Donate to e Foundation | Murena handsets with /e/OS | Own a part of Murena! Learn more

Unverified Commit af0e6242 authored by Rasmus Villemoes's avatar Rasmus Villemoes Committed by Mark Brown
Browse files

spi: spi-fsl-spi: automatically adapt bits-per-word in cpu mode 



Taking one interrupt for every byte is rather slow. Since the
controller is perfectly capable of transmitting 32 bits at a time,
change t->bits_per-word to 32 when the length is divisible by 4 and
large enough that the reduced number of interrupts easily compensates
for the one or two extra fsl_spi_setup_transfer() calls this causes.

Signed-off-by: default avatarRasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent a798a708

drivers/spi/spi-fsl-spi.c

+16 −0
Original line number Diff line number Diff line
@@ -363,12 +363,28 @@ static int fsl_spi_bufs(struct spi_device *spi, struct spi_transfer *t, 
static int fsl_spi_do_one_msg(struct spi_master *master,

			      struct spi_message *m)

{

	struct mpc8xxx_spi *mpc8xxx_spi = spi_master_get_devdata(master);

	struct spi_device *spi = m->spi;

	struct spi_transfer *t, *first;

	unsigned int cs_change;

	const int nsecs = 50;

	int status, last_bpw;



	/*

	 * In CPU mode, optimize large byte transfers to use larger

	 * bits_per_word values to reduce number of interrupts taken.

	 */

	if (!(mpc8xxx_spi->flags & SPI_CPM_MODE)) {

		list_for_each_entry(t, &m->transfers, transfer_list) {

			if (t->len < 256 || t->bits_per_word != 8)

				continue;

			if ((t->len & 3) == 0)

				t->bits_per_word = 32;

			else if ((t->len & 1) == 0)

				t->bits_per_word = 16;

		}

	}



	/* Don't allow changes if CS is active */

	cs_change = 1;

	list_for_each_entry(t, &m->transfers, transfer_list) {