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spi: fsl-espi: make better use of the RX FIFO

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So far an interrupt is triggered whenever there's at least one byte
in the RX FIFO. This results in a unnecessarily high number of
interrupts.
Change this to generate an interrupt if
- RX FIFO is half full (except if all bytes to read fit into the
  RX FIFO anyway)
- end of transfer has been reached

This way the number of interrupts can be significantly reduced.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Heiner Kallweit 2016-10-27 21:27:56 +02:00 committed by Mark Brown
parent db1b049fad
commit e508cea45b
1 changed files with 8 additions and 3 deletions
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11
drivers/spi/spi-fsl-espi.c
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@ -55,9 +55,10 @@
#define CSMODE_CG(x) ((x) << 3)
#define FSL_ESPI_FIFO_SIZE 32
#define FSL_ESPI_RXTHR 15
/* Default mode/csmode for eSPI controller */
#define SPMODE_INIT_VAL (SPMODE_TXTHR(4) | SPMODE_RXTHR(3))
#define SPMODE_INIT_VAL (SPMODE_TXTHR(4) | SPMODE_RXTHR(FSL_ESPI_RXTHR))
#define CSMODE_INIT_VAL (CSMODE_POL_1 | CSMODE_BEF(0) \
| CSMODE_AFT(0) | CSMODE_CG(1))
@ -263,6 +264,7 @@ static void fsl_espi_setup_transfer(struct spi_device *spi,
static int fsl_espi_bufs(struct spi_device *spi, struct spi_transfer *t)
{
struct mpc8xxx_spi *mpc8xxx_spi = spi_master_get_devdata(spi->master);
u32 mask;
int ret;
mpc8xxx_spi->rx_len = t->len;
@ -277,8 +279,11 @@ static int fsl_espi_bufs(struct spi_device *spi, struct spi_transfer *t)
fsl_espi_write_reg(mpc8xxx_spi, ESPI_SPCOM,
(SPCOM_CS(spi->chip_select) | SPCOM_TRANLEN(t->len - 1)));
/* enable rx ints */
fsl_espi_write_reg(mpc8xxx_spi, ESPI_SPIM, SPIM_RNE);
/* enable interrupts */
mask = SPIM_DON;
if (mpc8xxx_spi->rx_len > FSL_ESPI_FIFO_SIZE)
mask |= SPIM_RXT;
fsl_espi_write_reg(mpc8xxx_spi, ESPI_SPIM, mask);
/* Prevent filling the fifo from getting interrupted */
spin_lock_irq(&mpc8xxx_spi->lock);