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| author | Martin Sperl <kernel@martin.sperl.org> | 2015-03-29 16:03:25 +0200 |
|---|---|---|
| committer | Mark Brown <broonie@kernel.org> | 2015-03-29 09:53:30 -0700 |
| commit | e3a2be3030e2fec27a2577d3c52203da090a4366 (patch) | |
| tree | 91d1180ee0742a9403c2448cd1ceb5d1d967653c /drivers/spi/spi-bcm2835.c | |
| parent | 1e4df62d46fa45109123f2b265b2d8146031db16 (diff) | |
| download | lwn-e3a2be3030e2fec27a2577d3c52203da090a4366.tar.gz lwn-e3a2be3030e2fec27a2577d3c52203da090a4366.zip | |
spi: bcm2835: fill FIFO before enabling interrupts to reduce interrupts/message
To reduce the number of interrupts/message we fill the FIFO before
enabling interrupts - for short messages this reduces the interrupt count
from 2 to 1 interrupt.
There have been rare cases where short (<200ns) chip-select switches with
native CS have been observed during such operation, this is why this
optimization is only enabled for GPIO-CS.
Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
Tested-by: Martin Sperl <kernel@martin.sperl.org>
Signed-off-by: Mark Brown <broonie@kernel.org>
Diffstat (limited to 'drivers/spi/spi-bcm2835.c')
| -rw-r--r-- | drivers/spi/spi-bcm2835.c | 16 |
1 files changed, 16 insertions, 0 deletions
diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c index 2e6533e34b19..08e5406c5029 100644 --- a/drivers/spi/spi-bcm2835.c +++ b/drivers/spi/spi-bcm2835.c @@ -203,6 +203,22 @@ static int bcm2835_spi_transfer_one(struct spi_master *master, bs->tx_len = tfr->len; bs->rx_len = tfr->len; + /* fill in fifo if we have gpio-cs + * note that there have been rare events where the native-CS + * flapped for <1us which may change the behaviour + * with gpio-cs this does not happen, so it is implemented + * only for this case + */ + if (gpio_is_valid(spi->cs_gpio)) { + /* enable HW block, but without interrupts enabled + * this would triggern an immediate interrupt + */ + bcm2835_wr(bs, BCM2835_SPI_CS, + cs | BCM2835_SPI_CS_TA); + /* fill in tx fifo as much as possible */ + bcm2835_wr_fifo(bs); + } + /* * Enable the HW block. This will immediately trigger a DONE (TX * empty) interrupt, upon which we will fill the TX FIFO with the |