On some platforms, the clocks might be registered by a platform
driver. When this is the case, the clock platform driver may very well
be probed after xhci-plat, in which case the first probe() invocation
of xhci-plat will receive -EPROBE_DEFER as the return value of
devm_clk_get().
The current code handles that as a normal error, and simply assumes
that this means that the system doesn't have a clock for the XHCI
controller, and continues probing without calling
clk_prepare_enable(). Unfortunately, this doesn't work on systems
where the XHCI controller does have a clock, but that clock is
provided by another platform driver. In order to fix this situation,
we handle the -EPROBE_DEFER error condition specially, and abort the
XHCI controller probe(). It will be retried later automatically, the
clock will be available, devm_clk_get() will succeed, and the probe()
will continue with the clock prepared and enabled as expected.
In practice, such issue is seen on the ARM64 Marvell 7K/8K platform,
where the clocks are registered by a platform driver.
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@xxxxxxxxxxxxxxxxxx>
---
Changes since v1:
- Re-order how the EPROBE_DEFER error handling is done, according to
a suggestion from Heikki Krogerus
<heikki.krogerus@xxxxxxxxxxxxxxx>.
---
drivers/usb/host/xhci-plat.c | 3 +++
1 file changed, 3 insertions(+)
diff --git a/drivers/usb/host/xhci-plat.c b/drivers/usb/host/xhci-plat.c
index 5c15e9b..bc6dfbc 100644
--- a/drivers/usb/host/xhci-plat.c
+++ b/drivers/usb/host/xhci-plat.c
@@ -181,6 +181,9 @@ static int xhci_plat_probe(struct platform_device *pdev)
ret = clk_prepare_enable(clk);
if (ret)
goto put_hcd;
+ } else if (PTR_ERR(clk) == -EPROBE_DEFER) {
+ ret = -EPROBE_DEFER;
+ goto put_hcd;
}
xhci = hcd_to_xhci(hcd);
--
2.6.4
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