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Subject[PATCH 3/3] spi: spi-geni-qcom: Slightly optimize setup of bidirectional xfters
Date
When setting up a bidirectional transfer we need to program both the
TX and RX lengths. We don't need a memory barrier between those two
writes. Factor out the __iowmb() and use writel_relaxed(). This
saves a fraction of a microsecond of setup overhead on bidirectional
transfers.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
---

drivers/spi/spi-geni-qcom.c | 13 ++++++++++---
1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/spi-geni-qcom.c b/drivers/spi/spi-geni-qcom.c
index 92d88bf85a90..6c7e12b68bf0 100644
--- a/drivers/spi/spi-geni-qcom.c
+++ b/drivers/spi/spi-geni-qcom.c
@@ -376,15 +376,22 @@ static void setup_fifo_xfer(struct spi_transfer *xfer,
len &= TRANS_LEN_MSK;

mas->cur_xfer = xfer;
+
+ /*
+ * Factor out the __iowmb() so that we can use writel_relaxed() for
+ * both writes below and thus only incur the overhead once even if
+ * we execute both of them.
+ */
+ __iowmb();
+
if (xfer->tx_buf) {
m_cmd |= SPI_TX_ONLY;
mas->tx_rem_bytes = xfer->len;
- writel(len, se->base + SE_SPI_TX_TRANS_LEN);
+ writel_relaxed(len, se->base + SE_SPI_TX_TRANS_LEN);
}
-
if (xfer->rx_buf) {
m_cmd |= SPI_RX_ONLY;
- writel(len, se->base + SE_SPI_RX_TRANS_LEN);
+ writel_relaxed(len, se->base + SE_SPI_RX_TRANS_LEN);
mas->rx_rem_bytes = xfer->len;
}

--
2.28.0.618.gf4bc123cb7-goog
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