[U-Boot] [PATCH 09/20] tegra: spi: Support slow SPI rates

Simon Glass
2015-02-17T22:29:43Z

Use the oscillator as the source clock when we cannot achieve a low-enough
speed with the peripheral clock. This happens when we request 3MHz on a SPI
clock, for example.

Signed-off-by: Simon Glass <sjg@chromium.org>
---

drivers/spi/tegra114_spi.c | 18 +++++++++++++++---
1 file changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/tegra114_spi.c b/drivers/spi/tegra114_spi.c
index a73c6b0..1c5368b 100644
--- a/drivers/spi/tegra114_spi.c
+++ b/drivers/spi/tegra114_spi.c
@@ -143,6 +143,7 @@ static int tegra114_spi_probe(struct udevice *bus)
{
struct tegra_spi_platdata *plat = dev_get_platdata(bus);
struct tegra114_spi_priv *priv = dev_get_priv(bus);
+ ulong rate;

priv->regs = (struct spi_regs *)plat->base;

@@ -150,9 +151,20 @@ static int tegra114_spi_probe(struct udevice *bus)
priv->freq = plat->frequency;
priv->periph_id = plat->periph_id;

- /* Change SPI clock to correct frequency, PLLP_OUT0 source */
- clock_start_periph_pll(priv->periph_id, CLOCK_ID_PERIPH,
- priv->freq);
+ /*
+ * Change SPI clock to correct frequency, PLLP_OUT0 source, falling
+ * back to the oscillator if that is too fast.
+ */
+ rate = clock_start_periph_pll(priv->periph_id, CLOCK_ID_PERIPH,
+ priv->freq);
+ if (rate > priv->freq + 100000) {
+ rate = clock_start_periph_pll(priv->periph_id, CLOCK_ID_OSC,
+ priv->freq);
+ if (rate != priv->freq) {
+ printf("Warning: SPI '%s' requested clock %u, actual clock %lu\n",
+ bus->name, priv->freq, rate);
+ }
+ }

setbits_le32(&priv->regs->command1, SPI_CMD1_M_S | SPI_CMD1_CS_SW_HW |
(priv->mode << SPI_CMD1_MODE_SHIFT) | SPI_CMD1_CS_SW_VAL);
--
2.2.0.rc0.207.ga3a616c