i.MX8M FlexSPI DMA callback never called

[alvaro_tx]

Hi, 

We are developing a solution using FlexSPI to read some values from a FPGA and we are having issues with the FlexSPI driver when running DMA. 

This issue is reproduced in i.MX8M Mini and Plus.

So far we managed to:

1. Initialize the DMA channels for FlexSPI (SDMA1, channels 36 and 37). 

&flexspi {
	status = "okay";
	pinctrl-names = "default";
	pinctrl-0 = <&pinctrl_flexspi0>;
	dmas = <&sdma1 36 8 2>, <&sdma1 37 8 1>;
	dma-names = "tx", "rx";
	fpga0: fpga@0 {
		reg = <0>;
		#address-cells = <1>;
		#size-cells = <1>;
		compatible = "fpga,fspi";
		spi-max-frequency = <100000>;
		spi-tx-bus-width = <4>;
		spi-rx-bus-width = <4>;
	};

(dma_request_slave_channel_reason , dma_alloc_coherent and dmaengine_slave_config all returned OK) 

Our DMA channel config: 

cfg.src_addr = (phys_addr_t)(f->iobase + FSPI_RFDR);
	cfg.src_addr_width = DMA_SLAVE_BUSWIDTH_4_BYTES;
	cfg.src_maxburst = 2;
	cfg.direction = DMA_DEV_TO_MEM;

2. Use the IP mode for FlexSPI without DMA without issues.

So, we are modifying the spi-nxp-fspi driver and trying to get DMA + IP mode working. 

IPRXFCR:

• IPRXFCR_DMA_EN set.
• IPRXFCR_CLR set (for clearing RX FIFO)
• Write 1 with IPRXFCR_WMRK (This one we are not too sure)
• Run the DMA submit

However, we always get a DMA timeout. Here is the snippet of the DMA request (based on spi-fsl-dspi.c) :

static int fspi_next_xfer_dma_submit(struct nxp_fspi *f)
{
	struct device *dev = f->dev;
	struct nxp_fspi_dma *dma = f->dma;

	dma->rx_desc = dmaengine_prep_slave_single(dma->chan_rx,
					dma->rx_dma_phys,
					dma->curr_xfer_len *
					DMA_SLAVE_BUSWIDTH_4_BYTES,
					DMA_DEV_TO_MEM,
					DMA_PREP_INTERRUPT | DMA_CTRL_ACK);
	if (!dma->rx_desc) {
		dev_err(dev, "Not able to get desc for DMA xfer\n");
		return -EIO;
	}

	dma->rx_desc->callback = fspi_rx_dma_callback;
	dma->rx_desc->callback_param = f;
	if (dma_submit_error(dmaengine_submit(dma->rx_desc))) {
		dev_err(dev, "DMA submit failed\n");
		return -EINVAL;
	}

	reinit_completion(&f->dma->cmd_rx_complete);

	dma_async_issue_pending(dma->chan_rx);

	return 0;
}

Here are the status of the related registers after failing the transfer (in hex):

IPRXFCR: 0002
(RXDMAEN 1)

INTR: 0060
(IPTXWE 1 IPRXWA 1)

INTEN: 0001
(IPCMDGE 1)

We are testing this with the interface we made to test the driver that creates a device in /dev/. This sample program simply tries to read the RX FIFO buffer with a dd read operation to this created device. We should get some stored data (or 0s) but we are always getting a DMA RX timeout. 

Any idea? We think that we are probably not setting the watermark levels correctly but don't really know what we should set them to. Thanks. 

EDIT: We found out that the problem is the callback (fspi_rx_dma_callback) is never being called. However, we don't know why.... 

[AldoG]

Hello,

In Linux FlexSPI driver do not have DMA support.

Best regards,
Aldo.

[alvaro_tx]

Hi Aldo, yes, we know that it doesn't have it, that is why we are trying to add it from our side (hence the question with the implementation).

Alvaro. 

[festevam]

Hi @alvaro_tx 

Have you managed to implement FlexSPI DMA support? 

If so, could you please share your patch?

Thanks

[alvaro_tx]

Unfortunately no. We ended up using FlexSPI without DMA.