From e3a2be3030e2fec27a2577d3c52203da090a4366 Mon Sep 17 00:00:00 2001 From: Martin Sperl Date: Sun, 29 Mar 2015 16:03:25 +0200 Subject: [PATCH] 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 Tested-by: Martin Sperl Signed-off-by: Mark Brown --- drivers/spi/spi-bcm2835.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) 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 -- 2.20.1