linux-kernel - [PATCH 2/4] spi: a3700: Set frequency limits at startup

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Date:   Wed, 17 Jan 2018 17:15:26 +0100
From:   Maxime Chevallier <maxime.chevallier@...le.fr>
To:     broonie@...nel.org
Cc:     linux-spi@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        gregory.clement@...e-electrons.com,
        Maxime Chevallier <maxime.chevallier@...le.fr>
Subject: [PATCH 2/4] spi: a3700: Set frequency limits at startup

Armada 3700 SPI controller has an internal clock divider which can
divide the parent clock frequency by up to 30.

This patch sets the limits in the spi_controller fields so that we can
detect when a non-supported frequency is requested by a device for a
transfer.

Signed-off-by: Maxime Chevallier <maxime.chevallier@...le.fr>
---
 drivers/spi/spi-armada-3700.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/spi/spi-armada-3700.c b/drivers/spi/spi-armada-3700.c
index c11ea6c..8048468 100644
--- a/drivers/spi/spi-armada-3700.c
+++ b/drivers/spi/spi-armada-3700.c
@@ -27,6 +27,8 @@
 
 #define DRIVER_NAME			"armada_3700_spi"
 
+#define A3700_SPI_MAX_SPEED_HZ		100000000
+#define A3700_SPI_MAX_PRESCALE		30
 #define A3700_SPI_TIMEOUT		10
 
 /* SPI Register Offest */
@@ -823,6 +825,11 @@ static int a3700_spi_probe(struct platform_device *pdev)
 		goto error;
 	}
 
+	master->max_speed_hz = min_t(unsigned long, A3700_SPI_MAX_SPEED_HZ,
+					clk_get_rate(spi->clk));
+	master->min_speed_hz = DIV_ROUND_UP(clk_get_rate(spi->clk),
+						A3700_SPI_MAX_PRESCALE);
+
 	ret = a3700_spi_init(spi);
 	if (ret)
 		goto error_clk;
-- 
2.1.4