From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vinod Koul Subject: Re: [PATCH v3 2/2] dma: Add Xilinx AXI Direct Memory Access Engine driver support Date: Tue, 9 Sep 2014 21:27:16 +0530 Message-ID: <20140909155716.GN1610@intel.com> References: <1406549869-24422-1-git-send-email-sthokal@xilinx.com> <1406549869-24422-2-git-send-email-sthokal@xilinx.com> <20140819170346.GS13288@intel.com> <20140904063613.GD1610@intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Srikanth Thokala Cc: devicetree@vger.kernel.org, Levente Kurusa , Jassi Brar , svemula@xilinx.com, Michal Simek , "linux-kernel@vger.kernel.org" , dmaengine@vger.kernel.org, Rob Herring , anirudh@xilinx.com, Grant Likely , "Williams, Dan J" , "linux-arm-kernel@lists.infradead.org" List-Id: devicetree@vger.kernel.org On Tue, Sep 09, 2014 at 12:52:16AM +0530, Srikanth Thokala wrote: > Hi Vinod, > > On Thu, Sep 4, 2014 at 12:06 PM, Vinod Koul wrote: > > On Wed, Sep 03, 2014 at 12:17:43PM +0530, Srikanth Thokala wrote: > >> Hi Vinod, > >> > >> Apologies for the delay. > >> > >> On Tue, Aug 19, 2014 at 10:33 PM, Vinod Koul wrote: > >> > On Mon, Jul 28, 2014 at 05:47:49PM +0530, Srikanth Thokala wrote: > >> >> +struct xilinx_dma_chan { > >> >> + struct xilinx_dma_device *xdev; > >> >> + u32 ctrl_offset; > >> >> + spinlock_t lock; > >> >> + struct list_head pending_list; > >> >> + struct xilinx_dma_tx_descriptor *active_desc; > >> >> + struct xilinx_dma_tx_descriptor *allocated_desc; > >> >> + struct list_head done_list; > >> >> + struct list_head free_seg_list; > >> >> + struct dma_chan common; > >> >> + struct xilinx_dma_tx_segment *seg_v; > >> >> + dma_addr_t seg_p; > >> >> + struct device *dev; > >> >> + int irq; > >> >> + int id; > >> >> + enum dma_transfer_direction direction; > >> > This looks suspect. Why should channel have direction, for a descriptor it > >> > makes sense though. > >> > >> The channel only supports transfers in one direction. Either from memory to > >> peripheral or from peripheral to memory, that's fixed and can't be changed > >> at runtime. So, the driver needs to know which direction the channel supports > >> and hence it can reject transfers with the wrong direction. > > But you already have this information in descriptor so why duplicate? > > Our descriptor doesn't have the information of channel direction, we have this > information only in the chan structure (struct xilinx_dma_chan) which > is populated > while parsing the DT. So, we use this information to ensure if we are servicing > proper channel (in prep_slave_sg call). One of the argument of prep_slave_sg call is direction. You need to use that and store in in your descriptor for using it afterwards > FYI: We also need the direction of the channel so that we can select SRC/DST > register address in the issue_pending() call. And you have the descriptor there as well so can use it -- ~Vinod