[coreboot-gerrit] Change in coreboot[master]: mb/google/poppy/variant/atlas: I2C: run trackpad at 1MHz

[Caveh Jalali (Code Review)]

Hello Gaggery Tsai, caveh jalali, Duncan Laurie, Gaggery Tsai, build bot (Jenkins), Furquan Shaikh, 

I'd like you to reexamine a change. Please visit

    https://review.coreboot.org/29553

to look at the new patch set (#3).

Change subject: mb/google/poppy/variant/atlas: I2C: run trackpad at 1MHz
......................................................................

mb/google/poppy/variant/atlas: I2C: run trackpad at 1MHz

With this change, coreboot thinks we're running at 1MHz:
	DW I2C bus 2 at 0xd1133000 (1000 KHz)

Elan eKT3644 IC Specification (trackpad) requires:
Low Time  larger than 500ns (61 * 8.3ns = 506ns).
High Time larger than 260ns (32 * 8.3ns = 265ns),
Data Hold_time larger than 0ns.
Start Condition Hold time larger than 250ns.
Rise/Fall time of less than 120ns.

HCNT controls both High Time and Start Condition Hold time.
LCNT controls Low Time.
SDA_HOLD controls Data Hold Time.

P2 Atlas "Rise time" is 90ns and "Fall time" is 32ns and tuned
using resistors on the board and must be considered when
adjusting any of the parameters since these times are all measured
at 30 or 70% of base and peak voltages (0v/1.8v).

The eKT3644 requirements are met with LCNT=69, HCNT=33, SDA_HOLD=20
which yields the SCL at around 950KHz - suboptimal but compliant.

Lower LCNT or HCNT results in "lost arbitration" errors or not complying
with eKT3644 requirements.

Verified by gaggery.tsai at intel.corp-partner.google.com.
Scope shots posted here:
https://b.corp.google.com/issues/78601949#comment177

BUG=b:78601949
BRANCH=none
TEST=Farzam provided test points on track pad for SCL/SDA/GND.
     Waveforms measured with oscilloscope and screen shots attached
     to bug (comment #177, #155, #100).
     Operate trackpad/touchscreen
     Review dmesg (kernel) output for correct speed, parameters, and
     no errors (e.g. "lost arbitration" or "host controller timeout")

Change-Id: Iaf42ba7b8818b7cd9c8dcc657823dac705659d38
Signed-off-by: Caveh Jalali <caveh at chromium.org>
Signed-off-by: Grant Grundler <grundler at chromium.org>
Tested-by: gaggery.tsai at intel.corp-partner.google.com
Tested-by: grundler at chromium.org
---
M src/mainboard/google/poppy/variants/atlas/devicetree.cb
1 file changed, 8 insertions(+), 6 deletions(-)


  git pull ssh://review.coreboot.org:29418/coreboot refs/changes/53/29553/3
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Gerrit-Project: coreboot
Gerrit-Branch: master
Gerrit-MessageType: newpatchset
Gerrit-Change-Id: Iaf42ba7b8818b7cd9c8dcc657823dac705659d38
Gerrit-Change-Number: 29553
Gerrit-PatchSet: 3
Gerrit-Owner: Caveh Jalali <caveh at google.com>
Gerrit-Reviewer: Caveh Jalali <caveh at google.com>
Gerrit-Reviewer: Duncan Laurie <dlaurie at chromium.org>
Gerrit-Reviewer: Furquan Shaikh <furquan at google.com>
Gerrit-Reviewer: Gaggery Tsai <gaggery.tsai at intel.com>
Gerrit-Reviewer: Gaggery Tsai <gaggery.tsai at intel.corp-partner.google.com>
Gerrit-Reviewer: build bot (Jenkins) <no-reply at coreboot.org>
Gerrit-Reviewer: caveh jalali <caveh at chromium.org>
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