Hi Thomas, Lukasz,
Let me put my two cents in.
On 11.01.2014 05:43, Thomas Abraham wrote:
On Fri, Jan 10, 2014 at 6:55 PM, Lukasz Majewski <l.majewski@xxxxxxxxxxx> wrote:
Hi Thomas,
Hi Lukasz,
On Fri, Jan 10, 2014 at 5:34 PM, Lukasz Majewski
<l.majewski@xxxxxxxxxxx> wrote:
[snip]
+/* 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.
Still, separation between clock drivers and clock providers would be
nice. clk-exynos4.c and friends doesn't implement any clock handling
logic, they just define the tree of available clocks. I agree with
Lukasz that separate file would be better place for such code, just as
it was done with PLL drivers.
In addition this would allow you to make the generic core clock helpers
static, as they could be moved to the same file where all the core clock
driver variants are implemented.
Moreover, maybe you can choose a shorter name?
Ok, I will try to find a shorter name for in the next version.
I'm not sure how the name (or which name) could be shorter here, without
impairing readability. Lukasz, can you elaborate?
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.
I don't think the core clock is going to be used (in reconfigurable way)
with anything else than cpufreq. I agree with Thomas, though, that clock
drivers should not have any dependencies on other subsystems. Separation
is always good.
However, Lukasz has a valid point. Your patch is adding third place
where list of CPU frequencies is defined. We really shouldn't have
allowed this to be scattered into two pieces with common clock framework
implementation, not even saying about three. This is data redundancy
that is not only error prone, but also a maintenance issue, because
whenever one wants to change the set of supported frequencies, they must
modify all two (or three) locations.
My stance on this is that we should get rid of this redundancy and I
won't Ack any patch that makes us further from this goal, unless you can
convince me that there is no other option.
As for how I see solution for this, I believe that possible APLL
settings, core clock settings and cpufreq operating points are all
board-specific or at least SoC revision-specific. Moreover, they are all
closely related to themselves:
- the list of available cpufreq operating points depends on available
APLL and core clock configurations,
- each APLL setting has its own, specific, set of configurations of
core dividers.
This makes me almost sure that what we want is a single place where all
(or at least all clock-related) data are specified and this is probably
device tree, since those can be board-specific or at least SoC revision
specific.
+
+/**
+ * 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.
Those values aren't really such generic as one might think. There exist
different SoC revisions on which different settings can be used.
Moreover, I've already seen different sets of settings even for the same
board in different sources of vendor kernel. This might mean that those
values are in fact more of configuration, than static values selected
for given hardware.
Best regards,
Tomasz
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