[PATCH 3/4] i2c: added I2C_AQ_NO_CLK_STRETCH to i2c-bcm2835.c
From: Eric Anholt <hidden>
Date: 2015-10-28 19:16:51
Also in:
linux-i2c, linux-iio
Nicola Corna [off-list ref] writes:
quoted hunk ↗ jump to hunk
As reported here http://www.advamation.com/knowhow/raspberrypi/rpi-i2c-bug.html the BCM2835 has a bug in its i2c implementation which prevents a correct clock stretching. Signed-off-by: Nicola Corna <redacted> --- drivers/i2c/busses/i2c-bcm2835.c | 5 +++++ 1 file changed, 5 insertions(+)diff --git a/drivers/i2c/busses/i2c-bcm2835.c b/drivers/i2c/busses/i2c-bcm2835.c index 3032b89..38d7102 100644 --- a/drivers/i2c/busses/i2c-bcm2835.c +++ b/drivers/i2c/busses/i2c-bcm2835.c@@ -222,6 +222,10 @@ static const struct i2c_algorithm bcm2835_i2c_algo = { .functionality = bcm2835_i2c_func, }; +static const struct i2c_adapter_quirks bcm2835_i2c_quirks = { + .flags = I2C_AQ_NO_CLK_STRETCH, +}; + static int bcm2835_i2c_probe(struct platform_device *pdev) { struct bcm2835_i2c_dev *i2c_dev;@@ -293,6 +297,7 @@ static int bcm2835_i2c_probe(struct platform_device *pdev) adap->algo = &bcm2835_i2c_algo; adap->dev.parent = &pdev->dev; adap->dev.of_node = pdev->dev.of_node; + adap->quirks = &bcm2835_i2c_quirks; bcm2835_i2c_writel(i2c_dev, BCM2835_I2C_C, 0);
Looking at the driver, we're not setting the REDL/FEDL fields, which are involved in the delays following clock stretching. Looks like I2C_DEL's low 16 bits (rising edge delay) should be I2C_DIV / 4 (wait half the period for the slave to update its data before we sample it), and the high 16 bits (falling edge delay) should be I2C_DIV / 16 (put our data out before we expet the slave to sample the value). Note: this is not a detailed analysis, nor am I asserting that this is the bug, just something that we seem to be missing in the Linux driver. (Added cc to linux-rpi-kernel, in case anyone on that list is interested in I2C issues on the platform) -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 818 bytes Desc: not available URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20151028/675f82b2/attachment.sig>