Soft straps, that can be configured by the vendor in the Intel Flash
Image Tool (FIT), can influence some pads' default state. It is possible
to select either a native function or GPIO mode for some pads on
non-server SoCs, while on server SoCs most pads can be controlled.
Thus, add a recommendation to always configure all pads for a board to
guarantee integrity between different board or vendor firmware revisions
where the soft straps might have been changed.
Change-Id: I33063a3f6a1c9cd5267d85f7da84deb554489a26
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52297
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Intel PDGs starting from Skylake / Sunrise Point state that, different
from the general recommendation in digital electronics, unconnected
GPIOs defaulting to GPIO mode do explicitly not require termination.
The reason for this is, that these GPIOs have the `GPIORXDIS` bit set,
which effectively disconnects the pad from the internal logic by
disabling the input buffer.
This bit - besides `GPIOTXDIS` - can also be set explicitly by using
the gpio macro `PAD_NC(pad, NONE)`.
In some cases, a pull resistor may be required due to bad board design
or when a vendor sets the RX/TX disable bits together with a pull
resistor and schematics are not available to check if the pad is really
unconnected or just unused. In this case the pull resistor should be
kept.
Pads defaulting to native functions usually don't need special handling.
However, when pads requiring external pull-ups are missing these due to
bad board design, they should be configured with `PAD_NC` to disconnect
them internally.
Rewrite the documentation to reflect these new findings.
Also clarify the comment in soc/intel gpio code accordingly.
Change-Id: Id01b197ebe8f2b8bb4ecf3d119ec2298b26d9be0
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52139
Reviewed-by: Tim Crawford <tcrawford@system76.com>
Reviewed-by: Felix Singer <felixsinger@posteo.net>
Reviewed-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Drop LPC pad configuration code since all boards now do pad
configuration on their own. The comment about LPC_CLKRUNB when using
eSPI is moved to `Documentation/getting_started/gpio.md`.
Change-Id: I710d6aee8c3b2c8282cd321cd0688b9b26abea07
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/49410
Reviewed-by: Angel Pons <th3fanbus@gmail.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
This macro is not correct because the RX Level/Edge Configuration
(trig) and the GPIO Tx/Rx Buffer Disable (bufdis) fields in DW0
register do not affect on the pad in the native function mode.
This is part of the patch set
"src/mb/*, src/soc/intel/common/gpio: Remove PAD_CFG_NF_BUF_TRIG ":
CB:43455 - cedarisland: undo set trig and bufdis for NF pads
CB:43454 - tiogapass: undo set trig and bufdis for NF pads
CB:43561 - h110m: undo set trig and bufdis for NF pads
CB:43569 - soc/intel/common/gpio_defs: Remove PAD_CFG_NF_BUF_TRIG
Change-Id: Ic0416e3f67016c648f0886df73f585e8a08d4e92
Signed-off-by: Maxim Polyakov <max.senia.poliak@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/43569
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Lance Zhao
Reviewed-by: Michael Niewöhner
The new documentation describes typical ways that mainboards will
set up their GPIOs, as well as the distinction between "early"
and "normal" GPIOs. It also describes the typical properties
that GPIO configuration will cover.
Change-Id: I279eec4ed2bb0248a2bdb363fb73b40b8272267f
Signed-off-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/37802
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Justin TerAvest <teravest@chromium.org>
Michael Niewöhner