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Commit e3a2be30 authored by Martin Sperl's avatar Martin Sperl Committed by Mark Brown
Browse files

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: default avatarMartin Sperl <kernel@martin.sperl.org>
Tested-by: default avatarMartin Sperl <kernel@martin.sperl.org>
Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent 1e4df62d

drivers/spi/spi-bcm2835.c

+16 −0
Original line number Diff line number Diff line
@@ -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