Re: [PATCH 1/6] clk: sunxi: Add support for sun9i a80 usb clocks and resets

Maxime Ripard
2014-11-05T09:45:24Z

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Hi Russell,

On Tue, Nov 04, 2014 at 06:12:19PM +0000, Russell King - ARM Linux wrote:
> On Tue, Nov 04, 2014 at 12:07:14PM +0800, Chen-Yu Tsai wrote:
> > + spin_lock_irqsave(data->lock, flags);
> > +
> > + reg = readl(data->reg);
> > + writel(reg & ~BIT(id), data->reg);
> > +
> > + spin_unlock_irqrestore(data->lock, flags);
>
> Don't we have generic support for atomic modification of register
> values? Hmm, we have it for ARM only - atomic_io_modify() and
> atomic_io_modify_relaxed().
>
> I guess we should push for those to become cross-arch if we end up
> with generic drivers shared between other architectures.

IIRC, the atomic MMIO accessors are doing exactly that, but with a
global lock for all MMIO accesses, while here we protect a single
register.

I'm not really sure that sharing this spinlock across the whole system
is worth it and scales that well.

Maxime

--
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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