fact it's about the DMA engine capability of automatic/burst/"without software intervention" SG-list entries walking through. (Such information will be helpful to solve a problem discussed in this mailing thread, and described in the cover-letter to this patchset. We also discussed it with you and Andy in the framework of this patchset many times.) As an alternative Peter suggested: max_sg_nents_burst. I also think it's better than "max_sg_nents" but for me it seems a bit long. max_sg_burst seems better. There is no need in having the "nents" in the name, since SG-list implies a list, which main parameter (if not to say only parameter) is the number of entries. "burst" is pointing out to the automatic/accelerated/"without software intervention" SG-list entries walking through. On the second thought suggested by me "max_sg_chain" sounds worse than "max_sg_burst", because it also might be perceived as a parameter limiting the number of SG-list entries is able to be submitted for the DMA engine execution, while in fact it describes another matter. Regarding "sg_chunk_len". I think it's ambiguous too, since the "chunk length" might be referred to both the entries length and to the sub-SG-list length. So what do you think? What name is better describing the new DMA capability? -Sergey > If so sg_chunk_len seems apt.. > > -- > ~Vinod