Hi Vinod, > -----Original Message----- > From: Vinod Koul [mailto:[email protected]] > Sent: Wednesday, April 11, 2018 2:39 PM > To: Radhey Shyam Pandey <[email protected]> > Cc: [email protected]; [email protected]; Appana Durga > Kedareswara Rao <[email protected]>; Radhey Shyam Pandey > <[email protected]>; [email protected]; [email protected]; > [email protected]; [email protected] > Subject: Re: [RFC 2/6] dmaengine: xilinx_dma: Pass AXI4-Stream control > words to netdev dma client > > On Mon, Apr 02, 2018 at 04:09:02PM +0530, Radhey Shyam Pandey wrote: > > > + > > + if (chan->xdev->has_axieth_connected) { > > + seg = list_first_entry(&desc->segments, > > + struct xilinx_axidma_tx_segment, > node); > > + if (cb.callback_param) { > > + app_w = (u32 *) cb.callback_param; > > why are you interpreting callback_param? This is plainly wrong. > we do not know what is the interpretation of callback_param and it is > internal to submitter. In design, if AXI DMA is connected to AXI Ethernet IP there are certain AXI4-Stream Status fields (RX) that we need to pass to ethernet driver along with data buffer. An example includes: checksum fields, packet length etc. To pass these control words there is a structure defined between dmaengine and client. Before calling the client callback stream control words are copied to dma client callback_param struct (only if axieth is connected).
I understand it's not an ideal way and we shouldn't be interpreting callback_param but couldn't find any better alternative of passing custom information from dmaengine to client driver and still be aligned to the framework. > > What exactly is the problem you are trying to solve? As mentioned above we need to pass AXI4-stream words(custom data) from dmaengine driver to dma client driver(ethernet) for each DMA descriptor. Current solution populates callback_param struct (only if axieth is connected). Please let me know if there is an alternate solution. > > > + hw = &seg->hw; > > + *app_w = hw->status & > XILINX_DMA_MAX_TRANS_LEN; > > + memcpy(app_w, hw->app, sizeof(u32) * > > + XILINX_DMA_NUM_APP_WORDS); > > + } > > -- > ~Vinod
