DMA-enabled SPI in peripheral (slave) mode hangs in ll_func_spi_dma_busy on STM32U585

[rob-zeno]

Hi.

I'm trying to use DMA-enabled SPI on an STM32U585 in peripheral (i.e., slave) mode.

The code works in non-DMA mode (i.e., I don't enable CONFIG_SPI_STM32_DMA, and I don't enable gpdma1 and don't add dmas in my overlay file).

But when I enable DMA, I get a hang inside "transceive_dma" in "ll_func_spi_dma_busy" (which just calls "LL_SPI_IsActiveFlag_TXC", which just checks the status of the SPI_SR_TXC bit). Basically, the SPI_SR_TXC appears to be "stuck" in a busy state (zero, according to reference manual -- it goes to 1 when done).

Interestingly enough, there's an errata for a SIMILAR problem on earlier silicon (this is an STM32 U5 series, which uses the H7-series SPI implementation).

CONFIG_SPI_STM32_ERRATA_BUSY is not allowed (i.e., I can't enable it in my conf file) for the STM32 U5 series, but if I modify the spi_ll_stm32.c file to force it to be defined:

	#define CONFIG_SPI_STM32_ERRATA_BUSY
	#define CONFIG_SPI_STM32_BUSY_FLAG_TIMEOUT  100000

Then the code "works" although it seems like it has a performance impact on my system (the SPI I/O thread is a cooperative thread).

But I haven't seen ANY information that indicates this should be necessary on this version of silicon?

This is on a custom board, and unfortunately, the SPI pins are not exposed so getting a logic analyzer trace is not really in the works for someone with my skill.

The relevant portions of my overlay are:

&gpdma1 {
	status = "okay";
};

&spi2 {
	pinctrl-0 = <&spi2_sck_pb10 &spi2_miso_pc2 &spi2_mosi_pc1>;
	pinctrl-names = "default";
	status = "okay";
	
	dmas = <&gpdma1 0 9 ( STM32_DMA_PRIORITY_HIGH | STM32_DMA_PERIPH_TX )
			&gpdma1 1 8 ( STM32_DMA_PRIORITY_HIGH | STM32_DMA_PERIPH_RX )>;
	dma-names = "tx", "rx";

	fifo-enable;
};

A final note -- there's no use of CS. It's controlled by the master anyway, but in my case, this is the only peripheral on this SPI bus. I call "transceive_dma", and it starts the DMA operation, and because it's in peripheral mode, "wait_dma_rx_tx_done" will sleep forever until the DMA interrupt fires.