linux-kernel - Re: [PATCH 1/2] clk: mvebu: set flags in CP110 gate clock

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Date:   Tue, 30 Aug 2016 15:10:10 +0200
From:   Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:     Marcin Wojtas <mw@...ihalf.com>
Cc:     linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-clk@...r.kernel.org, sboyd@...eaurora.org,
        mturquette@...libre.com, andrew@...n.ch, jason@...edaemon.net,
        tn@...ihalf.com, nadavh@...vell.com, alior@...vell.com,
        jaz@...ihalf.com, gregory.clement@...e-electrons.com,
        sebastian.hesselbarth@...il.com
Subject: Re: [PATCH 1/2] clk: mvebu: set flags in CP110 gate clock

Hello,

On Tue, 23 Aug 2016 08:26:48 +0200, Marcin Wojtas wrote:

> diff --git a/drivers/clk/mvebu/cp110-system-controller.c b/drivers/clk/mvebu/cp110-system-controller.c
> index 7fa42d6..0835e1d 100644
> --- a/drivers/clk/mvebu/cp110-system-controller.c
> +++ b/drivers/clk/mvebu/cp110-system-controller.c
> @@ -144,6 +144,7 @@ static struct clk *cp110_register_gate(const char *name,
>  
>  	init.name = name;
>  	init.ops = &cp110_gate_ops;
> +	init.flags = CLK_IS_BASIC;

Is this really correct?

The documentation for CLK_IS_BASIC is pretty slim, but it says:

   #define CLK_IS_BASIC            BIT(5) /* Basic clk, can't do a to_clk_foo() */

However, we *do* have a to_clk_*() macro in this driver:

struct cp110_gate_clk {
        struct clk_hw hw;
        struct regmap *regmap;
        u8 bit_idx;
};

#define to_cp110_gate_clk(clk) container_of(clk, struct cp110_gate_clk, hw)

If you read the commit log of commit
f7d8caadfd2813cbada82ce9041b13c38e8e5282, which introduced the flag, it
says:

    clk: Add CLK_IS_BASIC flag to identify basic clocks
    
    Most platforms end up using a mix of basic clock types and
    some which use clk_hw_foo struct for filling in custom platform
    information when the clocks don't fit into basic types supported.
    
    In platform code, its useful to know if a clock is using a basic
    type or clk_hw_foo, which helps platforms know if they can
    safely use to_clk_hw_foo to derive the clk_hw_foo pointer from
    clk_hw.
    
    Mark all basic clocks with a CLK_IS_BASIC flag.
    
    Signed-off-by: Rajendra Nayak <rnayak@...com>
    Signed-off-by: Mike Turquette <mturquette@...aro.org>

We are in the case where we have our own clk_hw_foo structure, and a
to_clk_hw_foo macro to derive the clk_hw_foo from clk_hw.

According to this, the CP110 clocks are *not* basic clocks, and
therefore we shouldn't have this flag. Perhaps just the memset() is
missing.

Thanks,

Thomas
-- 
Thomas Petazzoni, CTO, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com