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spi: bcm2835: Micro-optimise FIFO loops

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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: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/9242863077acf9a64e4b3720e479855b88d19e82.1592261248.git.robin.murphy@arm.com
Signed-off-by: Mark Brown <broonie@kernel.org>
This commit is contained in:
Robin Murphy 2020-06-16 01:09:29 +01:00 • committed by Mark Brown
parent afe7e36360
commit 26751de25d
No known key found for this signature in database
GPG key ID: 24D68B725D5487D0
1 changed files with 8 additions and 10 deletions
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18
drivers/spi/spi-bcm2835.c
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@ -245,13 +245,13 @@ static inline void bcm2835_rd_fifo_count(struct bcm2835_spi *bs, int count)
bs->rx_len -= count; bs->rx_len -= count;
while (count > 0) { do {
val = bcm2835_rd(bs, BCM2835_SPI_FIFO); val = bcm2835_rd(bs, BCM2835_SPI_FIFO);
len = min(count, 4); len = min(count, 4);
memcpy(bs->rx_buf, &val, len); memcpy(bs->rx_buf, &val, len);
bs->rx_buf += len; bs->rx_buf += len;
count -= 4; 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; bs->tx_len -= count;
while (count > 0) { do {
if (bs->tx_buf) { if (bs->tx_buf) {
len = min(count, 4); len = min(count, 4);
memcpy(&val, bs->tx_buf, len); 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); bcm2835_wr(bs, BCM2835_SPI_FIFO, val);
count -= 4; 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); count = min(count, bs->rx_len);
bs->rx_len -= count; bs->rx_len -= count;
while (count) { do {
val = bcm2835_rd(bs, BCM2835_SPI_FIFO); val = bcm2835_rd(bs, BCM2835_SPI_FIFO);
if (bs->rx_buf) if (bs->rx_buf)
*bs->rx_buf++ = val; *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); count = min(count, bs->tx_len);
bs->tx_len -= count; bs->tx_len -= count;
while (count) { do {
val = bs->tx_buf ? *bs->tx_buf++ : 0; val = bs->tx_buf ? *bs->tx_buf++ : 0;
bcm2835_wr(bs, BCM2835_SPI_FIFO, val); bcm2835_wr(bs, BCM2835_SPI_FIFO, val);
count--; } while (--count);
}
} }
static void bcm2835_spi_reset_hw(struct bcm2835_spi *bs) static void bcm2835_spi_reset_hw(struct bcm2835_spi *bs)