diff options
Diffstat (limited to 'drivers/i2c')
| -rw-r--r-- | drivers/i2c/busses/i2c-s3c2410.c | 47 |
1 files changed, 45 insertions, 2 deletions
diff --git a/drivers/i2c/busses/i2c-s3c2410.c b/drivers/i2c/busses/i2c-s3c2410.c index 86e60f598c51..a44e2130d3e0 100644 --- a/drivers/i2c/busses/i2c-s3c2410.c +++ b/drivers/i2c/busses/i2c-s3c2410.c @@ -235,8 +235,47 @@ static inline void s3c24xx_i2c_stop(struct s3c24xx_i2c *i2c, int ret) dev_dbg(i2c->dev, "STOP\n"); - /* stop the transfer */ - iicstat &= ~S3C2410_IICSTAT_START; + /* + * The datasheet says that the STOP sequence should be: + * 1) I2CSTAT.5 = 0 - Clear BUSY (or 'generate STOP') + * 2) I2CCON.4 = 0 - Clear IRQPEND + * 3) Wait until the stop condition takes effect. + * 4*) I2CSTAT.4 = 0 - Clear TXRXEN + * + * Where, step "4*" is only for buses with the "HDMIPHY" quirk. + * + * However, after much experimentation, it appears that: + * a) normal buses automatically clear BUSY and transition from + * Master->Slave when they complete generating a STOP condition. + * Therefore, step (3) can be done in doxfer() by polling I2CCON.4 + * after starting the STOP generation here. + * b) HDMIPHY bus does neither, so there is no way to do step 3. + * There is no indication when this bus has finished generating + * STOP. + * + * In fact, we have found that as soon as the IRQPEND bit is cleared in + * step 2, the HDMIPHY bus generates the STOP condition, and then + * immediately starts transferring another data byte, even though the + * bus is supposedly stopped. This is presumably because the bus is + * still in "Master" mode, and its BUSY bit is still set. + * + * To avoid these extra post-STOP transactions on HDMI phy devices, we + * just disable Serial Output on the bus (I2CSTAT.4 = 0) directly, + * instead of first generating a proper STOP condition. This should + * float SDA & SCK terminating the transfer. Subsequent transfers + * start with a proper START condition, and proceed normally. + * + * The HDMIPHY bus is an internal bus that always has exactly two + * devices, the host as Master and the HDMIPHY device as the slave. + * Skipping the STOP condition has been tested on this bus and works. + */ + if (i2c->quirks & QUIRK_HDMIPHY) { + /* Stop driving the I2C pins */ + iicstat &= ~S3C2410_IICSTAT_TXRXEN; + } else { + /* stop the transfer */ + iicstat &= ~S3C2410_IICSTAT_START; + } writel(iicstat, i2c->regs + S3C2410_IICSTAT); i2c->state = STATE_STOP; @@ -561,6 +600,10 @@ static int s3c24xx_i2c_doxfer(struct s3c24xx_i2c *i2c, else if (ret != num) dev_dbg(i2c->dev, "incomplete xfer (%d)\n", ret); + /* For QUIRK_HDMIPHY, bus is already disabled */ + if (i2c->quirks & QUIRK_HDMIPHY) + goto out; + /* ensure the stop has been through the bus */ dev_dbg(i2c->dev, "waiting for bus idle\n"); |