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Unverified Commit cbaa62e0 authored by David Lechner's avatar David Lechner Committed by Mark Brown
Browse files

spi: add software implementation for SPI_CS_WORD 



This adds a default software implementation for the SPI_CS_WORD flag for
controllers that don't have such a feature.

The SPI_CS_WORD flag indicates that the CS line should be toggled
between each word sent, not just between each transfer. The
implementation works by using existing functions to split transfers into
one-word-sized transfers and sets the cs_change bit for each of the
new transfers.

Signed-off-by: default avatarDavid Lechner <david@lechnology.com>
Acked-by: default avatarJonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent 0baf9eb2

drivers/spi/spi.c

+30 −1
Original line number Diff line number Diff line
@@ -2774,8 +2774,10 @@ int spi_setup(struct spi_device *spi) 
		return -EINVAL;

	/* help drivers fail *cleanly* when they need options

	 * that aren't supported with their current controller

	 * SPI_CS_WORD has a fallback software implementation,

	 * so it is ignored here.

	 */

	bad_bits = spi->mode & ~spi->controller->mode_bits;

	bad_bits = spi->mode & ~(spi->controller->mode_bits | SPI_CS_WORD);

	ugly_bits = bad_bits &

		    (SPI_TX_DUAL | SPI_TX_QUAD | SPI_RX_DUAL | SPI_RX_QUAD);

	if (ugly_bits) {
@@ -2829,6 +2831,33 @@ static int __spi_validate(struct spi_device *spi, struct spi_message *message) 
	if (list_empty(&message->transfers))

		return -EINVAL;



	/* If an SPI controller does not support toggling the CS line on each

	 * transfer (indicated by the SPI_CS_WORD flag), we can emulate it by

	 * splitting transfers into one-word transfers and ensuring that

	 * cs_change is set for each transfer.

	 */

	if ((spi->mode & SPI_CS_WORD) && !(ctlr->mode_bits & SPI_CS_WORD)) {

		size_t maxsize;

		int ret;



		maxsize = (spi->bits_per_word + 7) / 8;



		/* spi_split_transfers_maxsize() requires message->spi */

		message->spi = spi;



		ret = spi_split_transfers_maxsize(ctlr, message, maxsize,

						  GFP_KERNEL);

		if (ret)

			return ret;



		list_for_each_entry(xfer, &message->transfers, transfer_list) {

			/* don't change cs_change on the last entry in the list */

			if (list_is_last(&xfer->transfer_list, &message->transfers))

				break;

			xfer->cs_change = 1;

		}

	}



	/* Half-duplex links include original MicroWire, and ones with

	 * only one data pin like SPI_3WIRE (switches direction) or where

	 * either MOSI or MISO is missing.  They can also be caused by