linux-kernel - Re: [PATCH 2/6] clk: meson: add a driver for the Meson8/8b/8m2 DDR clock controller

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Date:   Tue, 1 Oct 2019 20:53:59 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Jerome Brunet <jbrunet@...libre.com>
Cc:     Neil Armstrong <narmstrong@...libre.com>,
        linux-amlogic@...ts.infradead.org, devicetree@...r.kernel.org,
        khilman@...libre.com, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-clk@...r.kernel.org
Subject: Re: [PATCH 2/6] clk: meson: add a driver for the Meson8/8b/8m2 DDR
 clock controller

Hi Jerome,

thank you for taking the time to go through this!

On Tue, Oct 1, 2019 at 3:29 PM Jerome Brunet <jbrunet@...libre.com> wrote:
[...]
> > +#include <linux/platform_device.h>
> > +#include <linux/mfd/syscon.h>
>
> syscon is not used in the driver
oops, good catch - thank you

[...]
> > +static struct clk_hw_onecell_data meson8_ddr_clk_hw_onecell_data = {
> > +     .hws = {
> > +             [DDR_CLKID_DDR_PLL_DCO]         = &meson8_ddr_pll_dco.hw,
> > +             [DDR_CLKID_DDR_PLL]             = &meson8_ddr_pll.hw,
>
> I wonder if onecell is not overkill for this driver. We won't expose the
> DCO, so only the post divider remains
>
> Do you expect this provider to have more than one leaf clock ?
> If not, maybe you could use of_clk_hw_simple_get() instead ?
there's some more clock bits in DDR_CLK_CNTL - the public A311D
datasheet has a description for these bits but I'm not sure they do
the same on Meson8/Meson8b/Meson8m2
all I know is that some magic bytes are written to DDR_CLK_CNTL in the
old u-boot code

that's why I don't want to make any assumptions and play safe here (by
using a onecell clock provider)

> > +     },
> > +     .num = 2,
> > +};
> > +
> > +static struct clk_regmap *const meson8_ddr_clk_regmaps[] = {
> > +     &meson8_ddr_pll_dco,
> > +     &meson8_ddr_pll,
> > +};
> > +
> > +static const struct regmap_config meson8_ddr_clkc_regmap_config = {
> > +     .reg_bits = 8,
> > +     .val_bits = 32,
> > +     .reg_stride = 4,
> > +     .fast_io = true,
>
> I think fast_io will default to true with memory based register.
> Setting the max_register would be nice
good point - I'll take care of this when sending v2


Martin