Re: [PATCH v5 02/44] clk: davinci: New driver for davinci PLL clocks

[David Lechner]

On 01/12/2018 03:21 AM, Sekhar Nori wrote:
> On Monday 08 January 2018 07:47 AM, David Lechner wrote:
> > This adds a new driver for mach-davinci PLL clocks. This is porting the
> > code from arch/arm/mach-davinci/clock.c to the common clock framework.
> > Additionally, it adds device tree support for these clocks.
> >
> > The ifeq ($(CONFIG_COMMON_CLK), y) in the Makefile is needed to prevent
> > compile errors until the clock code in arch/arm/mach-davinci is removed.
> >
> > Note: although there are similar clocks for TI Keystone we are not able
> > to share the code for a few reasons. The keystone clocks are device tree
> > only and use legacy one-node-per-clock bindings. Also the register
> > layouts are a bit different, which would add even more if/else mess
> > to the keystone clocks. And the keystone PLL driver doesn't support
> > setting clock rates.
> >
> > Signed-off-by: David Lechner <david@xxxxxxxxxxxxxx>
> > ---

> > +
> > +#define PLLM_MASK		0x1f
> > +#define PREDIV_RATIO_MASK	0x1f
>
> May be use the mode modern GENMASK()?

I haven't seen that one before. Thanks.

...

> > +static unsigned long davinci_pll_clk_recalc(struct clk_hw *hw,
> > +					    unsigned long parent_rate)
> > +{
> > +	struct davinci_pll_clk *pll = to_davinci_pll_clk(hw);
> > +	unsigned long rate = parent_rate;
> > +	u32 prediv, mult, postdiv;
> > +
> > +	prediv = readl(pll->base + PREDIV) & PREDIV_RATIO_MASK;
> > +	mult = readl(pll->base + PLLM) & PLLM_MASK;
> > +	postdiv = readl(pll->base + POSTDIV) & POSTDIV_RATIO_MASK;
>
> Shouldn't we check if the pre and post dividers are enabled before using
> them?

Indeed.

> > +
> > +	rate /= prediv + 1;
> > +	rate *= mult + 1;
> > +	rate /= postdiv + 1;
> > +
> > +	return rate;
> > +}
> > +

...

> PLL output on DA850 must never be below 300MHz or above 600MHz (see
> datasheet table "Allowed PLL Operating Conditions"). Does this take care
> of that? Thats one of the main reasons I recall I went with some
> specific values of prediv, pllm and post div in
> arch/arm/mach-davinci/da850.c

Apparently, I missed this requirement. It looks like I am going to have to
rework things so that there is some coordination between the PLL and the
PLLDIV clocks in order to get the < 300MHz operating points.

...

> > +
> > +	divider->reg = base + OSCDIV;
> > +	divider->width = OSCDIV_RATIO_WIDTH;
>
> can you write OD1EN of OSCDIV here? I guess the reset default is 1 so
> you didnt need to do that. But not doing exposes us to settings that
> bootloader left us in.

It looks like I am going to have to make a custom implementation for parts
of this clock anyway, so I will probably just make new enable/disable
callbacks that set both OSCDIV_OD1EN and CKEN_OBSCLK.

> > +
> > +	clk = clk_register_composite(NULL, name, parent_names, num_parents,
> > +				     &mux->hw, &clk_mux_ops,
> > +				     &divider->hw, &clk_divider_ops,
> > +				     &gate->hw, &clk_gate_ops, 0);
> > +	if (IS_ERR(clk)) {
> > +		kfree(divider);
> > +		kfree(gate);
> > +		kfree(mux);
> > +	}
> > +
> > +	return clk;
> > +}
> > +
> > +struct clk *
> > +davinci_pll_divclk_register(const struct davinci_pll_divclk_info *info,
> > +			    void __iomem *base)
> > +{
> > +	const struct clk_ops *divider_ops = &clk_divider_ops;
>
> setting the sysclk divider requires GOSTAT handling apart from setting
> the divider value. So I think .set_rate ops above wont work. Other ops
> can be used, I guess. So we need a private structure here.
>
> Can you port over davinci_set_sysclk_rate() too? I understand you cannot
> test it due to lack of cpufreq support in DT, but I can help testing there.
>
> Or leave .set_rate NULL and it can be added later.

Yes, I noticed that I missed this after I submitted this series. And I
will have to rework things to coordinate with the PLL as mentioned above.

FYI, I do have cpufreq-dt working, although the LEGO EV3 has a fixed 1.2V
regulator, so I am limited in what I can test. Basically, I can only switch
between 300MHz and 375MHz according to the datasheets. The chip is technically
the 456MHz version. What would happen if I ran it faster or slower with the
wrong voltage?

...

> > +
> > +	child = of_get_child_by_name(node, "auxclk");
> > +	if (child && of_device_is_available(child)) {
> > +		char child_name[MAX_NAME_SIZE];
> > +
> > +		snprintf(child_name, MAX_NAME_SIZE, "%s_aux_clk", name);
> > +
> > +		clk = davinci_pll_aux_clk_register(child_name, parent_name, base);
> > +		if (IS_ERR(clk))
> > +			pr_warn("%s: failed to register %s (%ld)\n", __func__,
> > +				child_name, PTR_ERR(clk));
> > +		else
> > +			of_clk_add_provider(child, of_clk_src_simple_get, clk);
> > +	}
>
> davinci_pll_obs_clk_register() should also be handled here?

I omitted it because no one is using it (same reason I left it out of the
device tree bindings). We can certainly add it, though.