Am Montag, den 26.05.2014, 16:36 +0530 schrieb Viresh Kumar:

On 26 May 2014 16:15, Lucas Stach [off-list ref] wrote:

quoted

This driver handles the i.MX5 specific clock reparenting to be able to
reprogramm the PLL. cpufreq-cpu0 can only change a postdivider of the
PLL, which means we can't reach the exact OPP frequencies and can not
profit from the additional power savings of a slower running PLL.

Also without reprogramming the PLL we could possibly not scale to the
highest OPPs if the bootloader left the PLL at a slower rate. This is
the case for many i.MX53 boards, as the CPU regulator normally does
start up with the voltage required for 800MHz operation. If the
bootloader decides to not touch the regulator and set the PLL to 800MHz
the 1GHz and 1.2GHz operating points won't be useable.

Almost all users of cpufreq-cpu0 has such situations and they have
written a clock-driver for "cpu clock" to get this fixed. And they handle
all this PLL stuff in clk_set_rate() for this new clock..

I still couldn't find anything so special here that can't be fixed this way.
There is no point adding and maintaining a cpufreq driver if we can
use cpufreq-cpu0.

Ok I can push down the clock handling into the imx5 clk driver.

This leaves two more differences between imx5-cpufreq and cpufreq-cpu0:

1. Disabling of OPPs that could not be supported by the connected
regulator. I think this part can easily be made generic and pushed into
cpu0, as it should be beneficial to other SoCs too.

2. Usage of a fixed max voltage, rather than a voltage-tolerance. i.MX5
has a fixed maximum voltage, which is valid across all operating points.
I'm really opposed to using a tolerance value, where we instead could
have a well defined range. So for merging imx5-cpufreq into cpufreq-cpu0
this driver really need to handle this case.
Does adding a separate property for this, while keeping the
voltage-tolerance for the existing users, sound like a change you would
accept?

Regards,
Lucas

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