patch "usb: xhci-plat: properly handle probe deferral for devm_clk_get()" added to usb-linus

This is a note to let you know that I've just added the patch titled

usb: xhci-plat: properly handle probe deferral for devm_clk_get()

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From: Thomas Petazzoni <[email protected]>
Date: Wed, 1 Jun 2016 18:09:09 +0300
Subject: usb: xhci-plat: properly handle probe deferral for devm_clk_get()

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.

---
 drivers/usb/host/xhci-plat.c | 3 +++
 1 file changed, 3 insertions(+)

index 676ea458148b..1f3f981fe7f8 100644
@@ -196,6 +196,9 @@ 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);

2.8.3