mpb27 / xilinx-dma

Forking the Xilinx DMA driver to improve its capabilities.

#xilinx-dma Forking the Xilinx DMA driver to improve its capabilities.

Original link : Xilinx GitHub

Note : The forked version was choosen as the last version before the merge of the DMA, VDMA, and CDMA driver into one.

Primary goal of this project:

• To add the abliity to retrieve the actual DMA transfer size after each DMA transaction.

Other goals of this project are:

• To document the operation of this driver.
• To improve the comments in the code.

xilinx-dma's Issues

Spin lock inside IRQ should use IRQ variant.

Rewrite the below lines to use spin_lock_irqsave and spin_unlock_irqrestore.

xilinx-dma/xilinx-dma-dr/xilinx_dma_dr.c

Lines 706 to 709 in fe65c9a

	spin_lock(&chan->lock);
	xilinx_dma_complete_active_irq(chan);
	xilinx_dma_start_transfer_irq(chan);
	spin_unlock(&chan->lock);

Replace spin_lock with spin_lock_bh in axis_reader.c.

We can use a spin_lock_bh in axis_reader.c if we can guarantee that the callback is never executed in an interrupt context. The proper locking between user context and a tasklet is a spin_lock_bh.

Reference:

1. https://mirrors.edge.kernel.org/pub/linux/kernel/people/rusty/kernel-locking/c214.html
2. https://www.kernel.org/doc/html/v4.15/kernel-hacking/locking.html#cheat-sheet-for-locking

Rewrite xilinx_dma_dr to use a workqueue instead of a tasklet.

Tasklets are being removed and a work queue should be sufficient to proces the DMA completion callback.

Reference:

1. https://lwn.net/Articles/239230/

Callback should be set to NULL before IRQ release.

The IRQ handler might not be re-entrent but it is still probably a good idea to set the callback to NULL earlier, before re-enabling interrupts.

xilinx-dma/xilinx-dma-dr/xilinx_dma_dr.c

Lines 532 to 539 in fe65c9a

	if (desc->async_tx.callback) {
	dma_async_tx_callback callback = desc->async_tx.callback;
	spin_unlock_irqrestore(&chan->lock, flags);
	callback(desc->async_tx.callback_param);
	spin_lock_irqsave(&chan->lock, flags);
	desc->async_tx.callback = NULL;