From 20edd1ac7ae7d081078dd64ffe7a89f48c09fd65 Mon Sep 17 00:00:00 2001 From: Simon Glass Date: Fri, 5 Jun 2015 14:39:35 -0600 Subject: tegra: spi: Support slow SPI rates 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 Signed-off-by: Tom Warren --- 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 0d69376e4e0..d7eecd5bc60 100644 --- a/drivers/spi/tegra114_spi.c +++ b/drivers/spi/tegra114_spi.c @@ -144,6 +144,7 @@ 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); struct spi_regs *regs; + ulong rate; priv->regs = (struct spi_regs *)plat->base; regs = priv->regs; @@ -152,9 +153,20 @@ 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); + } + } /* Clear stale status here */ setbits_le32(®s->fifo_status, -- cgit v1.2.3