Path: csiph.com!weretis.net!feeder4.news.weretis.net!storethat.news.telefonica.de!telefonica.de!news.panservice.it!bofh.it!news.nic.it!robomod From: Andy Shevchenko Newsgroups: linux.kernel Subject: Re: Wrong "nollp" DW DMAC parameter value on ARC SDP. Date: Fri, 12 Aug 2016 13:10:01 +0200 Message-ID: References: X-Original-To: Eugeniy Paltsev , "dmaengine@vger.kernel.org" X-Extloop1: 1 X-Ironport-Av: E=Sophos;i="5.28,510,1464678000"; d="scan'208";a="747786348" Organization: Intel Finland Oy Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.20.4-1+b1 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: robomod@news.nic.it List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Approved: robomod@news.nic.it Lines: 47 X-Original-Cc: "linux-kernel@vger.kernel.org" , Nelson Pereira , "viresh.kumar@linaro.org" , "vinod.koul@intel.com" , "linux-snps-arc@lists.infradead.org" X-Original-Date: Fri, 12 Aug 2016 13:59:44 +0300 X-Original-Message-ID: <1470999584.4887.94.camel@linux.intel.com> X-Original-References: <1470988994.21247.33.camel@synopsys.com> X-Original-Sender: linux-kernel-owner@vger.kernel.org Xref: csiph.com linux.kernel:1461085 On Fri, 2016-08-12 at 08:03 +0000, Eugeniy Paltsev wrote: > Hi, > > "nollp" parameter defines if DW DMAC channel supports multi block > transfer or not. > > It is calculated in runtime, but differently depending on on > availability of pdata. If pdata is absent "nollp" is calculated using > autoconfig hardware registers. Otherwise "nollp" is calculated using > the next code construction: > channel_writel(dwc, LLP, DWC_LLP_LOC(0xffffffff)); > dwc->nollp = DWC_LLP_LOC(channel_readl(dwc, LLP)) == 0; > channel_writel(dwc, LLP, 0); > > I realized that these methods give different results. > For example on ARC AXS101 SDP in case of using autoconfig "nollp" was > calculated as "true" (and DMAC works fine),  > otherwise "nollp" was calculated as "false" (and DMAC doesn't work). Can you show out what the value you read back? > > So I'm wondering how the code in question really works? > From DW AHB DMAC databook I wasn't able to find anything relevant to > this tricky implementation. Could you please clarify a little but what > happens here? "Table 4-1: ... Hardcode Channel x LLP register to 0? ... Description: If set to 1, hardcodes channel x Linked List Pointer register to 0 (LLPx.LOC == 0), ..." > Maybe we should add "nollp" field in pdata structure and receive it > from pdata/device tree (like we use "is_private" or "is_memcpu" > fields) Yeah, perhaps we can remove that trick since we need this flag to be set on Intel Quark which might have the same issue as your case [1]. [1] http://www.spinics.net/lists/linux-serial/msg22948.html -- Andy Shevchenko Intel Finland Oy