Re: [PATCH] spi: spi-bcm2835.c: Fix 3-wire mode

[Lukas Wunner]

On Mon, Jul 01, 2019 at 07:24:23AM +0000, Sa, Nuno wrote:
> The problem is in spi_map_msg() which
> allocates dummy buffers (because of the ctrl flags). As a result, in
> bcm2835_spi_transfer_one() we set "cs |= BCM2835_SPI_CS_REN;" when we
> want to do tx only. I believe this was the actual problem...

I see.  In that case, try:

 	/* handle all the 3-wire mode */
-	if ((spi->mode & SPI_3WIRE) && (tfr->rx_buf))
+	if ((spi->mode & SPI_3WIRE) && (tfr->rx_buf != ctlr->dummy_rx))
 		cs |= BCM2835_SPI_CS_REN;
 	else
 		cs &= ~BCM2835_SPI_CS_REN;

Use master->dummy_rx instead of ctlr->dummy_rx prior to commit
5f336ea53b6b ("spi: bcm2835: Replace spi_master by spi_controller").

This could be something that users of your cape might use on older
kernels in lieu of my upcoming patch set to drop MUST_RX / MUST_TX.

Thanks,

Lukas