From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andy Gross Subject: Re: [PATCH] dmaengine: qcom_bam_dma: Add descriptor flag APIs Date: Thu, 22 May 2014 10:32:14 -0500 Message-ID: <20140522153214.GB22327@qualcomm.com> References: <1397772242-4048-1-git-send-email-agross@codeaurora.org> <20140502162841.GZ32284@intel.com> <20140502180827.GA9476@qualcomm.com> <20140515173206.GA16858@qualcomm.com> <20140522061049.GW21128@intel.com> <20140522150906.GA22327@qualcomm.com> <537E1749.1030505@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from smtp.codeaurora.org ([198.145.11.231]:60376 "EHLO smtp.codeaurora.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751187AbaEVPcQ (ORCPT ); Thu, 22 May 2014 11:32:16 -0400 Content-Disposition: inline In-Reply-To: <537E1749.1030505@linaro.org> Sender: linux-arm-msm-owner@vger.kernel.org List-Id: linux-arm-msm@vger.kernel.org To: Srinivas Kandagatla Cc: Vinod Koul , dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-arm-msm@vger.kernel.org On Thu, May 22, 2014 at 04:27:05PM +0100, Srinivas Kandagatla wrote: > > > >The EOT is not used for every transaction. It is part of a handshaking > >protocol with the attached peripheral, much like the NWD (notify when done). As > >near as I can tell today, no peripheral depends on the EOB, so we could drop it > >for now until it is needed and cross this bridge when we need to. > > As EOT behaviour is totally dependent on the attached peripheral(or > channel), Can't we make this specific to channel by passing > additional flags in the DT dma channel descriptors? This will be > better abstraction for drivers as well. Even for channels where you want to use EOT, you don't use it for every transaction. So a global channel flag isn't going to work. This is the same for NWD. It is a per descriptor choice. > > I know that EOT flag is part of descriptor but still some channels > *must* have EOT to run there state-machine correctly. So making it > optional for those channels might be wrong. > > Are there any use cases for particular *channel* where EOT > requirement changes dynamically? I2C is one example. You place EOT on the last transaction that makes up a write/read transaction. You may have multiple descriptors to send data, but the last one has EOT. And for read transactions, you place NWD on the last read transaction. -- sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation From mboxrd@z Thu Jan 1 00:00:00 1970 From: agross@codeaurora.org (Andy Gross) Date: Thu, 22 May 2014 10:32:14 -0500 Subject: [PATCH] dmaengine: qcom_bam_dma: Add descriptor flag APIs In-Reply-To: <537E1749.1030505@linaro.org> References: <1397772242-4048-1-git-send-email-agross@codeaurora.org> <20140502162841.GZ32284@intel.com> <20140502180827.GA9476@qualcomm.com> <20140515173206.GA16858@qualcomm.com> <20140522061049.GW21128@intel.com> <20140522150906.GA22327@qualcomm.com> <537E1749.1030505@linaro.org> Message-ID: <20140522153214.GB22327@qualcomm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Thu, May 22, 2014 at 04:27:05PM +0100, Srinivas Kandagatla wrote: > > > >The EOT is not used for every transaction. It is part of a handshaking > >protocol with the attached peripheral, much like the NWD (notify when done). As > >near as I can tell today, no peripheral depends on the EOB, so we could drop it > >for now until it is needed and cross this bridge when we need to. > > As EOT behaviour is totally dependent on the attached peripheral(or > channel), Can't we make this specific to channel by passing > additional flags in the DT dma channel descriptors? This will be > better abstraction for drivers as well. Even for channels where you want to use EOT, you don't use it for every transaction. So a global channel flag isn't going to work. This is the same for NWD. It is a per descriptor choice. > > I know that EOT flag is part of descriptor but still some channels > *must* have EOT to run there state-machine correctly. So making it > optional for those channels might be wrong. > > Are there any use cases for particular *channel* where EOT > requirement changes dynamically? I2C is one example. You place EOT on the last transaction that makes up a write/read transaction. You may have multiple descriptors to send data, but the last one has EOT. And for read transactions, you place NWD on the last read transaction. -- sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, hosted by The Linux Foundation