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authorHeiko Stuebner <heiko@sntech.de>2016-02-22 14:55:01 +0300
committerKishon Vijay Abraham I <kishon@ti.com>2016-03-01 14:43:50 +0300
commit605df8af33a7b206611a7bda01384b2b46d80e17 (patch)
tree33987d6c34543b6e573df11e98c3f0f69ace5392 /Documentation/kernel-parameters.txt
parent12df9c50568a08db0b38fb70f088b80ec2793191 (diff)
downloadlinux-605df8af33a7b206611a7bda01384b2b46d80e17.tar.xz
phy: rockchip-usb: add handler for usb-uart functionality
Most newer Rockchip SoCs provide the possibility to use a usb-phy as passthrough for the debug uart (uart2), making it possible to for example get console output without needing to open the device. This patch adds an early_initcall to enable this functionality conditionally via the commandline and also disables the corresponding usb controller in the devicetree. Currently only data for the rk3288 is provided, but at least the rk3188 and arm64 rk3368 also provide this functionality and will be enabled later. On a spliced usb cable the signals are tx on white wire(D+) and rx on green wire(D-). The one caveat is that currently the reconfiguration of the phy happens as early_initcall, as the code depends on the unflattened devicetree being available. Everything is fine if only a regular console is active as the console-replay will happen after the reconfiguation. But with earlycon active output up to smp-init currently will get lost. The phy is an optional property for the connected dwc2 controller, so we still provide the phy device but fail all phy-ops with -EBUSY to make sure the dwc2 does not try to transmit anything on the repurposed phy. Signed-off-by: Heiko Stuebner <heiko@sntech.de> Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Diffstat (limited to 'Documentation/kernel-parameters.txt')
-rw-r--r--Documentation/kernel-parameters.txt6
1 files changed, 6 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 87d40a72f6a1..d91417b6c88e 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -3486,6 +3486,12 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
ro [KNL] Mount root device read-only on boot
+ rockchip.usb_uart
+ Enable the uart passthrough on the designated usb port
+ on Rockchip SoCs. When active, the signals of the
+ debug-uart get routed to the D+ and D- pins of the usb
+ port and the regular usb controller gets disabled.
+
root= [KNL] Root filesystem
See name_to_dev_t comment in init/do_mounts.c.