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To:     Alex Elder <elder@linaro.org>,
        David Dai <daidavid1@codeaurora.org>,
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From:   Stephen Boyd <sboyd@kernel.org>
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Subject: Re: [RFC PATCH] clk: qcom: clk-rpmh: Add IPA clock support
Date:   Thu, 06 Dec 2018 10:02:20 -0800
Sender: linux-kernel-owner@vger.kernel.org
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Quoting David Dai (2018-12-05 17:24:18)
> =

> =

> On 12/4/2018 11:15 PM, Stephen Boyd wrote:
> > Quoting David Dai (2018-12-04 17:14:10)
> >> On 12/4/2018 2:34 PM, Stephen Boyd wrote:
> >>> Quoting Alex Elder (2018-12-04 13:41:47)
> >>>>
> >>> But then we translate that clock rate into a bandwidth request to the
> >>> BCM hardware? Seems really weird because it's doing the opposite of w=
hat
> >>> you say is abusive. What does the IPA driver plan to do with this clk?
> >>> Calculate a frequency by knowing that it really boils down to some
> >>> bandwidth that then gets converted back into some clock frequency? Do=
 we
> >>> have the user somewhere that can be pointed to?
> >> The clock rate is translated into a unitless threshold value sent as
> >> part of the rpmh msg
> >> that BCM takes to select a performance. In this case, the unit
> >> conversion is based on
> >> the unit value read from the aux data which is in Khz. I understand th=
at
> >> this wasn't
> >> explicitly mentioned anywhere and I'll improve on that next patch.
> > How is this different from bus bandwidth requests? In those cases the
> > bandwidth is calculated in bits per second or something like that, and
> > written to the hardware so it can convert that bandwidth into kHz and
> > set a bus clk frequency in the clock controller? So in the IPA case
> > we've skipped the bps to kHz conversion step and gone straight to the
> > clk frequency setting part? Is a BCM able to aggregate units of
> > bandwidth or kHz depending on how it's configured and this BCM is
> > configured for kHz?
> =

> The data written to the hardware is just a 14bit scalar value that it =

> takes to select a performance/frequency from a preset table. It's not =

> really doing any sort of conversion in hardware in this case, instead =

> the value is computed by software based on the aux data given. Think of =

> it as a generic aggregator as opposed to being strictly bandwidth and =

> the aggregator itself does not care what type of value it is(be it Khz =

> or BW/s).
> =


Got it. Thanks!