Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754237AbaBDKgI (ORCPT ); Tue, 4 Feb 2014 05:36:08 -0500 Received: from mail-la0-f42.google.com ([209.85.215.42]:35843 "EHLO mail-la0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751453AbaBDKfz (ORCPT ); Tue, 4 Feb 2014 05:35:55 -0500 MIME-Version: 1.0 In-Reply-To: <20140204052810.GO10628@intel.com> References: <1390409565-4200-1-git-send-email-sthokal@xilinx.com> <1390409565-4200-2-git-send-email-sthokal@xilinx.com> <52E0FC22.8060903@metafoo.de> <52E2698B.6070001@metafoo.de> <20140126135933.GD10628@intel.com> <20140204052810.GO10628@intel.com> Date: Tue, 4 Feb 2014 16:05:53 +0530 X-Google-Sender-Auth: OnuCPTQVccstrMGbPfH_MivOkhY Message-ID: Subject: Re: [PATCH v2] dma: Add Xilinx AXI Video Direct Memory Access Engine driver support From: Srikanth Thokala To: Vinod Koul Cc: Srikanth Thokala , Lars-Peter Clausen , dan.j.williams@intel.com, michal.simek@xilinx.com, Grant Likely , robh+dt@kernel.org, linux-arm-kernel@lists.infradead.org, "linux-kernel@vger.kernel.org" , devicetree@vger.kernel.org, dmaengine@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Feb 4, 2014 at 10:58 AM, Vinod Koul wrote: > On Fri, Jan 31, 2014 at 12:22:52PM +0530, Srikanth Thokala wrote: >> >>> >> [...] >> >>> >>> +/** >> >>> >>> + * xilinx_vdma_device_control - Configure DMA channel of the device >> >>> >>> + * @dchan: DMA Channel pointer >> >>> >>> + * @cmd: DMA control command >> >>> >>> + * @arg: Channel configuration >> >>> >>> + * >> >>> >>> + * Return: '0' on success and failure value on error >> >>> >>> + */ >> >>> >>> +static int xilinx_vdma_device_control(struct dma_chan *dchan, >> >>> >>> + enum dma_ctrl_cmd cmd, unsigned long arg) >> >>> >>> +{ >> >>> >>> + struct xilinx_vdma_chan *chan = to_xilinx_chan(dchan); >> >>> >>> + >> >>> >>> + switch (cmd) { >> >>> >>> + case DMA_TERMINATE_ALL: >> >>> >>> + xilinx_vdma_terminate_all(chan); >> >>> >>> + return 0; >> >>> >>> + case DMA_SLAVE_CONFIG: >> >>> >>> + return xilinx_vdma_slave_config(chan, >> >>> >>> + (struct xilinx_vdma_config *)arg); >> >>> >> >> >>> >> You really shouldn't be overloading the generic API with your own semantics. >> >>> >> DMA_SLAVE_CONFIG should take a dma_slave_config and nothing else. >> >>> > >> >>> > Ok. The driver needs few additional configuration from the slave >> >>> > device like Vertical >> >>> > Size, Horizontal Size, Stride etc., for the DMA transfers, in that case do you >> >>> > suggest me to define a separate dma_ctrl_cmd like the one FSLDMA_EXTERNAL_START >> >>> > defined for Freescale drivers? >> >>> >> >>> In my opinion it is not a good idea to have driver implement a generic API, >> >>> but at the same time let the driver have custom semantics for those API >> >>> calls. It's a bit like having a gpio driver that expects 23 and 42 as the >> >>> values passed to gpio_set_value instead of 0 and 1. It completely defeats >> >>> the purpose of a generic API, namely that you are able to write generic code >> >>> that makes use of the API without having to know about which implementation >> >>> API it is talking to. The dmaengine framework provides the >> >>> dmaengine_prep_interleaved_dma() function to setup two dimensional >> >>> transfers, e.g. take a look at sirf-dma.c or imx-dma.c. >> >> >> >> The question here i think would be waht this device supports? Is the hardware >> >> capable of doing interleaved transfers, then would make sense. >> >> >> >> While we do try to get users use dma_slave_config, but there will always be >> >> someone who have specfic params. If we can generalize then we might want to add >> >> to the dma_slave_config as well >> > >> > There are many configuration parameters which are specific to IP and I >> > would like to >> > give an overview of some of parameteres here: >> > >> > 1) Park Mode ('cfg->park'): In Park mode, engine will park on frame >> > referenced by >> > 'cfg->park_frm', so user will have control on each frame in this mode. >> > >> > 2) Interrupt Coalesce ('cfg->coalesce'): Used for setting interrupt >> > threshold. This value >> > determines the number of frame buffers to process. To use this feature, >> > 'cfg->frm_cnt_en' should be set. >> > >> > 3) Frame Synchronization Source ('cfg->ext_fsync'): Can be an >> > external/internal frame >> > synchronization source. Used to synchronize one channel (MM2S/S2MM) with >> > another (S2MM/MM2S) channel. >> > >> > 4) Genlock Synchronization ('cfg->genlock'): Used to avoid mismatch rate between >> > master and slave. In master mode (cfg->master), frames are not dropped and >> > slave can drop frames to adjust to master frame rate. >> > >> > And in future, this Engine being a soft IP, we could expect some more additional >> > parameters. Isn't a good idea to have a private member in dma_slave_config for >> > sharing additional configuration between slave device and dma engine? Or a new >> > dma_ctrl_cmd like FSLDMA_EXTERNAL_START? > > The idea of a generic API is that we can use it for most of the controllers. Even > if you are planning to support a family of controllers > > ATM, lets not discuss the possiblity of private member and try to exhanust all > possible options. Worst case you can embed the dma_slave_config in > xilinx_dma_slave_config and retrieve it in dmac driver Ok. Srikanth > > -- > ~Vinod > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/