From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755801AbcI2NDA (ORCPT ); Thu, 29 Sep 2016 09:03:00 -0400 Received: from arroyo.ext.ti.com ([198.47.19.12]:49169 "EHLO arroyo.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754863AbcI2NCw (ORCPT ); Thu, 29 Sep 2016 09:02:52 -0400 Subject: Re: [PATCH 0/4] Add DMA support for ti_am335x_adc driver To: Jonathan Cameron , References: <20160921161134.6951-1-mugunthanvnm@ti.com> <22588f2d-d0de-7911-35ed-92094f7dd28d@kernel.org> CC: Tony Lindgren , Rob Herring , Mark Rutland , Russell King , Hartmut Knaack , Lars-Peter Clausen , Peter Meerwald-Stadler , Lee Jones , Vignesh R , "Andrew F . Davis" , , , , , Sekhar Nori , Peter Ujfalusi From: Mugunthan V N Message-ID: Date: Thu, 29 Sep 2016 18:31:30 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <22588f2d-d0de-7911-35ed-92094f7dd28d@kernel.org> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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