diff --git a/Documentation/RFC/intel-gpio-cleanup.md b/Documentation/RFC/intel-gpio-cleanup.md new file mode 100644 index 000000000000..130132b56f3c --- /dev/null +++ b/Documentation/RFC/intel-gpio-cleanup.md @@ -0,0 +1,98 @@ +# Background + +CB:31250 ("soc/intel/cannonlake: Configure GPIOs again after FSP-S is +done") introduced a workaround in coreboot for `soc/intel/cannonlake` +platforms to save and restore GPIO configuration performed by +mainboard across call to FSP Silicon Init (FSP-S). This workaround was +required because FSP-S was configuring GPIOs differently than +mainboard resulting in boot and runtime issues because of +misconfigured GPIOs. This issue was observed on `google/hatch` +mainboard and was raised with Intel to get the FSP behavior +fixed. Until the fix in FSP was available, this workaround was used to +ensure that the mainboards can operate correctly and were not impacted +by the GPIO misconfiguration in FSP-S. + +The issues observed on `google/hatch` mainboard were fixed by adding +(if required) and initializing appropriate FSP UPDs. This UPD +initialization ensured that FSP did not configure any GPIOs +differently than the mainboard configuration. Fixes included: + * CB:31375 ("soc/intel/cannonlake: Configure serial debug uart") + * CB:31520 ("soc/intel/cannonlake: Assign FSP UPDs for HPD and Data/CLK of DDI ports") + * CB:32176 ("mb/google/hatch: Update GPIO settings for SD card and SPI1 Chip select") + * CB:34900 ("soc/intel/cnl: Add provision to configure SD controller write protect pin") + +With the above changes merged, it was verified on `google/hatch` +mainboard that the workaround for GPIO reconfiguration was not +needed. However, at the time, we missed dropping the workaround in +'soc/intel/cannonlake`. Currently, this workaround is used by the +following mainboards: + * `google/drallion` + * `google/sarien` + * `purism/librem_cnl` + * `system76/lemp9` + +As verified on `google/hatch`, FSP v1263 included all UPD additions +that were required for addressing this issue. + +# Proposal + +* The workaround can be safely dropped from `soc/intel/cannonlake` + only after the above mainboards have verified that FSP-S does not + configure any pads differently than the mainboard in coreboot. Since + the fix included initialization of FSP UPDs correctly, the above + mainboards can use the following diff to check what pads change + after FSP-S has run: + +``` +diff --git a/src/soc/intel/common/block/gpio/gpio.c b/src/soc/intel/common/block/gpio/gpio.c +index 28e78fb366..0cce41b316 100644 +--- a/src/soc/intel/common/block/gpio/gpio.c ++++ b/src/soc/intel/common/block/gpio/gpio.c +@@ -303,10 +303,10 @@ static void gpio_configure_pad(const struct pad_config *cfg) + /* Patch GPIO settings for SoC specifically */ + soc_pad_conf = soc_gpio_pad_config_fixup(cfg, i, soc_pad_conf); + +- if (CONFIG(DEBUG_GPIO)) ++ if (soc_pad_conf != pad_conf) + printk(BIOS_DEBUG, +- "gpio_padcfg [0x%02x, %02zd] DW%d [0x%08x : 0x%08x" +- " : 0x%08x]\n", ++ "%d: gpio_padcfg [0x%02x, %02zd] DW%d [0x%08x : 0x%08x" ++ " : 0x%08x]\n", cfg->pad, + comm->port, relative_pad_in_comm(comm, cfg->pad), i, + pad_conf,/* old value */ + cfg->pad_config[i],/* value passed from gpio table */ +``` + +Depending upon the pads that are misconfigured by FSP-S, these +mainboards will have to set UPDs appropriately. Once this is verified +by the above mainboards, the workaround implemented in CB:31250 can be +dropped. + +* The fix implemented in FSP/coreboot for `soc/intel/cannonlake` + platforms is not really the right long term solution for the + problem. Ideally, FSP should not be touching any GPIO configuration + and letting coreboot configure the pads as per mainboard + design. This recommendation was accepted and implemented by Intel + starting with Jasper Lake and Tiger Lake platforms using a single + UPD `GpioOverride` that coreboot can set so that FSP does not change + any GPIO configuration. However, this implementation is not + backported to any older platforms. Given the issues that we have + observed across different platforms, the second proposal is to: + + - Add a Kconfig `CHECK_GPIO_CONFIG_CHANGES` that enables checks + in coreboot to stash GPIO pad configuration before various calls + to FSP and compares the configuration on return from FSP. + - This will have to be implemented as part of + drivers/intel/fsp/fsp2_0/ to check for the above config selection + and make callbacks `gpio_snapshot()` and `gpio_verify_snapshot()` + to identify and print information about pads that have changed + configuration after calls to FSP. + - This config can be kept disabled by default and mainboard + developers can enable them as and when required for debug. + - This will be helpful not just for the `soc/intel/cannonlake` + platforms that want to get rid of the above workaround, but also + for all future platforms using FSP to identify and catch any GPIO + misconfigurations that might slip in to any platforms (in case the + `GpioOverride` UPD is not honored by any code path within FSP). +