6.1-stable review patch. If anyone has any objections, please let me know.
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From: Mike Looijmans mike.looijmans@topic.nl
commit 38d6e60b6f3a99f8f13bee22eab616136c2c0675 upstream.
The "reset" GPIO controls the RESET signal to an external, usually ULPI PHY, chip. The original code path acquires the signal in LOW state, and then immediately asserts it HIGH again, if the reset signal defaulted to asserted, there'd be a short "spike" before the reset.
Here is what happens depending on the pre-existing state of the reset signal: Reset (previously asserted): ~~~|_|~~~~|_______ Reset (previously deasserted): _____|~~~~|_______ ^ ^ ^ A B C
At point A, the low going transition is because the reset line is requested using GPIOD_OUT_LOW. If the line is successfully requested, the first thing we do is set it high _without_ any delay. This is point B. So, a glitch occurs between A and B.
Requesting the line using GPIOD_OUT_HIGH eliminates the A and B transitions. Instead we get:
Reset (previously asserted) : ~~~~~~~~~~|______ Reset (previously deasserted): ____|~~~~~|______ ^ ^ A C
Where A and C are the points described above in the code. Point B has been eliminated.
The issue was found during code inspection.
Also remove the cryptic "toggle ulpi .." comment.
Fixes: ca05b38252d7 ("usb: dwc3: xilinx: Add gpio-reset support") Cc: stable stable@kernel.org Signed-off-by: Mike Looijmans mike.looijmans@topic.nl Reviewed-by: Radhey Shyam Pandey radhey.shyam.pandey@amd.com Acked-by: Thinh Nguyen Thinh.Nguyen@synopsys.com Link: https://lore.kernel.org/r/20250318064518.9320-1-mike.looijmans@topic.nl Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/usb/dwc3/dwc3-xilinx.c | 4 +--- 1 file changed, 1 insertion(+), 3 deletions(-)
--- a/drivers/usb/dwc3/dwc3-xilinx.c +++ b/drivers/usb/dwc3/dwc3-xilinx.c @@ -208,15 +208,13 @@ static int dwc3_xlnx_init_zynqmp(struct
skip_usb3_phy: /* ulpi reset via gpio-modepin or gpio-framework driver */ - reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_LOW); + reset_gpio = devm_gpiod_get_optional(dev, "reset", GPIOD_OUT_HIGH); if (IS_ERR(reset_gpio)) { return dev_err_probe(dev, PTR_ERR(reset_gpio), "Failed to request reset GPIO\n"); }
if (reset_gpio) { - /* Toggle ulpi to reset the phy. */ - gpiod_set_value_cansleep(reset_gpio, 1); usleep_range(5000, 10000); gpiod_set_value_cansleep(reset_gpio, 0); usleep_range(5000, 10000);