linux-kernel - [PATCH 2/3] spi: spi-geni-qcom: Don't program CS

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Date:   Sat, 12 Sep 2020 14:08:00 -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 2/3] spi: spi-geni-qcom: Don't program CS_TOGGLE again and again

We always toggle the chip select manually in spi-geni-qcom so that we
can properly implement the Linux API.  There's no reason to program
this to the hardware on every transfer.  Program it once at init and
be done with it.

This saves some part of a microsecond of overhead on each transfer.
While not really noticeable on any real world benchmarks, we might as
well save the time.

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

 drivers/spi/spi-geni-qcom.c | 12 +++++++-----
 1 file changed, 7 insertions(+), 5 deletions(-)

diff --git a/drivers/spi/spi-geni-qcom.c b/drivers/spi/spi-geni-qcom.c
index 7f0bf0dec466..92d88bf85a90 100644
--- a/drivers/spi/spi-geni-qcom.c
+++ b/drivers/spi/spi-geni-qcom.c
@@ -290,6 +290,7 @@ static int spi_geni_init(struct spi_geni_master *mas)
 {
 	struct geni_se *se = &mas->se;
 	unsigned int proto, major, minor, ver;
+	u32 spi_tx_cfg;
 
 	pm_runtime_get_sync(mas->dev);
 
@@ -322,6 +323,11 @@ static int spi_geni_init(struct spi_geni_master *mas)
 
 	geni_se_select_mode(se, GENI_SE_FIFO);
 
+	/* We always control CS manually */
+	spi_tx_cfg = readl(se->base + SE_SPI_TRANS_CFG);
+	spi_tx_cfg &= ~CS_TOGGLE;
+	writel(spi_tx_cfg, se->base + SE_SPI_TRANS_CFG);
+
 	pm_runtime_put(mas->dev);
 	return 0;
 }
@@ -331,7 +337,7 @@ static void setup_fifo_xfer(struct spi_transfer *xfer,
 				u16 mode, struct spi_master *spi)
 {
 	u32 m_cmd = 0;
-	u32 spi_tx_cfg, len;
+	u32 len;
 	struct geni_se *se = &mas->se;
 	int ret;
 
@@ -350,7 +356,6 @@ static void setup_fifo_xfer(struct spi_transfer *xfer,
 	spin_lock_irq(&mas->lock);
 	spin_unlock_irq(&mas->lock);
 
-	spi_tx_cfg = readl(se->base + SE_SPI_TRANS_CFG);
 	if (xfer->bits_per_word != mas->cur_bits_per_word) {
 		spi_setup_word_len(mas, mode, xfer->bits_per_word);
 		mas->cur_bits_per_word = xfer->bits_per_word;
@@ -364,8 +369,6 @@ static void setup_fifo_xfer(struct spi_transfer *xfer,
 	mas->tx_rem_bytes = 0;
 	mas->rx_rem_bytes = 0;
 
-	spi_tx_cfg &= ~CS_TOGGLE;
-
 	if (!(mas->cur_bits_per_word % MIN_WORD_LEN))
 		len = xfer->len * BITS_PER_BYTE / mas->cur_bits_per_word;
 	else
@@ -384,7 +387,6 @@ static void setup_fifo_xfer(struct spi_transfer *xfer,
 		writel(len, se->base + SE_SPI_RX_TRANS_LEN);
 		mas->rx_rem_bytes = xfer->len;
 	}
-	writel(spi_tx_cfg, se->base + SE_SPI_TRANS_CFG);
 
 	/*
 	 * Lock around right before we start the transfer since our
-- 
2.28.0.618.gf4bc123cb7-goog