RE: [PATCH v6 04/11] firmware: xilinx: Add query data API

[Jolly Shah]

Hi Sudeep,

> -----Original Message-----
> From: Sudeep Holla [mailto:sudeep.holla@xxxxxxx]
> Sent: Tuesday, May 15, 2018 2:34 AM
> To: Jolly Shah <JOLLYS@xxxxxxxxxx>; ard.biesheuvel@xxxxxxxxxx;
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> mark.rutland@xxxxxxx; linux-clk@xxxxxxxxxxxxxxx
> Cc: Sudeep Holla <sudeep.holla@xxxxxxx>; Rajan Vaja <RAJANV@xxxxxxxxxx>;
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> Subject: Re: [PATCH v6 04/11] firmware: xilinx: Add query data API
> 
> 
> 
> On 14/05/18 20:16, Jolly Shah wrote:
> > HI Sudeep,
> >
> 
> [...]
> 
> >>
> >> Can you give more insight into this ? How will be this used ? How
> >> this aligns with data we get from DT ? I am just trying to understand
> >> how is this information split between this API and DT for example.
> >>
> >
> > This API is used to get clock information from firmware and register
> > clocks accordingly in driver. In our case, firmware maintains database
> > of all clocks available on chip. DT will provide information for off
> > chip reference clocks only. This is to avoid duplication of clocks
> > data in DT and firmware both as firmware anyways need clock data to
> > manage them.
> >
> 
> I wanted to understand the difference with example. What kind of information
> you get from DT and what you get from firmware ?
> 
> --
> Regards,
> Sudeep


Below is an example showing PLL and Leaf clock derivation:

Input ref clocks->Mux->Multiplier/Divider->PLL*
Pll1/pll2/pll3/pll4->Mux->Divider->Gate->Leaf clock1

Here Off chip input ref clock information comes from DT.
Rest information for Pll/leaf clocks come from firmware using query API. For clock driver, query API is used to get topology, flags, parents etc information per clock.

Thanks,
Jolly Shah