spi_qsd: Auto-select nearest lower available clock rate
Specifying max clock frequency for SPI, via platform data, requires
a frequency that is available to SPI. The frequencies that are
available to SPI and the devices max-frequency are specified in
different places and in different files. As a result theses values
can easily go out of sync.
SPI devices typically can operate at some maximum frequency, with
some tolerance for the actual-frequency being lower. SPI users
typically know their target-device's max-speed, but they have
to dig in platform data files to find the best matching frequency
that is available.
This patch lets users specify the device's max-frequency, while the
actual frequency is automatically selected by the driver. The selected
frequency is the same as the requested one, or the nearest lower one.
CRs-Fixed: 467687
Change-Id: I293ec1b66ad56e4a2b4643482917f79dabd7a758
Signed-off-by: Gilad Avidov <gavidov@codeaurora.org>
Signed-off-by: Alok Chauhan <alokc@codeaurora.org>
diff --git a/drivers/spi/spi_qsd.c b/drivers/spi/spi_qsd.c
index 5ba244f..4f2b2d2 100644
--- a/drivers/spi/spi_qsd.c
+++ b/drivers/spi/spi_qsd.c
@@ -126,13 +126,72 @@
}
}
+/**
+ * msm_spi_clk_max_rate: finds the nearest lower rate for a clk
+ * @clk the clock for which to find nearest lower rate
+ * @rate clock frequency in Hz
+ * @return nearest lower rate or negative error value
+ *
+ * Public clock API extends clk_round_rate which is a ceiling function. This
+ * function is a floor function implemented as a binary search using the
+ * ceiling function.
+ */
+static long msm_spi_clk_max_rate(struct clk *clk, unsigned long rate)
+{
+ long lowest_available, nearest_low, step_size, cur;
+ long step_direction = -1;
+ long guess = rate;
+ int max_steps = 10;
+
+ cur = clk_round_rate(clk, rate);
+ if (cur == rate)
+ return rate;
+
+ /* if we got here then: cur > rate */
+ lowest_available = clk_round_rate(clk, 0);
+ if (lowest_available > rate)
+ return -EINVAL;
+
+ step_size = (rate - lowest_available) >> 1;
+ nearest_low = lowest_available;
+
+ while (max_steps-- && step_size) {
+ guess += step_size * step_direction;
+
+ cur = clk_round_rate(clk, guess);
+
+ if ((cur < rate) && (cur > nearest_low))
+ nearest_low = cur;
+
+ /*
+ * if we stepped too far, then start stepping in the other
+ * direction with half the step size
+ */
+ if (((cur > rate) && (step_direction > 0))
+ || ((cur < rate) && (step_direction < 0))) {
+ step_direction = -step_direction;
+ step_size >>= 1;
+ }
+ }
+ return nearest_low;
+}
+
static void msm_spi_clock_set(struct msm_spi *dd, int speed)
{
+ long rate;
int rc;
- rc = clk_set_rate(dd->clk, speed);
+ rate = msm_spi_clk_max_rate(dd->clk, speed);
+ if (rate < 0) {
+ dev_err(dd->dev,
+ "%s: no match found for requested clock frequency:%d",
+ __func__, speed);
+ return;
+ }
+
+ rc = clk_set_rate(dd->clk, rate);
if (!rc)
- dd->clock_speed = speed;
+ dd->clock_speed = rate;
}
static int msm_spi_calculate_size(int *fifo_size,