Re: [PATCH v3 7/8] net: phy: Add support to configure clock in Broadcom iProc mdio mux

From: Russell King - ARM Linux
Date: Wed Aug 01 2018 - 16:23:42 EST

On Wed, Aug 01, 2018 at 10:07:12PM +0200, Andrew Lunn wrote:
> You might want to consider adding clk_optional_get() and
> devm_clk_optional_get().

I think there's attempts to add such APIs but I don't think it's
trivial - it seems to require a _lot_ of discussion.

I think part of that is because of the quirky use of error codes.
If you look at clk_get(), it calls __of_clk_get_by_name() which

-ENOENT if DT is disabled
-ENOENT if the device has no DT node
-EPROBE_DEFER if the lookup in DT succeeds but there's no registered
-EINVAL if the device has a DT node but the lookup of the name
failed (in otherwords, the optional clock was omitted)
-ENOENT if the clocks = property has not enough clocks for the
clock-names property
-ENOMEM if we fail to allocate the clk
-ENOENT if __clk_get() fails

or any other error code returned via of_clk_provider's ->get() method.

The use of -EINVAL, one of the most common error codes, makes it
difficult to be sure that the clock is not specified in DT.

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