linux-kernel - [PATCH] spi: spi-geni-qcom: Don't set the cs if it was already right

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Date:   Fri, 26 Jun 2020 15:19:50 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     linux-arm-msm@...r.kernel.org, swboyd@...omium.org,
        Dilip Kota <dkota@...eaurora.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Douglas Anderson <dianders@...omium.org>,
        linux-kernel@...r.kernel.org, linux-spi@...r.kernel.org
Subject: [PATCH] spi: spi-geni-qcom: Don't set the cs if it was already right

Setting the chip select on the Qualcomm geni SPI controller isn't
exactly cheap.  Let's cache the current setting and avoid setting the
chip select if it's already right.

Using "flashrom" to read or write the EC firmware on a Chromebook
shows roughly a 25% reduction in interrupts and a 15% speedup.

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

 drivers/spi/spi-geni-qcom.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-geni-qcom.c b/drivers/spi/spi-geni-qcom.c
index 5b1dca1fff79..e99a9d57449f 100644
--- a/drivers/spi/spi-geni-qcom.c
+++ b/drivers/spi/spi-geni-qcom.c
@@ -79,6 +79,7 @@ struct spi_geni_master {
 	unsigned int oversampling;
 	spinlock_t lock;
 	int irq;
+	bool cs_flag;
 };
 
 static int get_spi_clk_cfg(unsigned int speed_hz,
@@ -146,10 +147,15 @@ static void spi_geni_set_cs(struct spi_device *slv, bool set_flag)
 	struct geni_se *se = &mas->se;
 	unsigned long time_left;
 
-	pm_runtime_get_sync(mas->dev);
 	if (!(slv->mode & SPI_CS_HIGH))
 		set_flag = !set_flag;
 
+	if (set_flag == mas->cs_flag)
+		return;
+
+	mas->cs_flag = set_flag;
+
+	pm_runtime_get_sync(mas->dev);
 	spin_lock_irq(&mas->lock);
 	reinit_completion(&mas->cs_done);
 	if (set_flag)
-- 
2.27.0.212.ge8ba1cc988-goog