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SubjectRe: [PATCH v5] dma: Add Xilinx AXI Direct Memory Access Engine driver support
On Mon, Mar 23, 2015 at 04:24:26PM +0000, Appana Durga Kedareswara Rao wrote:
> > > +static enum dma_status xilinx_dma_tx_status(struct dma_chan *dchan,
> > > + dma_cookie_t cookie,
> > > + struct dma_tx_state *txstate) {
> > > + struct xilinx_dma_chan *chan = to_xilinx_chan(dchan);
> > > + enum dma_status ret;
> > > + unsigned long flags;
> > > +
> > > + ret = dma_cookie_status(dchan, cookie, txstate);
> > > + if (ret != DMA_COMPLETE) {
> > txstate can be null
>
> Ok will modify.
> It will be something like below
>
> ret = dma_cookie_status(dchan, cookie, txstate);
> if (ret == DMA_COMPLETE || !txstate)
> return ret;
> Calculate residue.
>
> Please correct me if I am wrong
Thats right

> > > +static void xilinx_dma_complete_descriptor(struct xilinx_dma_chan
> > > +*chan) {
> > > + struct xilinx_dma_tx_descriptor *desc;
> > > + struct xilinx_dma_tx_segment *segment, *next;
> > > + struct xilinx_dma_desc_hw *hw;
> > > + unsigned long flags;
> > > + u32 residue = 0;
> > > +
> > > + spin_lock_irqsave(&chan->lock, flags);
> > > +
> > > + desc = chan->active_desc;
> > > + if (!desc) {
> > > + dev_dbg(chan->dev, "no running descriptors\n");
> > > + goto out_unlock;
> > > + }
> > > +
> > > + if (chan->has_sg) {
> > > + list_for_each_entry_safe(segment, next, &desc->segments,
> > node) {
> > > + hw = &segment->hw;
> > > + residue += (hw->control - hw->status) &
> > > + XILINX_DMA_MAX_TRANS_LEN;
> > > + }
> > why are we calculating residue here?
>
>
> This API is called from Interrupt handler when the BD(Buffer Descriptor) is
> Successfully transmitted.
> Thought of calculating residue here is more accurate than calculating the residue in the
> tx_status.
Nope, you need to report reside when asked not precompute!

> This is while preparing the descs, but I see your point. I will fix
> it in my next version of the patch.
>
> >
> > > + async_tx_ack(&desc->async_tx);
> > why?
>
> It is not required?
> As far as I know we should ack the descriptor for Slave dma case right?
> ( https://www.kernel.org/doc/Documentation/crypto/async-tx-api.txt )
No you dont, for slave you need to read Documentation/dmaengine/

> > > +static int xilinx_dma_remove(struct platform_device *pdev) {
> > > + struct xilinx_dma_device *xdev = platform_get_drvdata(pdev);
> > > + int i;
> > > +
> > > + of_dma_controller_free(pdev->dev.of_node);
> > > + dma_async_device_unregister(&xdev->common);
> > > +
> > > + for (i = 0; i < XILINX_DMA_MAX_CHANS_PER_DEVICE; i++)
> > > + if (xdev->chan[i])
> > > + xilinx_dma_chan_remove(xdev->chan[i]);
> > > +
> > at this point your irq is active and tasklet cna still be scheduled
>
> We are freeing the IRQ and killing the tasklet in the chan_remove API why irq is still active at this point of time?
I missed this bit, if you are freeing irq explcitly then it should be okay

> I didn't get you.
> Could you please explain a bit?

--
~Vinod



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