linux-kernel - Re: [PATCH 3/6] clk: actions: Fix bisp_factor

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Date:   Tue, 16 Mar 2021 20:37:53 +0200
From:   Cristian Ciocaltea <cristian.ciocaltea@...il.com>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Cc:     Stephen Boyd <sboyd@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Andreas Färber <afaerber@...e.de>,
        Michael Turquette <mturquette@...libre.com>,
        Edgar Bernardi Righi <edgar.righi@...tec.org.br>,
        linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-actions@...ts.infradead.org, linux-kernel@...r.kernel.org,
        devicetree@...r.kernel.org
Subject: Re: [PATCH 3/6] clk: actions: Fix bisp_factor_table based clocks on
 Owl S500 SoC

On Tue, Mar 16, 2021 at 09:47:39AM +0530, Manivannan Sadhasivam wrote:
> On Mon, Mar 08, 2021 at 07:18:28PM +0200, Cristian Ciocaltea wrote:
> > The following clocks of the Actions Semi Owl S500 SoC have been defined
> > to use a shared clock factor table 'bisp_factor_table[]': DE[1-2], VCE,
> > VDE, BISP, SENSOR[0-1]
> > 
> > There are several issues involved in this approach:
> > 
> > * 'bisp_factor_table[]' describes the configuration of a regular 8-rates
> >   divider, so its usage is redundant. Additionally, judging by the BISP
> >   clock context, it is incomplete since it maps only 8 out of 12
> >   possible entries.
> > 
> > * The clocks mentioned above are not identical in terms of the available
> >   rates, therefore cannot rely on the same factor table. Specifically,
> >   BISP and SENSOR* are standard 12-rate dividers so their configuration
> >   should rely on a proper clock div table, while VCE and VDE require a
> >   factor table that is a actually a subset of the one needed for DE[1-2]
> >   clocks.
> > 
> > Let's fix this by implementing the following:
> > 
> > * Add new factor tables 'de_factor_table' and 'hde_factor_table' to
> >   properly handle DE[1-2], VCE and VDE clocks.
> > 
> > * Add a common div table 'std12rate_div_table' for BISP and SENSOR[0-1]
> >   clocks converted to OWL_COMP_DIV.
> > 
> > * Drop the now unused 'bisp_factor_table[]'.
> > 
> 
> Nice!
> 
> > Additionally, since SENSOR[0-1] are not gated, unset the OWL_GATE_HW
> > configuration and drop the CLK_IGNORE_UNUSED flag in their definitions.
> > 
> 
> No. You should not screen the functionality exposed by the hw, that's what the
> purpose of these CLK_ flags.

I'm not sure I get this, or maybe I wasn't clear enough with my
explanation regarding the changes to SENSOR clocks: they are not gated
in hardware, hence the statement 'OWL_GATE_HW(CMU_DEVCLKEN0, 14, 0)' 
was invalid and I replaced it with '{ 0 }'.

Additionally, I assumed the 'CLK_IGNORE_UNUSED' flag makes sense only
for the gated clocks. Do I miss something?

> Other than that, this patch looks good to me.

Thanks,
Cristi

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