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Diffstat (limited to 'Documentation/getting_started/gpio.md')
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diff --git a/Documentation/getting_started/gpio.md b/Documentation/getting_started/gpio.md index 5d5623a5d9..829c41a0fc 100644 --- a/Documentation/getting_started/gpio.md +++ b/Documentation/getting_started/gpio.md @@ -162,6 +162,80 @@ The first is configuring a pin as an output, when it was designed to be an input. There is a real risk in this case of short-circuiting a component which could cause catastrophic failures, up to and including your mainboard! +### Intel SoCs + +As per Intel Platform Controller Hub (PCH) EDS since Skylake, a GPIO PAD register +supports four different types of GPIO reset as: + ++------------------------+----------------+-------------+-------------+ +| | | PAD Reset ? | ++ PAD Reset Config + Platform Reset +-------------+-------------+ +| | | GPP | GPD | ++------------------------+----------------+-------------+-------------+ +| 00 - Power Good | Warm Reset | N | N | +| (GPP: RSMRST, +----------------+-------------+-------------+ +| GPD: DSW_PWROK) | Cold Reset | N | N | +| +----------------+-------------+-------------+ +| | S3/S4/S5 | N | N | +| +----------------+-------------+-------------+ +| | Global Reset | N | N | +| +----------------+-------------+-------------+ +| | Deep Sx | Y | N | +| +----------------+-------------+-------------+ +| | G3 | Y | Y | ++------------------------+----------------+-------------+-------------+ +| 01 - Deep | Warm Reset | Y | Y | +| +----------------+-------------+-------------+ +| | Cold Reset | Y | Y | +| +----------------+-------------+-------------+ +| | S3/S4/S5 | N | N | +| +----------------+-------------+-------------+ +| | Global Reset | Y | Y | +| +----------------+-------------+-------------+ +| | Deep Sx | Y | Y | +| +----------------+-------------+-------------+ +| | G3 | Y | Y | ++------------------------+----------------+-------------+-------------+ +| 10 - Host Reset/PLTRST | Warm Reset | Y | Y | +| +----------------+-------------+-------------+ +| | Cold Reset | Y | Y | +| +----------------+-------------+-------------+ +| | S3/S4/S5 | Y | Y | +| +----------------+-------------+-------------+ +| | Global Reset | Y | Y | +| +----------------+-------------+-------------+ +| | Deep Sx | Y | Y | +| +----------------+-------------+-------------+ +| | G3 | Y | Y | ++------------------------+----------------+-------------+-------------+ +| 11 - Resume Reset | Warm Reset | - | N | +| (GPP: Reserved, +----------------+-------------+-------------+ +| GPD: RSMRST) | Cold Reset | - | N | +| +----------------+-------------+-------------+ +| | S3/S4/S5 | - | N | +| +----------------+-------------+-------------+ +| | Global Reset | - | N | +| +----------------+-------------+-------------+ +| | Deep Sx | - | Y | +| +----------------+-------------+-------------+ +| | G3 | - | Y | ++------------------------+----------------+-------------+-------------+ + +Each GPIO Community has a Pad Configuration Lock register for a GPP allowing locking +specific register fields in the PAD configuration register. + +The Pad Config Lock registers reset type is default hardcoded to **Power Good** and +it's **not** configurable by GPIO PAD DW0.PadRstCfg. Hence, it may appear that for a GPP, +the Pad Reset Config (DW0 Bit 31) is configured differently from `Power Good`. + +This would create confusion where the Pad configuration is returned to its `default` +value but remains `locked`, this would prevent software to reprogram the GPP. +Additionally, this means software can't rely on GPIOs being reset by PLTRST# or Sx entry. + +Hence, as per GPIO BIOS Writers Guide (BWG) it's recommended to change the Pad Reset +Configuration for lock GPP as `Power Good` so that pad configuration and lock bit are +always in sync and can be reset at the same time. + ## Soft Straps Soft straps, that can be configured by the vendor in the Intel Flash Image Tool |