linux-kernel - [PATCH] spi/rockchip: Avoid accidentally turning off the clock

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Date:	Thu, 28 Aug 2014 16:43:48 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Mark Brown <broonie@...nel.org>, Addy Ke <addy.ke@...k-chips.com>,
	Heiko Stuebner <heiko@...ech.de>
Cc:	"Jeffy.Chen" <jeffy.chen@...k-chips.com>,
	Sonny Rao <sonnyrao@...omium.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	amstan@...omium.org, Doug Anderson <dianders@...omium.org>,
	linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, linux-spi@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH] spi/rockchip: Avoid accidentally turning off the clock

If our client is requesting a clock that is above the maximum clock
then the following division will result in 0:
  rs->max_freq / rs->speed

We'll then program 0 into the SPI_BAUDR register.  The Rockchip TRM
says: "If the value is 0, the serial output clock (sclk_out) is
disabled."

It's much better to end up with the fastest possible clock rather than
a clock that is off, so enforce a minimum value.

Signed-off-by: Doug Anderson <dianders@...omium.org>
---
 drivers/spi/spi-rockchip.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi-rockchip.c b/drivers/spi/spi-rockchip.c
index 6321326..cd0e08b0 100644
--- a/drivers/spi/spi-rockchip.c
+++ b/drivers/spi/spi-rockchip.c
@@ -499,7 +499,7 @@ static void rockchip_spi_config(struct rockchip_spi *rs)
 	}
 
 	/* div doesn't support odd number */
-	div = rs->max_freq / rs->speed;
+	div = max_t(u32, rs->max_freq / rs->speed, 1);
 	div = (div + 1) & 0xfffe;
 
 	spi_enable_chip(rs, 0);
-- 
2.1.0.rc2.206.gedb03e5

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