Unverified Commit 26751de2 authored by Robin Murphy's avatar Robin Murphy Committed by Mark Brown
Browse files

spi: bcm2835: Micro-optimise FIFO loops 



The blind and counted loops are always called with nonzero count, so
convert them to do-while loops that lead to slightly more efficient
code generation. With GCC 8.3 this shaves off 1-2 instructions per
iteration in each case.

Signed-off-by: default avatarRobin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/9242863077acf9a64e4b3720e479855b88d19e82.1592261248.git.robin.murphy@arm.com


Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent afe7e363

drivers/spi/spi-bcm2835.c

+8 −10
Original line number Diff line number Diff line
@@ -245,13 +245,13 @@ static inline void bcm2835_rd_fifo_count(struct bcm2835_spi *bs, int count) 


	bs->rx_len -= count;



	while (count > 0) {

	do {

		val = bcm2835_rd(bs, BCM2835_SPI_FIFO);

		len = min(count, 4);

		memcpy(bs->rx_buf, &val, len);

		bs->rx_buf += len;

		count -= 4;

	}

	} while (count > 0);

}



/**
@@ -271,7 +271,7 @@ static inline void bcm2835_wr_fifo_count(struct bcm2835_spi *bs, int count) 


	bs->tx_len -= count;



	while (count > 0) {

	do {

		if (bs->tx_buf) {

			len = min(count, 4);

			memcpy(&val, bs->tx_buf, len);
@@ -281,7 +281,7 @@ static inline void bcm2835_wr_fifo_count(struct bcm2835_spi *bs, int count) 
		}

		bcm2835_wr(bs, BCM2835_SPI_FIFO, val);

		count -= 4;

	}

	} while (count > 0);

}



/**
@@ -310,12 +310,11 @@ static inline void bcm2835_rd_fifo_blind(struct bcm2835_spi *bs, int count) 
	count = min(count, bs->rx_len);

	bs->rx_len -= count;



	while (count) {

	do {

		val = bcm2835_rd(bs, BCM2835_SPI_FIFO);

		if (bs->rx_buf)

			*bs->rx_buf++ = val;

		count--;

	}

	} while (--count);

}



/**
@@ -330,11 +329,10 @@ static inline void bcm2835_wr_fifo_blind(struct bcm2835_spi *bs, int count) 
	count = min(count, bs->tx_len);

	bs->tx_len -= count;



	while (count) {

	do {

		val = bs->tx_buf ? *bs->tx_buf++ : 0;

		bcm2835_wr(bs, BCM2835_SPI_FIFO, val);

		count--;

	}

	} while (--count);

}



static void bcm2835_spi_reset_hw(struct bcm2835_spi *bs)

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