[RFC] ath79: MikroTik RB912UAG-2HPnD: add initial value to SSR

[Denis Kalashnikov]

From: Denis Kalashnikov <denis281089 at gmail.com>

ar71xx mach-rb91x.c and others set SSR init value through
platform data (this ability is added to upstream
drivers/gpio/gpio-74x164.c by
451-gpio-74x164-improve-platform-device-support.patch).
When we ported RB912UAG-2HPnD to ath79, we used DTS gpio-exports
instead. But this broke some mPCIe cards. To fix this we
turn back to gpio-74x164 the ability to get an init value
from DTS.

Why is using DTS gpio-hog option not good in this case? Since
then gpio-export of the hogged line is not working. But we need
it, since with pcie_power and usb_power we can reset USB devices,
e.g cell modems.

Also move SSR beeper pin value from gpio-exports to SSR init value,
since user should never change its value.

Why did some mPCIe cards not work?
RouterBoot leaves USB port power and mPCIe port power lines on the
Serial Shift Register =1. In ar71xx firmware doesn't touch them -
ssr has the same intial values in march init code. In ath79 we
have a DTS instead, where gpio-export is used. When SSR has no
explicit default value, it uses 0 and there is a short period
when mPCIe and USP power lines are =0 (till gpio-export reasserts
them). And MikroTik mPCIe Wi-Fi 5Hz card R11e-5HacT doesn't work:
PCI driver when starts logs warning: "PCIe link is down", lspci
shows no device, rescan (echo 1 > /sys/bus/pci/rescan) doesn't work.

PCI controller (arch/mips/pci-ar724x) starts... and says: "PCIe link
is down", remembers this in the internal link_up field and never
re-check AR724x_PCI_RESET_LINK_UP register bit. When link_up is false,
pci read/write handlers always return error. When I patched it to
actually check link status before reading, I had kernel panic with
Device bus error when trying to read Vendor ID from config register
(see "MIPS: pci-ar724x: avoid data bus error due to a missing PCIe
module" Gabor Juhos patch). It seems that we need to somehow reinit
the PCI host controller. Or init it after gpio-exports. Or simply
don't touch mPCIe power. We prefer the last option.

Acknowledgments: Koen Vandeputte <koen.vandeputte at citymesh.com>
Reported-by: Thomas Hühn <thomas.huehn at hs-nordhausen.de>
Signed-off: Denis Kalashnikov <denis281089 at gmail.com>
---
 ...9342_mikrotik_routerboard-912uag-2hpnd.dts | 14 ++++++-------
 .../451-gpio-74x164-init-val-support.patch    | 20 +++++++++++++++++++
 2 files changed, 27 insertions(+), 7 deletions(-)
 create mode 100644 target/linux/ath79/patches-5.10/451-gpio-74x164-init-val-support.patch

diff --git a/target/linux/ath79/dts/ar9342_mikrotik_routerboard-912uag-2hpnd.dts b/target/linux/ath79/dts/ar9342_mikrotik_routerboard-912uag-2hpnd.dts
index 77a0d29113..b8dbe8b784 100644
--- a/target/linux/ath79/dts/ar9342_mikrotik_routerboard-912uag-2hpnd.dts
+++ b/target/linux/ath79/dts/ar9342_mikrotik_routerboard-912uag-2hpnd.dts
@@ -107,12 +107,6 @@
 	gpio-export {
 		compatible = "gpio-export";
 
-		beeper {
-			gpio-export,name = "beeper";
-			gpio-export,output = <1>;	/* Must be 1 to avoid EMI induced clicking noise */
-			gpios = <&ssr 5 GPIO_ACTIVE_HIGH>;
-		};
-
 		usb_power {
 			gpio-export,name = "power-usb";
 			gpio-export,output = <1>;
@@ -121,7 +115,7 @@
 
 		pcie_power {
 			gpio-export,name = "power-pcie";
-			gpio-export,output = <0>;
+			gpio-export,output = <1>;
 			gpios = <&ssr 7 GPIO_ACTIVE_HIGH>;
 		};
 	};
@@ -175,6 +169,12 @@
 		registers-number = <1>;
 		reg = <1>;
 		spi-max-frequency = <50000000>;
+
+		/*
+		bit 7 -- pcie_power, bit 6 -- usb_power, bit 5 -- beeper
+		power (must be 1 to avoid EMI induced clicking noise)
+		*/
+		init-data = /bits/ 8 <0xe0>;
 	};
 };
 
diff --git a/target/linux/ath79/patches-5.10/451-gpio-74x164-init-val-support.patch b/target/linux/ath79/patches-5.10/451-gpio-74x164-init-val-support.patch
new file mode 100644
index 0000000000..9dabb181b5
--- /dev/null
+++ b/target/linux/ath79/patches-5.10/451-gpio-74x164-init-val-support.patch
@@ -0,0 +1,20 @@
+--- a/drivers/gpio/gpio-74x164.c
++++ b/drivers/gpio/gpio-74x164.c
+@@ -145,6 +145,17 @@ static int gen_74x164_probe(struct spi_d
+ 	chip->gpio_chip.parent = &spi->dev;
+ 	chip->gpio_chip.owner = THIS_MODULE;
+ 
++	/*
++	 * Read optional inital value of registers. First byte -- last register.
++	 * E.g. init-data = /bits/ 8 <0x01 0x1f 0x02>;
++	 */
++	ret = of_property_read_u8_array(spi->dev.of_node, "init-data",
++		(u8 *)chip->buffer, (size_t)nregs);
++	if (ret && ret != -EINVAL /* Not found */) {
++		dev_err(&spi->dev, "Invalid 'init-data' property.\n");
++		return -EINVAL;
++	}
++
+ 	mutex_init(&chip->lock);
+ 
+ 	ret = __gen_74x164_write_config(chip);
-- 
2.31.1