diff options
Diffstat (limited to 'drivers/i2c/busses/i2c-mxs.c')
| -rw-r--r-- | drivers/i2c/busses/i2c-mxs.c | 94 |
1 files changed, 55 insertions, 39 deletions
diff --git a/drivers/i2c/busses/i2c-mxs.c b/drivers/i2c/busses/i2c-mxs.c index e55736077d23..22d8ad353409 100644 --- a/drivers/i2c/busses/i2c-mxs.c +++ b/drivers/i2c/busses/i2c-mxs.c @@ -93,35 +93,6 @@ #define MXS_CMD_I2C_READ (MXS_I2C_CTRL0_SEND_NAK_ON_LAST | \ MXS_I2C_CTRL0_MASTER_MODE) -struct mxs_i2c_speed_config { - uint32_t timing0; - uint32_t timing1; - uint32_t timing2; -}; - -/* - * Timing values for the default 24MHz clock supplied into the i2c block. - * - * The bus can operate at 95kHz or at 400kHz with the following timing - * register configurations. The 100kHz mode isn't present because it's - * values are not stated in the i.MX233/i.MX28 datasheet. The 95kHz mode - * shall be close enough replacement. Therefore when the bus is configured - * for 100kHz operation, 95kHz timing settings are actually loaded. - * - * For details, see i.MX233 [25.4.2 - 25.4.4] and i.MX28 [27.5.2 - 27.5.4]. - */ -static const struct mxs_i2c_speed_config mxs_i2c_95kHz_config = { - .timing0 = 0x00780030, - .timing1 = 0x00800030, - .timing2 = 0x00300030, -}; - -static const struct mxs_i2c_speed_config mxs_i2c_400kHz_config = { - .timing0 = 0x000f0007, - .timing1 = 0x001f000f, - .timing2 = 0x00300030, -}; - /** * struct mxs_i2c_dev - per device, private MXS-I2C data * @@ -137,7 +108,9 @@ struct mxs_i2c_dev { struct completion cmd_complete; int cmd_err; struct i2c_adapter adapter; - const struct mxs_i2c_speed_config *speed; + + uint32_t timing0; + uint32_t timing1; /* DMA support components */ int dma_channel; @@ -153,9 +126,16 @@ static void mxs_i2c_reset(struct mxs_i2c_dev *i2c) { stmp_reset_block(i2c->regs); - writel(i2c->speed->timing0, i2c->regs + MXS_I2C_TIMING0); - writel(i2c->speed->timing1, i2c->regs + MXS_I2C_TIMING1); - writel(i2c->speed->timing2, i2c->regs + MXS_I2C_TIMING2); + /* + * Configure timing for the I2C block. The I2C TIMING2 register has to + * be programmed with this particular magic number. The rest is derived + * from the XTAL speed and requested I2C speed. + * + * For details, see i.MX233 [25.4.2 - 25.4.4] and i.MX28 [27.5.2 - 27.5.4]. + */ + writel(i2c->timing0, i2c->regs + MXS_I2C_TIMING0); + writel(i2c->timing1, i2c->regs + MXS_I2C_TIMING1); + writel(0x00300030, i2c->regs + MXS_I2C_TIMING2); writel(MXS_I2C_IRQ_MASK << 8, i2c->regs + MXS_I2C_CTRL1_SET); } @@ -553,6 +533,43 @@ static bool mxs_i2c_dma_filter(struct dma_chan *chan, void *param) return true; } +static void mxs_i2c_derive_timing(struct mxs_i2c_dev *i2c, int speed) +{ + /* The I2C block clock run at 24MHz */ + const uint32_t clk = 24000000; + uint32_t base; + uint16_t high_count, low_count, rcv_count, xmit_count; + struct device *dev = i2c->dev; + + if (speed > 540000) { + dev_warn(dev, "Speed too high (%d Hz), using 540 kHz\n", speed); + speed = 540000; + } else if (speed < 12000) { + dev_warn(dev, "Speed too low (%d Hz), using 12 kHz\n", speed); + speed = 12000; + } + + /* + * The timing derivation algorithm. There is no documentation for this + * algorithm available, it was derived by using the scope and fiddling + * with constants until the result observed on the scope was good enough + * for 20kHz, 50kHz, 100kHz, 200kHz, 300kHz and 400kHz. It should be + * possible to assume the algorithm works for other frequencies as well. + * + * Note it was necessary to cap the frequency on both ends as it's not + * possible to configure completely arbitrary frequency for the I2C bus + * clock. + */ + base = ((clk / speed) - 38) / 2; + high_count = base + 3; + low_count = base - 3; + rcv_count = (high_count * 3) / 4; + xmit_count = low_count / 4; + + i2c->timing0 = (high_count << 16) | rcv_count; + i2c->timing1 = (low_count << 16) | xmit_count; +} + static int mxs_i2c_get_ofdata(struct mxs_i2c_dev *i2c) { uint32_t speed; @@ -572,12 +589,12 @@ static int mxs_i2c_get_ofdata(struct mxs_i2c_dev *i2c) } ret = of_property_read_u32(node, "clock-frequency", &speed); - if (ret) + if (ret) { dev_warn(dev, "No I2C speed selected, using 100kHz\n"); - else if (speed == 400000) - i2c->speed = &mxs_i2c_400kHz_config; - else if (speed != 100000) - dev_warn(dev, "Unsupported I2C speed selected, using 100kHz\n"); + speed = 100000; + } + + mxs_i2c_derive_timing(i2c, speed); return 0; } @@ -621,7 +638,6 @@ static int mxs_i2c_probe(struct platform_device *pdev) return err; i2c->dev = dev; - i2c->speed = &mxs_i2c_95kHz_config; init_completion(&i2c->cmd_complete); |