From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935685AbcI3Dh1 (ORCPT ); Thu, 29 Sep 2016 23:37:27 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:35727 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752583AbcI3DhX (ORCPT ); Thu, 29 Sep 2016 23:37:23 -0400 Content-Type: text/plain; charset=windows-1252 Mime-Version: 1.0 (Mac OS X Mail 9.3 \(3124\)) Subject: Re: [PATCH 0/4] Add DMA support for ti_am335x_adc driver From: John Syne In-Reply-To: Date: Thu, 29 Sep 2016 20:37:19 -0700 Cc: Jonathan Cameron , linux-iio@vger.kernel.org, Tony Lindgren , Rob Herring , Mark Rutland , Russell King , Hartmut Knaack , Lars-Peter Clausen , Peter Meerwald-Stadler , Lee Jones , Vignesh R , "Andrew F . Davis" , linux-omap@vger.kernel.org, devicetree@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, Sekhar Nori , Peter Ujfalusi Message-Id: References: <20160921161134.6951-1-mugunthanvnm@ti.com> <22588f2d-d0de-7911-35ed-92094f7dd28d@kernel.org> To: Mugunthan V N X-Mailer: Apple Mail (2.3124) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: 8bit X-MIME-Autoconverted: from quoted-printable to 8bit by mail.home.local id u8U3bVDA025141 I applied your patches to the following kernel: github.com/RobertCNelson/bb-kernel.git branch am33x-v4.8 Changing #define REG_DMAENABLE_CLEAR 0x038 to #define REG_DMAENABLE_CLEAR 0x03C Also applying the following DTS changes: target = <&tscadc>; __overlay__ { status = "okay"; adc { ti,adc-channels = <0 1 2 3 4 5 6>; ti,chan-step-avg = <0x1 0x1 0x1 0x1 0x1 0x1 0x1>; ti,chan-step-opendelay = <0x0 0x0 0x0 0x0 0x0 0x0 0x0>; ti,chan-step-sampledelay = <0x0 0x0 0x0 0x0 0x0 0x0 0x0>; }; }; Running on a BeagleBoneBlack, I was able to stream samples at 200ksps continuously and it looked stable. htop showed CPU utilization between 5% and 7% Thank you for getting this to work. Regards, John > On Sep 29, 2016, at 6:01 AM, Mugunthan V N wrote: > > On Sunday 25 September 2016 03:11 PM, Jonathan Cameron wrote: >> On 21/09/16 17:11, Mugunthan V N wrote: >>>> The ADC has a 64 work depth fifo length which holds the ADC data >>>> till the CPU reads. So when a user program needs a large ADC data >>>> to operate on, then it has to do multiple reads to get its >>>> buffer. Currently if the application asks for 4 samples per >>>> channel with all 8 channels are enabled, kernel can provide only >>>> 3 samples per channel when all 8 channels are enabled (logs at >>>> [1]). So with DMA support user can request for large number of >>>> samples at a time (logs at [2]). >>>> >>>> Tested the patch on AM437x-gp-evm and AM335x Boneblack with the >>>> patch [3] to enable ADC and pushed a branch for testing [4] >>>> >>>> [1] - http://pastebin.ubuntu.com/23211490/ >>>> [2] - http://pastebin.ubuntu.com/23211492/ >>>> [3] - http://pastebin.ubuntu.com/23211494/ >>>> [4] - git://git.ti.com/~mugunthanvnm/ti-linux-kernel/linux.git iio-dma >> Just curious. How fast is the ADC sampling at in these? Never that >> obvious for this driver! >> >> I'm also curious as to whether you started to hit the limits of the >> kfifo based interface. Might be worth considering adding alternative >> support for the dma buffers interface which is obviously much lower >> overhead. >> >> Good to have this work prior to that as the kfifo stuff is somewhat >> easier to use. > > Currently ADC clock is 3MHz, which can produce a data rate of 225KBps > per channel with no open delay and no averaging of samples. So when all > 8 Channels are enables the data rate will be 1.75MBps > > ADC can be operated at 24MHz, which can generate a data rate of 28MBps > with all 8 channels enabled and no open delay and averaging, but our > target is to get 800K samples per second per channel which has a data > rate of 12.5MBps > > I think with this data rate, DMA will be the best option to implement > without any data loss and less cpu overload to read the ADC samples. > > Regards > Mugunthan V N > -- > To unsubscribe from this list: send the line "unsubscribe linux-omap" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html