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

From: wens@csie.org (Chen-Yu Tsai)
To: linux-arm-kernel@lists.infradead.org
Subject: [linux-sunxi] Re: [PATCH v3 05/13] ARM: dts: sun9i: Add clock-indices property for bus gate clocks
Date: Fri, 16 Jan 2015 00:09:01 +0800	[thread overview]
Message-ID: <CAGb2v67x=NP8SX9bLqvKg-=-TM4EwU3fNppaxo0HP7fO=gDGjw@mail.gmail.com> (raw)
In-Reply-To: <20150115155156.GA1837@lukather>

On Thu, Jan 15, 2015 at 11:51 PM, Maxime Ripard
<maxime.ripard@free-electrons.com> wrote:
> 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.

So as I understand, you want to replace the masks in the clock drivers
with clock-indices in the dt. Is this correct? This potentially makes
the gates clock driver very generic, which is nice.

I only see drivers/clk/shmobile/clk-mstp.c using it this way though.
Didn't we have this for sun6i-apb0-gates at one time?

I'm not against it. Just want to make sure everyone agrees, and we
can work who and how we're going about this.

Thanks
ChenYu