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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: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Rasmus Villemoes 2019-03-27 14:30:52 +00:00 committed by Mark Brown
parent a798a7086c
commit af0e624290
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1 changed files with 16 additions and 0 deletions
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16
drivers/spi/spi-fsl-spi.c
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@ -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) {