linux-obmc: Work around host IPL issues using GPIO hogs in Palmetto devicetree

The commit message in the kernel patch applied by this commit outlines
the critical information on how it was generated and the limitations
that apply to using GPIO hogs to produce a bootable host.

Please refer to the kernel patch commit message.

Note the patch is best applied during the OpenBMC build process, rather
than being carried by the OpenBMC kernel fork. The OpenBMC kernel fork is
used to test Aspeed SoC support at large, often with non-OpenBMC
userspaces. While the OpenBMC userspace is sometimes not used in kernel
testing, the tests often take place on OpenBMC supported machines such as
the Palmetto. As kernel development and maintenance often includes
exporting various GPIOs to poke at, it's best that we minimise the
number of GPIOs tied up in hogs.

It's acknowledged that this opens an opportunity for predictable flaws
if a kernel is booted with the OpenBMC userspace without this patch
applied, but it's assumed the user knows what they are doing in this
case*.

* Having said that, it will no doubt trip me up.

Change-Id: I08f5f5b29cc81257655bb9a35dbb6c5ce3f11292
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>

2 files changed, 252 insertions, 0 deletions

diff --git a/meta-openbmc-bsp/meta-aspeed/meta-ast2400/recipes-kernel/linux/linux-obmc/0001-work-around-aspeed-bmc-opp-palmetto-Add-GPIO-hogs-to.patch b/meta-openbmc-bsp/meta-aspeed/meta-ast2400/recipes-kernel/linux/linux-obmc/0001-work-around-aspeed-bmc-opp-palmetto-Add-GPIO-hogs-to.patch
new file mode 100644
index 000000000..038797b19
--- /dev/null
+++ b/meta-openbmc-bsp/meta-aspeed/meta-ast2400/recipes-kernel/linux/linux-obmc/0001-work-around-aspeed-bmc-opp-palmetto-Add-GPIO-hogs-to.patch
@@ -0,0 +1,251 @@
+From 5362492a7546230866dc4a45269bb3dae65306cb Mon Sep 17 00:00:00 2001
+From: Andrew Jeffery <andrew@aj.id.au>
+Date: Fri, 2 Sep 2016 12:22:41 +0930
+Subject: [PATCH] work-around: aspeed-bmc-opp-palmetto: Add GPIO hogs to
+ devicetree
+
+This is a work-in-progress patch that attempts to emulate the GPIO
+state originally written by the mach-aspeed board file.
+
+It isn't entirely analogous: Whilst values might be set in the GPIO
+data/direction registers, this doesn't mean the GPIO IP was in control
+of the pins affected by the bits in question. However, the content of
+the patch is derived directly from the data and direction values that
+Steve Faure reported[1] from a Palmetto running the OpenBMC stable branch.
+
+Secondly, the patch pays no regard to the prescribed active state of the lines
+and assumes active high for all pins. This is not a reflection of the
+description in the schematic, and neither do the configured GPIO values
+necessarily reflect the prescribed initial values from the schematic.
+
+A starting point for the patch was generated from the following Python script:
+
+	 #!/usr/bin/python3
+	 import sys
+
+	 from collections import namedtuple
+
+	 GpioRegsetConfig = namedtuple("GpioRegsetConfig", "banks value direction")
+	 banks = ( "ABCD", "EFGH" )
+
+	 broken = (
+		 GpioRegsetConfig(banks[0], 0x130F8CE3, 0x01706074),
+		 GpioRegsetConfig(banks[1], 0x9F48F7FF, 0x00004002)
+	 )
+
+	 working = (
+		 GpioRegsetConfig(banks[0], 0x130F8CE3, 0x0370E677),
+		 GpioRegsetConfig(banks[1], 0x0370E677, 0xC738F202)
+	 )
+
+	 GpioConfig = namedtuple("GpioConfig", "bank index direction state active")
+
+	 def gpio_dt(name, config):
+	     fmt = "pin_gpio_{} {{\n\tgpio-hog;\n\tgpios = <ASPEED_GPIO({}, {}) {}>;\n\t{};\n\tline-name = \"{}\";\n}};"
+	     if "output" == config.direction:
+		 state = "{}-{}".format(config.direction, config.state)
+	     else:
+		 state = config.direction
+	     return fmt.format(
+		 name.lower(),
+		 config.bank,
+		 config.index,
+		 "GPIO_ACTIVE_HIGH",
+		 state,
+		 name)
+
+	 def tell_gpios(config, change):
+	     for i, bank in enumerate(config.banks):
+		 for j in range(0, 8):
+		     bi = i * 8 + j;
+		     if ((1 << bi) & change) > 0:
+			 gpio = "{}{}".format(bank, j)
+			 if (bi & config.direction) > 0:
+			     sd = "output"
+			     value = "high" if (bi & config.value) > 0 else "low"
+			 else:
+			     sd = "input"
+			     value = None
+			 dtconfig = GpioConfig(bank, j, sd, value, "GPIO_ACTIVE_HIGH")
+			 print(gpio_dt(gpio, dtconfig))
+			 print()
+
+	 def main():
+	     for b, w in zip(broken, working):
+		 cd = b.direction ^ w.direction
+		 tell_gpios(w, cd)
+
+	 if __name__ == "__main__":
+	     main()
+
+The generated patch was tested on a Pass 2 Palmetto. It was found that with the
+patch and an OpenBMC userspace generated at v1.99.0-60-g2b717d8489c1, the host
+could:
+
+* Boot to Petitboot
+* Reboot to Petitboot
+* Survive a reboot of the BMC (remain functional at the Petitboot shell)
+* Be powered off by the BMC after reboot
+
+Reports from Andrew Geissler[2] and Cédric Le Goater[3] suggest mixed results
+across the Palmetto fleet, but this patch at least represents a step forwards.
+
+For the above reasons and those below, this patch is a temporary work-around:
+
+* GPIOs configured as hogs cannot have their line state changed once initialised
+* GPIOs configured as hogs will not be exposed to userspace even if requested
+
+These two issues combined deny capabilities such as Cronus. The ultimate
+solution is userspace daemon(s) requesting and controlling the GPIOs as
+desired.
+
+[1] https://github.com/openbmc/openbmc/issues/527#issuecomment-244239595
+[2] https://github.com/openbmc/openbmc/issues/513#issuecomment-244454018
+[3] https://github.com/openbmc/openbmc/issues/513#issuecomment-244414523
+
+Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
+---
+ arch/arm/boot/dts/aspeed-bmc-opp-palmetto.dts | 127 ++++++++++++++++++++++++++
+ 1 file changed, 127 insertions(+)
+
+diff --git a/arch/arm/boot/dts/aspeed-bmc-opp-palmetto.dts b/arch/arm/boot/dts/aspeed-bmc-opp-palmetto.dts
+index 21619fd8cd8d..5c689613e5bd 100644
+--- a/arch/arm/boot/dts/aspeed-bmc-opp-palmetto.dts
++++ b/arch/arm/boot/dts/aspeed-bmc-opp-palmetto.dts
+@@ -167,6 +167,133 @@
+ 		output-low;
+ 		line-name = "func_mode2";
+ 	};
++
++	pin_gpio_a0 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(A, 0) GPIO_ACTIVE_HIGH>;
++		input;
++		line-name = "A0";
++	};
++
++	pin_gpio_a1 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(A, 1) GPIO_ACTIVE_HIGH>;
++		output-high;
++		line-name = "A1";
++	};
++
++	pin_gpio_b1 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(B, 1) GPIO_ACTIVE_HIGH>;
++		output-high;
++		line-name = "B1";
++	};
++
++	pin_gpio_b2 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(B, 2) GPIO_ACTIVE_HIGH>;
++		output-high;
++		line-name = "B2";
++	};
++
++	pin_gpio_b7 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(B, 7) GPIO_ACTIVE_HIGH>;
++		output-high;
++		line-name = "B7";
++	};
++
++	pin_gpio_d1 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(D, 1) GPIO_ACTIVE_HIGH>;
++		output-high;
++		line-name = "D1";
++	};
++
++	pin_gpio_f1 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(F, 1) GPIO_ACTIVE_HIGH>;
++		input;
++		line-name = "F1";
++	};
++
++	pin_gpio_f4 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(F, 4) GPIO_ACTIVE_HIGH>;
++		input;
++		line-name = "F4";
++	};
++
++	pin_gpio_f5 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(F, 5) GPIO_ACTIVE_HIGH>;
++		input;
++		line-name = "F5";
++	};
++
++	pin_gpio_f7 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(F, 7) GPIO_ACTIVE_HIGH>;
++		output-high;
++		line-name = "F7";
++	};
++
++	pin_gpio_g3 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(G, 3) GPIO_ACTIVE_HIGH>;
++		output-high;
++		line-name = "G3";
++	};
++
++	pin_gpio_g4 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(G, 4) GPIO_ACTIVE_HIGH>;
++		input;
++		line-name = "G4";
++	};
++
++	pin_gpio_g5 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(G, 5) GPIO_ACTIVE_HIGH>;
++		input;
++		line-name = "G5";
++	};
++
++	pin_gpio_h0 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(H, 0) GPIO_ACTIVE_HIGH>;
++		input;
++		line-name = "H0";
++	};
++
++	pin_gpio_h1 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(H, 1) GPIO_ACTIVE_HIGH>;
++		input;
++		line-name = "H1";
++	};
++
++	pin_gpio_h2 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(H, 2) GPIO_ACTIVE_HIGH>;
++		output-high;
++		line-name = "H2";
++	};
++
++	pin_gpio_h6 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(H, 6) GPIO_ACTIVE_HIGH>;
++		output-high;
++		line-name = "H6";
++	};
++
++	pin_gpio_h7 {
++		gpio-hog;
++		gpios = <ASPEED_GPIO(H, 7) GPIO_ACTIVE_HIGH>;
++		output-high;
++		line-name = "H7";
++	};
++
+ };
+ 
+ &vuart {
+-- 
+2.7.4
+
diff --git a/meta-openbmc-bsp/meta-aspeed/meta-ast2400/recipes-kernel/linux/linux-obmc_%.bbappend b/meta-openbmc-bsp/meta-aspeed/meta-ast2400/recipes-kernel/linux/linux-obmc_%.bbappend
index 6d7ae271e..6034b891b 100644
--- a/meta-openbmc-bsp/meta-aspeed/meta-ast2400/recipes-kernel/linux/linux-obmc_%.bbappend
+++ b/meta-openbmc-bsp/meta-aspeed/meta-ast2400/recipes-kernel/linux/linux-obmc_%.bbappend
@@ -1,2 +1,3 @@
 FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"
 SRC_URI += "file://defconfig"
+SRC_URI += "file://0001-work-around-aspeed-bmc-opp-palmetto-Add-GPIO-hogs-to.patch"