Re: [PATCH 2/5] clocksource: Add Allwinner SoCs HS timers driver

From: Emilio López
Date: Sun Sep 29 2013 - 00:34:48 EST

Hi Maxime,

El 26/09/13 10:13, Maxime Ripard escribió:
On Wed, Sep 25, 2013 at 08:23:14PM -0300, Emilio López wrote:
El 25/09/13 11:03, Maxime Ripard escribió:
Most of the Allwinner SoCs (at this time, all but the A10) also have a
High Speed timers that are not using the 24MHz oscillator as a source
but rather the AHB clock running much faster.

The IP is slightly different between the A10s/A13 and the one used in
the A20/A31, since the latter have 4 timers available, while the former
have only 2 of them.

Signed-off-by: Maxime Ripard <maxime.ripard@xxxxxxxxxxxxxxxxxx>


+static void __init sun5i_timer_init(struct device_node *node)
+ unsigned long rate;
+ struct clk *clk;
+ int ret, irq;
+ u32 val;
+ timer_base = of_iomap(node, 0);
+ if (!timer_base)
+ panic("Can't map registers");
+ irq = irq_of_parse_and_map(node, 0);
+ if (irq <= 0)
+ panic("Can't parse IRQ");
+ clk = of_clk_get(node, 0);
+ if (IS_ERR(clk))
+ panic("Can't get timer clock");

I'm not familiar with clocksources, but does this have to be as
fatal as it is considering the kernel also supports the slower sun4i

Hmmm, I don't know, one might choose to enable only this timer, in that
case that would make sense to panic, since it would be the only timer in
that case.

Fair enough.

Also, would any special considerations be needed when adjusting the
ahb clock? A future cpufreq driver will most likely need to.

While this will be needed at some point, I don't really see how to
handle that properly. The clock framework doesn't seem to have any
callback when it comes to reconfiguring a clock that a device might

Maybe we should consider using one of the other timers; from a quick look at the A20 user manual, it seems they can run at ~200MHz ("PLL6/6" as input)

This will also creates trouble for IPs such as the I2C that have to
setup internal dividers, and use clk_get_rate to do so.

Not really, because they use APB1 which is not scaled. The manual makes it explicit when describing APB1:

"This clock is used for some special module apbclk(twi,uart,
ps2, can, scr). Because these modules need special clock rate
even if the apbclk changed."


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