phy: marvell: phy-mvebu-a3700-comphy: Reset COMPHY registers before USB 3.0 power on

Turris MOX board with older ARM Trusted Firmware version v1.5 is not able
to detect any USB 3.0 device connected to USB-A port on Mox-A module after
commit 0a6fc70d ("phy: marvell: phy-mvebu-a3700-comphy: Remove broken
reset support"). On the other hand USB 2.0 devices connected to the same
USB-A port are working fine.

It looks as if the older firmware configures COMPHY registers for USB 3.0
somehow incompatibly for kernel driver. Experiments show that resetting
COMPHY registers via setting SFT_RST auto-clearing bit in COMPHY_SFT_RESET
register fixes this issue.

Reset the COMPHY in mvebu_a3700_comphy_usb3_power_on() function as a first
step after selecting COMPHY lane and USB 3.0 function. With this change
Turris MOX board can successfully detect USB 3.0 devices again.

Before the above mentioned commit this reset was implemented in PHY reset
method, so this is the reason why there was no issue with older firmware
version then.

Fixes: 0a6fc70d ("phy: marvell: phy-mvebu-a3700-comphy: Remove broken reset support")
Reported-by: Marek Behún <kabel@kernel.org>
Signed-off-by: Pali Rohár <pali@kernel.org>
Tested-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Link: https://lore.kernel.org/r/20220920121154.30115-1-pali@kernel.orgSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/phy/marvell/phy-mvebu-a3700-comphy.c

@@ -826,6 +826,9 @@ mvebu_a3700_comphy_usb3_power_on(struct mvebu_a3700_comphy_lane *lane)
 	if (ret)
 		return ret;
 
+	/* COMPHY register reset (cleared automatically) */
+	comphy_lane_reg_set(lane, COMPHY_SFT_RESET, SFT_RST, SFT_RST);
+
 	/*
 	 * 0. Set PHY OTG Control(0x5d034), bit 4, Power up OTG module The
 	 * register belong to UTMI module, so it is set in UTMI phy driver.