Patch "usb: xhci-plat: properly handle probe deferral for devm_clk_get()" has been added to the 4.6-stable tree

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 the 4.6-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
usb-xhci-plat-properly-handle-probe-deferral-for-devm_clk_get.patch
and it can be found in the queue-4.6 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

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()

From: Thomas Petazzoni <[email protected]>

commit de95c40d5beaa47f6dc8fe9ac4159b4672b51523 upstream.

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(+)

@@ -194,6 +194,9 @@ static int xhci_plat_probe(struct platfo
 		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);

Patches currently in stable-queue which might be from [email protected] are

queue-4.6/usb-xhci-plat-properly-handle-probe-deferral-for-devm_clk_get.patch