[PATCH v2 4/7] clk: Add simple gated clock

[Turquette, Mike]

On Mon, Sep 26, 2011 at 12:37 PM, Jamie Iles <jamie at jamieiles.com> wrote:
> On Mon, Sep 26, 2011 at 02:10:32PM -0500, Rob Herring wrote:
>> On 09/26/2011 01:40 PM, Jamie Iles wrote:
>> > On Mon, Sep 26, 2011 at 01:33:08PM -0500, Rob Herring wrote:
>> >>> +static void clk_gate_set_bit(struct clk_hw *clk)
>> >>> +{
>> >>> + struct clk_gate *gate = to_clk_gate(clk);
>> >>> + u32 reg;
>> >>> +
>> >>> + reg = __raw_readl(gate->reg);
>> >>> + reg |= BIT(gate->bit_idx);
>> >>> + __raw_writel(reg, gate->reg);
>> >>
>> >> Don't these read-mod-writes need a spinlock around it?
>> >>
>> >> It's possible to have an enable bits and dividers in the same register.
>> >> If you did a set_rate and while doing an enable/disable, there would be
>> >> a problem. Also, it may be 2 different clocks in the same register, so
>> >> the spinlock needs to be shared and not per clock.
>> >
>> > Well the prepare lock will be held here and I believe that would be
>> > sufficient.
>>
>> No, the enable spinlock is protecting enable/disable. But set_rate is
>> protected by the prepare mutex. So you clearly don't need locking if you
>> have a register of only 1 bit enables. If you have a register accessed
>> by both enable/disable and prepare/unprepare/set_rate, then you need
>> some protection.
>
> OK fair point, but I would guess that if you had a clock like this then
> you probably wouldn't use this simple gated clock would you?  (speaking
> from my world where we have quite simple clocks ;-))

I think it is a safe assumption that if a register controls both
enable/disable and some programmable divider then,

1) those controls are probably for the same clock
2) that clock won't be using the cookie-cutter gated-clock
implementation anyways

Rob, do you feel these assumptions are OK and locking can remain the
same in this patch?

Regards,
Mike

> Jamie
>