[PATCH v2 1/5] clk: samsung: add common clock framework support for Samsung platforms

[Thomas Abraham]

Hi Sylwester,

On 31 October 2012 04:40, Sylwester Nawrocki
<sylvester.nawrocki at gmail.com> wrote:
> Hi Thomas,
>
> On 10/29/2012 11:09 AM, Thomas Abraham wrote:
>> Hi Sylwester,
>>
>> Thanks for your comments. As usual, your comments are very helpful.
>
> Thanks.
>> On 22 October 2012 21:25, Sylwester Nawrocki<s.nawrocki at samsung.com>  wrote:
>>> Hi Thomas,
>>>
>>> On 10/07/2012 07:10 PM, Thomas Abraham wrote:
>>>> All Samsung platforms include several types of clocks including fixed-rate,
>>>> mux, divider and gate clock types. There are typically hundreds of such clocks
>>>> on each of the Samsung platforms. To enable Samsung platforms to register these
>>>> clocks using the common clock framework, a bunch of utility functions are
>>>> introduced here which simplify the clock registration process.
>>>>
>>>> In addition to the basic types of clock supported by common clock framework,
>>>> a Samsung specific representation of the PLL clocks is also introduced.
>>>>
>>>> Both legacy and device tree based Samsung platforms are supported. On legacy
>>>> platforms, the clocks are statically instantiated and registered with common
>>>> clock framework. On device tree enabled platforms, the device tree is
>>>> searched and all clock nodes found are registered. It is also possible to
>>>> register statically instantiated clocks on device tree enabled platforms.
>>>>
>>>> Cc: Mike Turquette<mturquette at ti.com>
>>>> Cc: Kukjin Kim<kgene.kim at samsung.com>
>>>> Signed-off-by: Thomas Abraham<thomas.abraham at linaro.org>
>>>
>>> Thanks for the patch. I'm trying to use this series on an Exynos4412
>>> SoC based board. I think it wasn't tested with Exynos4x12 (with FDT
>>> support), was it ?
>>
>> No, it has not been tested on any Exynos4x12 based board. I have
>> tested it only for Exynos4210 based origen board.
>
> OK, thanks. I've had some issues with the root clocks on Exynos4412
> and I put this on a back burner for a while. I plan to get back to
> this, possibly after ELCE/LinuxCon.

Ok.

>
>>>> ---
>>>>   drivers/clk/Makefile         |    1 +
>>>>   drivers/clk/samsung/Makefile |    5 +
>>>>   drivers/clk/samsung/clk.c    |  414 ++++++++++++++++++++++++++++++++++++++++++
>>>>   drivers/clk/samsung/clk.h    |  212 +++++++++++++++++++++
>>>>   4 files changed, 632 insertions(+), 0 deletions(-)
>>>>   create mode 100644 drivers/clk/samsung/Makefile
>>>>   create mode 100644 drivers/clk/samsung/clk.c
>>>>   create mode 100644 drivers/clk/samsung/clk.h
> ...
>>>> +/* register a samsung pll type clock */
>>>> +void __init samsung_clk_register_pll(const char *name, const char **pnames,
>>>> +                             struct device_node *np,
>>>> +                             int (*set_rate)(unsigned long rate),
>>>> +                             unsigned long (*get_rate)(unsigned long rate))
>>>> +{
>>>> +     struct samsung_pll_clock *clk_pll;
>>>> +     struct clk *clk;
>>>> +     struct clk_init_data init;
>>>> +     int ret;
>>>> +
>>>> +     clk_pll = kzalloc(sizeof(*clk_pll), GFP_KERNEL);
>>>> +     if (!clk_pll) {
>>>> +             pr_err("%s: could not allocate pll clk %s\n", __func__, name);
>>>> +             return;
>>>> +     }
>>>> +
>>>> +     init.name = name;
>>>> +     init.ops =&samsung_pll_clock_ops;
>>>> +     init.flags = CLK_GET_RATE_NOCACHE;
>>>> +     init.parent_names = pnames;
>>>> +     init.num_parents = 1;
>>>> +
>>>> +     clk_pll->set_rate = set_rate;
>>>> +     clk_pll->get_rate = get_rate;
>>>> +     clk_pll->hw.init =&init;
>>>> +
>>>> +     /* register the clock */
>>>> +     clk = clk_register(NULL,&clk_pll->hw);
>>>> +     if (IS_ERR(clk)) {
>>>> +             pr_err("%s: failed to register pll clock %s\n", __func__,
>>>> +                             name);
>>>> +             kfree(clk_pll);
>>>> +             return;
>>>> +     }
>>>> +
>>>> +#ifdef CONFIG_OF
>>>> +     if (np)
>>>> +             of_clk_add_provider(np, of_clk_src_simple_get, clk);
>>>> +#endif
>>>
>>> Is it really required to do clk_register() and of_clk_add_provider() for
>>> each single clock ? This seems more heavy than it could be. Looking at
>>
>> of_clk_add_provider call for every clock instance is not really
>> required but it does allow platform code to lookup the clock and
>> retrieve/display the clock speed. That was the intention to add a
>> lookup for all the clocks.
>
> Hmm, do you mean calling clk_get() with NULL 'dev' argument ?
> It's probably not a big deal to look up the clocks root node and
> then use of_clk_get() function to find required clock ?

Yes, I was referring to calling clk_get() with NULL 'dev' argument.
Usually, at boot, the clock frequency of some of the system clocks
(such as aclk_200) are displayed. So all the clocks were registered
using clk_register allowing clock frequency of any the clock to be
retrieved using clk_get.

Your suggestion to use of_clk_get assumes the clock implementation
follows the imx style, which was not way used in this patch series.
And then there is this problem of supporting non-dt platforms as well.

>
>>> drivers/clk/mxs/clk-imx28.c, it registers only single clock provider for
>>> whole group of clocks. Also, couldn't we statically define most of the
>>> clocks and still register them so they can be used with platforms using
>>> FDT ? Something along the lines of imx28 implementation (arch/arm/boot/dts
>>> /imx28.dtsi), where a clock is specified at consumer device node by
>>> a phandle to the clock controller node and a clock index ?
>>
>> We could do it that way. I was tempted to list out all the clocks in
>> device tree and then register them so that there is no static
>> definition of the clocks needed. You seem to prefer not to do that. I
>> am fine with either way, static or device tree based registration.
>
> Ok, it's also worth noting that clk_get() would have been more expensive
> when there would be a need to iterate over large number of clock providers.
> Indexed look up might be a better alternative.

Yes, true.

>
> Exynos SoCs have fairly complex clock tree structure, I personally do find
> it harder to understand from a bit bulky description in form of a device
> tree node list. Comparing to the original Samsung clock API there is now
> more clock objects, since, e.g. single struct clk_clksrc is now represented
> by mux, div and gate clock group, which makes things slightly more
> complicated, i.e. there is even more clocks to be listed.
>

Ok.

>>> Besides that, what bothers me with in the current approach is the
>>> clock consumers being defined through one big data structure together
>>> with the actual clocks. Not all clock objects are going to have
>>> consumers, some resources are waisted by using flat tables of those
>>> big data structure objects. Perhaps we could use two tables, one for the
>>> platform clocks and one for the consumers ? These common clock driver
>>> is intended to cover all Samsung SoC, I would expect all samsung
>>> sub-archs getting converted to use it eventually, with as many of them
>>> as possible then reworked to support device tree. It's a lot of work
>>> and is going to take some time, but it would be good to have it planned
>>> in advance. That said I'm not sure the common samsung clock driver in
>>> non-dt variant would be really a temporary thing.
>>
>> Non-dt support in Samsung common clock driver will be maintained. But
>> for existing Exynos4 non-dt platforms, it should be possible to
>> convert them to completely device tree based platforms.
>
> OK, let's then focus on device tree support for exynos4+ SoCs. I hope we
> could have the clocks statically defined and still freely accessible in
> the device tree.

Ok. I will implement it as you mentioned.

>
>>>> +     /*
>>>> +      * Register a clock lookup for the pll-type clock even if this
>>>> +      * has been instantiated from device tree. This helps to do
>>>> +      * clk_get() lookup on this clock for pruposes of displaying its
>>>> +      * clock speed at boot time.
>>>> +      */
>>>> +     ret = clk_register_clkdev(clk, name, NULL);
>>>> +     if (ret)
>>>> +             pr_err("%s: failed to register clock lookup for %s", __func__,
>>>> +                             name);
>>>> +}
> ...
>>>> +
>>>> +#ifdef CONFIG_OF
>>>> +/* register a samsung gate type clock instantiated from device tree */
>>>> +void __init samsung_of_clk_register_gate(struct device_node *np)
>>>> +{
>>>> +     struct samsung_gate_clock clk_gate;
>>>> +     const char *clk_name = np->name;
>>>> +     const char *parent_name;
>>>> +     u32 reg_info[2];
>>>> +
>>>> +     of_property_read_string(np, "clock-output-names",&clk_name);
>>>> +     parent_name = of_clk_get_parent_name(np, 0);
>>>> +     if (of_property_read_u32_array(np, "reg-info", reg_info, 2))
>>>> +             pr_err("%s: invalid register info in node\n", __func__);
>>>> +
>>>> +     clk_gate.name = clk_name;
>>>> +     clk_gate.parent_name = parent_name;
>>>> +     clk_gate.reg = (void __iomem *)(reg_base + reg_info[0]);
>>>> +     clk_gate.bit_idx = reg_info[1];
>>>> +     clk_gate.dev_name = NULL;
>>>> +     clk_gate.flags = 0;
>>>> +     clk_gate.gate_flags = 0;
>>>
>>> Some clocks need CLK_SET_RATE_PARENT for the drivers to work
>>> as before. So far it is not set for any mux, div nor gate clock.
>>
>> Ok. I will fix this.
>>
>> So about the static vs device tree based clock registration, what
>> would you suggest?
>
> Defining the clocks statically has my preference, it would be nice to
> hear more opinions on that though. I think on a heavily utilised SoC
> the list of clock nodes could have grown significantly. And with
> preprocessor support at the dt compiler (not sure if it is already
> there) indexed clock definitions could be made more explicit.
>
> These are roughly our conclusions from discussing this patch series
> with Tomasz F.

Ok. Thanks for your comments. I will redo this patch series and post them.

Thanks,
Thomas.

>
> --
> Thanks,
> Sylwester