rockchip/rk3288: Fix SPI clock divisor calculation

The code to calculate the RK3288 SPI controller's internal clock divisor
is wrong: it assumes that the divisor register was an "n-1" divisor when
it actually isn't (due to some misleading kernel code that was copied in
here). This means that all SPI clocks are currently running lower than
expected.

This patch fixes the calculation and changes all callers such that the
effective speeds stay the same.

BRANCH=veyron
BUG=chrome-os-partner:38352
TEST=Booted Jerry with and without the patch, dumping the divisor for
flash and EC clocks. Made sure it stays the same.

Change-Id: I2336e2b81c2384b5076175fcf32717a3ab2ba0c5
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 1fd5b990f937019a9bee7bd693c91d6e2fca1adb
Original-Change-Id: I094d57a5933c8b849f5c66194e6cc2952ab68b90
Original-Signed-off-by: Julius Werner <jwerner@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/262269
Original-Reviewed-by: David Hendricks <dhendrix@chromium.org>
Reviewed-on: http://review.coreboot.org/9887
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

1 files changed, 2 insertions, 6 deletions

diff --git a/src/soc/rockchip/rk3288/spi.c b/src/soc/rockchip/rk3288/spi.c
index aa70f3e0e5..a8d2be30fc 100644
--- a/src/soc/rockchip/rk3288/spi.c
+++ b/src/soc/rockchip/rk3288/spi.c
@@ -94,12 +94,8 @@ static void rockchip_spi_enable_chip(struct rockchip_spi *regs, int enable)
 
 static void rockchip_spi_set_clk(struct rockchip_spi *regs, unsigned int hz)
 {
-	unsigned short clk_div = 0;
-
-	/* Calculate clock divisor.  */
-	clk_div = SPI_SRCCLK_HZ / hz;
-	clk_div = (clk_div + 1) & 0xfffe;
-	assert((clk_div - 1) * hz == SPI_SRCCLK_HZ);
+	unsigned short clk_div = SPI_SRCCLK_HZ / hz;
+	assert(clk_div * hz == SPI_SRCCLK_HZ && !(clk_div & 1));
 	write32(&regs->baudr, clk_div);
 }