spi: spi-fsl-spi: automatically adapt bits-per-word in cpu mode (af0e6242) · Commits · 戴 / test

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:

Rasmus Villemoes <rasmus.villemoes@prevas.dk> Signed-off-by:

Mark Brown <broonie@kernel.org>

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) {

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