[linux-sunxi] Re: [PATCH v3 05/13] ARM: dts: sun9i: Add clock-indices property for bus gate clocks

[maxime.ripard@free-electrons.com (Maxime Ripard)]

On Thu, Jan 15, 2015 at 11:35:42PM +0800, Chen-Yu Tsai wrote:
> On Thu, Jan 15, 2015 at 11:20 PM, Maxime Ripard
> <maxime.ripard@free-electrons.com> wrote:
> > On Thu, Jan 15, 2015 at 10:24:04AM +0800, Chen-Yu Tsai wrote:
> >> On Thu, Jan 15, 2015 at 12:33 AM, Maxime Ripard
> >> <maxime.ripard@free-electrons.com> wrote:
> >> > On Tue, Jan 13, 2015 at 09:37:27AM +0800, Chen-Yu Tsai wrote:
> >> >> of_clk_get_parent_name() uses the clock-indices property to resolve
> >> >> clock phandle arguments in case that the argument index does not
> >> >> match the clock-output-names sequence.
> >> >>
> >> >> This is the case on sunxi, where we use the actual bit index as the
> >> >> argument to the phandle. Add the clock-indices property so that
> >> >> of_clk_get_parent_name() resolves the names correctly.
> >> >>
> >> >> Signed-off-by: Chen-Yu Tsai <wens@csie.org>
> >> >
> >> > Applied. Are the mask in the clock driver still of any use now? I
> >> > don't think they are, and if we're going that way, I'd rather have
> >> > them removed from the driver.
> >>
> >> Yes they are still passed through factors_data, for mux_clk_ops to
> >> know about the width of the mux, which is 3 bits on older SoCs vs
> >> 4 bits on sun9i.
> >
> > Erm.... These are gates. They are not muxable and are not handled
> > through clk-factors, so I'm not sure how it is relevant :)
> 
> Sorry. I jumped to the mux mask stuff. Yes the gate masks are still
> used, and the gates are still referenced by the bit offset.
> 
> As described in the commit message, clock-indices is used by
> of_clk_get_parent_name() to match the index used in the phandle
> to the correct name in clock-names.
> 
> Take apb1 for example:
> 
>                        clock-indices = <0>, <1>, <2>, <3>, <4>,
>                                        <16>, <17>, <18>, <19>, <20>, <21>;
>                        clock-output-names = "apb1_i2c0", "apb1_i2c1",
>                                        "apb1_i2c2", "apb1_i2c3", "apb1_i2c4",
>                                        "apb1_uart0", "apb1_uart1", ...
> 
> If we have "clocks = <&apb1 16>;" in some device, and we call
> of_clk_get_parent_name() on said clock, it would try to get
> clock_output_names[16], which obviously is the wrong one.
> 
> With clock-indices, of_clk_get_parent_name first looks at
> that array, finds an entry matching 16, then uses the
> index of the matching entry to get the name from
> clock-output-names.

Yeah, I know what it does, and we do agree on the fact that it's
needed.

> So, we are still using the gate bitmask to declare valid
> clock gates. The sunxi driver does not use clock-indices
> directly. Nor do I think it was intended to be used by
> clock drivers directly.

However, the gate bitmask itself carries exactly the same information
than clock-indices. It's the exact same list of numbers, just with two
different ways of defining it.

If we go with clock-indices, which is the right solution, then we can
just drop the other one.

I actually started to do just this last evening. A31 boots without any
gates bit mask but the USB clocks one so far, I intend on converting
the others as well.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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