linux-kernel - [PATCH 3/3] spi: spi-geni-qcom: Slightly optimize setup of bidirectional xfters

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Date:   Sat, 12 Sep 2020 14:08:01 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     Akash Asthana <akashast@...eaurora.org>, swboyd@...omium.org,
        Douglas Anderson <dianders@...omium.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-spi@...r.kernel.org
Subject: [PATCH 3/3] spi: spi-geni-qcom: Slightly optimize setup of bidirectional xfters

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@...omium.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