Re: [PATCH 2/6] clk: samsung: add infrastructure to register CPU clocks

Thomas Abraham
2014-01-11T04:43:47Z

On Fri, Jan 10, 2014 at 6:55 PM, Lukasz Majewski <l.majewski@samsung.com> wrote:
> Hi Thomas,
>
>> Hi Lukasz,
>>
>> On Fri, Jan 10, 2014 at 5:34 PM, Lukasz Majewski
>> <l.majewski@samsung.com> wrote:
>> > Hi Thomas,
>> >
>> >> The CPU clock provider supplies the clock to the CPU clock domain.
>> >> The composition and organization of the CPU clock provider could
>> >> vary among Exynos SoCs. A CPU clock provider can be composed of
>> >> clock mux, dividers and gates. This patch defines a new clock type
>> >> for CPU clock provider and adds infrastructure to register the CPU
>> >> clock providers for Samsung platforms.
>> >>
>> >> Signed-off-by: Thomas Abraham <thomas.ab@samsung.com>
>> >> ---
>> >> drivers/clk/samsung/clk.c | 71
>> >> +++++++++++++++++++++++++++++++++++++++++++++
>> >> drivers/clk/samsung/clk.h | 37 +++++++++++++++++++++++- 2 files
>> >> changed, 107 insertions(+), 1 deletions(-)
>> >>
>> >> diff --git a/drivers/clk/samsung/clk.c b/drivers/clk/samsung/clk.c
>> >> index f503f32..9ac9056 100644
>> >> --- a/drivers/clk/samsung/clk.c
>> >> +++ b/drivers/clk/samsung/clk.c
>> >> @@ -316,3 +316,74 @@ unsigned long _get_rate(const char *clk_name)
>> >>
>> >> return clk_get_rate(clk);
>> >> }
>> >> +
>> >> +/*
>> >> + * On most platform, the core clock rate is equal to the clock
>> >> rate of
>> >> + * parent pll. This is a simple helper function to support
>> >> recalc_rate
>> >> + * callback for such platforms.
>> >> + */
>> >> +unsigned long samsung_core_clock_recalc_rate(struct clk_hw *hw,
>> >> + unsigned long parent_rate)
>> >> +{
>> >> + /*
>> >> + * Assuming that the output of the parent pll is the output
>> >> clock
>> >> + * frequency of the core clock.
>> >> + */
>> >> + return parent_rate;
>> >> +}
>> >> +
>> >> +/* This is a helper function to perform clock rounding for core
>> >> clocks. */ +long samsung_core_clk_round_rate(struct clk_hw *hw,
>> >> + unsigned long drate, unsigned long *prate)
>> >> +{
>> >> + struct samsung_core_clock *core_clk;
>> >> + const struct samsung_core_clock_freq_table *freq_tbl;
>> >> + int i;
>> >> +
>> >> + core_clk = container_of(hw, struct samsung_core_clock, hw);
>> >> + freq_tbl = core_clk->freq_table;
>> >> + drate /= 1000;
>> >> +
>> >> + for (i = 0; i < freq_tbl->freq_count; i++) {
>> >> + if (drate >= freq_tbl->freq[i])
>> >> + return freq_tbl->freq[i] * 1000;
>> >> + }
>> >> + return freq_tbl->freq[i - 1] * 1000;
>> >> +}
>> >> +
>> >> +/* helper function to register a core clock */
>> >> +void __init samsung_coreclk_register(const char *name, const char
>> >> **parents,
>> >> + unsigned int num_parents, const char *pllclk,
>> >> + const struct clk_ops *clk_ops, unsigned int
>> >> lookup_id,
>> >> + const struct samsung_core_clock_freq_table
>> >> *freq_tbl) +{
>> >> + struct samsung_core_clock *coreclk;
>> >> + struct clk_init_data init;
>> >> + struct clk *clk;
>> >> +
>> >> + coreclk = kzalloc(sizeof(*coreclk), GFP_KERNEL);
>> >> + if (!coreclk) {
>> >> + pr_err("%s: could not allocate memory for coreclk
>> >> %s\n",
>> >> + __func__, name);
>> >> + return;
>> >> + }
>> >> +
>> >> + init.name = name;
>> >> + init.flags = CLK_GET_RATE_NOCACHE;
>> >> + init.parent_names = parents;
>> >> + init.num_parents = num_parents;
>> >> + init.ops = clk_ops;
>> >> +
>> >> + coreclk->hw.init = &init;
>> >> + coreclk->ctrl_base = reg_base;
>> >> + coreclk->fout_pll = __clk_lookup(pllclk);
>> >> + coreclk->freq_table = freq_tbl;
>> >> +
>> >> + clk = clk_register(NULL, &coreclk->hw);
>> >> + if (IS_ERR(clk)) {
>> >> + pr_err("%s: could not register coreclk %s\n",
>> >> __func__, name);
>> >> + kfree(coreclk);
>> >> + return;
>> >> + }
>> >> + samsung_clk_add_lookup(clk, lookup_id);
>> >> +}
>> >
>> > I think, that those definitions for samsung_core_clock shall be
>> > moved to a separate file (maybe clk-exynos-cpu.c)?
>>
>> The additions were not really much and the samsung/clk.c file is used
>> to hold all the common code for Samsung SoCs. So the additions were
>> put into this existing file itself.
>>
>> >
>> > Moreover, maybe you can choose a shorter name?
>>
>> Ok, I will try to find a shorter name for in the next version.
>>
>> >
>> >> diff --git a/drivers/clk/samsung/clk.h b/drivers/clk/samsung/clk.h
>> >> index 31b4174..0e43023 100644
>> >> --- a/drivers/clk/samsung/clk.h
>> >> +++ b/drivers/clk/samsung/clk.h
>> >> @@ -312,6 +312,37 @@ struct samsung_pll_clock {
>> >> __PLL(_typ, _id, NULL, _name, _pname,
>> >> CLK_GET_RATE_NOCACHE, \ _lock, _con, _rtable, _alias)
>> >>
>> >> +/**
>> >> + * struct samsung_core_clock_freq_table: table of frequency
>> >> supported by
>> >> + * a core clock and associated data if any.
>> >> + * @freq: points to a table of supported frequencies (in KHz)
>> >> + * @freq_count: number of entries in the frequency table
>> >> + * @data: core clock specific data, if any
>> >> + */
>> >> +struct samsung_core_clock_freq_table {
>> >> + const unsigned long *freq; /* in KHz */
>> >> + unsigned long freq_count;
>> >> + const void *data;
>> >> +};
>> >
>> > This is another instance of a structure, which holds the frequency
>> > for the system (like struct cpufreq_frequency_table).
>> >
>> > Unfortunately, since the clk subsystem starts very early, the
>> > cpufreq_frequency_table is not yet parsed from "operating-points"
>> > attribute.
>> >
>> > Maybe we can defer the clock registration?
>>
>> The core clock is not limited to support only those frequencies which
>> the CPU operating point specifies. The core clock type can be used
>> independent of the cpufreq driver and hence has its own set of
>> supported frequencies. The cpufreq driver, depending the operating
>> points allowed, can request the core clock to setup the requested
>> clock speed.
>
> The above would be true if it could have been possible to use this
> clock without cpufreq.
>
> Since, justification of this whole change is the clean up of cpufreq for
> Exynos, I assume that it will be only used with cpufreq. Is there any
> use case to use this clock without cpufreq?
>
> For this reason Exynos SoCs can only change frequency to the one, which
> is defined at cpufreq_frequency_table.
>
> And since the cpufreq_frequency_table is dynamically build from
> operating-points attribute, then in my opinion we shall refer to only
> one place for frequency.
>
> Similar approach - of reusing cpufreq_frequency_table is used at
> thermal core driver.

One of the reasons for keeping the supported frequencies independent
of the cpufreq table was ensure that platforms are free to use only a
subset of the supported clock speed due to certain performance/power
requirements particular to that platform Two or more platforms based
on the same SoC can have different power/performance requirements. The
case of thermal is different, it can only request for the CPU to be
clocked at speeds supported by the cpufreq driver.

Also, the core clock type is not limited to be used only by the
cpufreq driver. It should be possible to use a platform without the
cpufreq driver but still have the flexibility to change the cpu clock
speed.

>
>>
>> >
>> >> +
>> >> +/**
>> >> + * struct samsung_core_clock: information about clock supplied to
>> >> a CPU core.
>> >> + * @hw: handle between ccf and core clock.
>> >> + * @ctrl_base: base address of the clock controller.
>> >> + * @fout_pll: clock handle representing the clock output of the
>> >> associated PLL.
>> >> + */
>> >> +struct samsung_core_clock {
>> >> + struct clk_hw hw;
>> >> + void __iomem *ctrl_base;
>> >> + struct clk *fout_pll;
>> >> + const struct samsung_core_clock_freq_table *freq_table;
>> >> +};
>> >> +
>> >> +extern unsigned long samsung_core_clock_recalc_rate(struct clk_hw
>> >> *hw,
>> >> + unsigned long parent_rate);
>> >> +extern long samsung_core_clk_round_rate(struct clk_hw *hw,
>> >> + unsigned long drate, unsigned long *prate);
>> >
>> > IMHO, those methods shall be defined as static in a separate file.
>>
>> These two functions are generic enough to be reused for core clock
>> implementations on multiple exynos platforms.
>
> I thought that you are going to implement this clock in a generic way,
> so by using the DT we could use it for Exynos4210/4x12 and 5250.
>
>> Only the set_rate
>> callback is the one that will be specific to SoC and core clock. The
>> SoC specific implementation can reuse these two callback funcitons
>> when registering the core clock type. That is the reason these are not
>> static functions. The 3/6 patch of this series includes the usage of
>> these functions.
>
> In my opinion we shall not duplicate per SoC constructs like for
> example:
>
> static struct apll_freq apll_freq_4412[]
> static struct apll_freq apll_freq_4212[]
> static struct apll_freq apll_freq_4210[]
>
> which would be used at different ->set_rate() callbacks.
>
> I think that the best solution would be to use one ->set_rate() with
> data parsed from DT.

Yes, I agree with you. The ->set_rate() callback code is not going to
be repeated if the code can be reused for other Exynos SoCs.

And about the values of the registers for set_rate coming in from DT,
these are SoC specific values and are not different for two or more
platforms using the same SoC. So why put this into DT? The same was
the argument about populating all the clocks from DT. Clock blocks are
not going to change from one platform to another platform which use
the same SoC. They are SoC specific and not platform specific and
hence there is little use in putting them into DT.

>
>>
>> Thanks,
>> Thomas.
>>
>> >
>> >> +
>> >> extern void __init samsung_clk_init(struct device_node *np, void
>> >> __iomem *base, unsigned long nr_clks, unsigned long *rdump,
>> >> unsigned long nr_rdump, unsigned long *soc_rdump,
>> >> @@ -337,7 +368,11 @@ extern void __init samsung_clk_register_gate(
>> >> struct samsung_gate_clock *clk_list, unsigned int
>> >> nr_clk); extern void __init samsung_clk_register_pll(struct
>> >> samsung_pll_clock *pll_list, unsigned int nr_clk, void __iomem
>> >> *base); -
>> >> +extern void __init samsung_coreclk_register(const char *coreclk,
>> >> + const char **parents, unsigned int num_parents,
>> >> + const char *pllclk, const struct clk_ops *clk_ops,
>> >> + unsigned int lookup_id,
>> >> + const struct samsung_core_clock_freq_table
>> >> *freq_tbl); extern unsigned long _get_rate(const char *clk_name);
>> >>
>> >> #endif /* __SAMSUNG_CLK_H */
>> >
>> >
>> >
>> > --
>> > Best regards,
>> >
>> > Lukasz Majewski
>> >
>> > Samsung R&D Institute Poland (SRPOL) | Linux Platform Group
>
>
>
> --
> Best regards,
>
> Lukasz Majewski
>
> Samsung R&D Institute Poland (SRPOL) | Linux Platform Group