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

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Message-ID: <20210526101830.GE10723@work>
Date:   Wed, 26 May 2021 15:48:30 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Cristian Ciocaltea <cristian.ciocaltea@...il.com>
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 08:37:53PM +0200, Cristian Ciocaltea wrote:
> 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 }'.
> 

This clock is gated in hw as per the datasheet. Again, please don't make
judgements based on the vendor code as it is not upto date with HW. I
know it is silly but that's how things are...

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

CLK_IGNORE_UNUSED is used by the clk framework to essentially skip
gating the clocks which are turned ON by the bootloader and there is no
other driver using it. But I think you can remove this flag because
there is no reason to leave this specific clock to be ON always.

Thanks,
Mani

> > Other than that, this patch looks good to me.
> 
> Thanks,
> Cristi
> 
> [...]