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    SubjectRe: [PATCH v3 2/3] ARM: imx: Add imx5 cpuidle driver
    On Thu, May 10, 2012 at 7:41 AM, Sascha Hauer <s.hauer@pengutronix.de> wrote:
    > On Wed, May 09, 2012 at 09:27:02AM -0500, Rob Lee wrote:
    >> Sascha,
    >>
    >> >
    >> > This clk_get should go away here and be moved somewhere to
    >> > initialization. Also, if getting this clock fails we can still
    >> > do regular cpu_do_idle. Additionally, if clk_get fails, we'll
    >> > have a ERR_PTR value in gpc_dvfs_clk in which case the
    >> > gpc_dvfs_clk == NULL won't trigger next time you are here and
    >> > then you'll enable a nonexisting clock below.
    >> >
    >>
    >> Agree.  I'd prefer to enable this clock during intialization and just
    >> leave it running.  It is supposed to be a very low power clock and I
    >> couldn't measuring any power difference with and without it being
    >> enabled
    >
    > Ok, even better.
    >
    >> >
    >> > I wonder why you don't add the default ARM_CPUIDLE_WFI_STATE_PWR state.
    >> > The above is something different, right? It has a greater exit latency
    >> > than ARM_CPUIDLE_WFI_STATE_PWR, so why don't we add it here aswell?
    >>
    >> Yes and no.  Yes this is a different state but no, it doesn't have a
    >> significantly greater exit latency, or at least a large enough exit
    >> latency to warrant an extra state in my opinion.  According to the
    >> i.MX5 documentation, the extra exit time beyond basic WFI required for
    >> the  "WAIT_UNCLOCKED_POWER_OFF" state is 500ns (this is due to a
    >> difference in i.MX5 hardware implementation compared to all other ARM
    >> platforms).  In reality, it did require a few more microseconds to
    >> perform in my testing just based on the extra register writes in
    >> mx5_cpu_lp_set().  I'd like to clean up mx5_cpu_lp_set() and add a
    >> global variable to track the previous state and to just exit out if
    >> the new state is the same as the old.
    >
    > Do you think it's worth it? You buy skipping the read with an additional
    > test.
    >

    I'll run some tests to check.

    Thanks,
    Rob

    >> I could do this cleanup as part of this patchset if you prefer that.
    >
    > Yes please. Cleanups before adding new features is always a good reason
    > to apply a patch series ;)
    >
    > Sascha
    >
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