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

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Date:   Wed, 1 Aug 2018 21:23:14 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Arun Parameswaran <arun.parameswaran@...adcom.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>, netdev@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH v3 7/8] net: phy: Add support to configure clock in
 Broadcom iProc mdio mux

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
returns:

 -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
   clock
 -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.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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