[PATCH v4 1/2] usb: ulpi: defer ulpi_register on ulpi_read_id timeout

[Ferry Toth <ftoth@exalondelft.nl>]

Since commit 0f0101719138 ("usb: dwc3: Don't switch OTG -> peripheral if extcon is present")
Dual Role support on Intel Merrifield platform broke due to rearranging
the call to dwc3_get_extcon().

It appears to be caused by ulpi_read_id() on the first test write failing
with -ETIMEDOUT. Currently ulpi_read_id() expects to discover the phy via
DT when the test write fails and returns 0 in that case, even if DT does not
provide the phy. As a result usb probe completes without phy.

On Intel Merrifield the issue is reproducible but difficult to find the
root cause. Using an ordinary kernel and rootfs with buildroot ulpi_read_id()
succeeds. As soon as adding ftrace / bootconfig to find out why,
ulpi_read_id() fails and we can't analyze the flow. Using another rootfs
ulpi_read_id() fails even without adding ftrace. Appearantly the issue is
some kind of timing / race, but merely retrying ulpi_read_id() does not
resolve the issue.

This patch makes ulpi_read_id() return -ETIMEDOUT to its user if the first
test write fails. The user should then handle it appropriately. A follow up
patch will make dwc3_core_init() set -EPROBE_DEFER in this case and bail out.

Fixes: ef6a7bcfb01c ("usb: ulpi: Support device discovery via DT")
Cc: stable@vger.kernel.org

Signed-off-by: Ferry Toth <ftoth@exalondelft.nl>
---
 drivers/usb/common/ulpi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/usb/common/ulpi.c b/drivers/usb/common/ulpi.c
index d7c8461976ce..60e8174686a1 100644
--- a/drivers/usb/common/ulpi.c
+++ b/drivers/usb/common/ulpi.c
@@ -207,7 +207,7 @@ static int ulpi_read_id(struct ulpi *ulpi)
 	/* Test the interface */
 	ret = ulpi_write(ulpi, ULPI_SCRATCH, 0xaa);
 	if (ret < 0)
-		goto err;
+		return ret;
 
 	ret = ulpi_read(ulpi, ULPI_SCRATCH);
 	if (ret < 0)
-- 
2.37.2