Re: [PATCH 3/4] i2c: qup: Correct duty cycle for FM and FM+

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hey Sricharan,

On 4/13/2018 12:14 AM, Sricharan R wrote:
Hi Austin,

On 4/5/2018 1:14 AM, Austin Christ wrote:
The I2C spec UM10204 Rev. 6 specifies the following timings.

            Standard      Fast Mode     Fast Mode Plus
SCL low    4.7us         1.3us         0.5us
SCL high   4.0us         0.6us         0.26us

This results in a 33%/66% duty cycle as opposed to the 50%/50% duty cycle
used for Standard-mode.

Add High Time Divider settings to correct duty cycle for FM(400kHz) and
FM+(1MHz).

Signed-off-by: Austin Christ <austinwc@xxxxxxxxxxxxxx>
---
  drivers/i2c/busses/i2c-qup.c | 10 ++++++++--
  1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/i2c/busses/i2c-qup.c b/drivers/i2c/busses/i2c-qup.c
index cb14687..2a88611 100644
--- a/drivers/i2c/busses/i2c-qup.c
+++ b/drivers/i2c/busses/i2c-qup.c
@@ -1858,9 +1858,15 @@ static int qup_i2c_probe(struct platform_device *pdev)
  	size = QUP_INPUT_FIFO_SIZE(io_mode);
  	qup->in_fifo_sz = qup->in_blk_sz * (2 << size);
- fs_div = ((src_clk_freq / clk_freq) / 2) - 3;
  	hs_div = 3;
-	qup->clk_ctl = (hs_div << 8) | (fs_div & 0xff);
+	if (clk_freq <= I2C_STANDARD_FREQ) {
+		fs_div = ((src_clk_freq / clk_freq) / 2) - 3;
+		qup->clk_ctl = (hs_div << 8) | (fs_div & 0xff);
+	} else {
+		/* 33%/66% duty cycle */
+		fs_div = ((src_clk_freq / clk_freq) - 6) * 2 / 3;
+		qup->clk_ctl = ((fs_div / 2) << 16) | (hs_div << 8) | (fs_div & 0xff);
+	}
  while here, can we add a small comment for the above calculation. why the -3 above and -6 ?

Good question. This is the exact math recommended in the HPG for fs_div with and without the high time divider set. There is not explanation for the differences in the math in the hardware documentation that I've seen. What is the preferred way for documenting something like this in comments?

Regards,
  Sricharan


--
Qualcomm Datacenter Technologies as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.
--
To unsubscribe from this list: send the line "unsubscribe linux-arm-msm" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html



[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [Linux for Sparc]     [IETF Annouce]     [Security]     [Bugtraq]     [Linux MIPS]     [ECOS]     [Asterisk Internet PBX]     [Linux API]

  Powered by Linux