[PATCHv3 2/8] devfreq: exynos: Add documentation for generic exynos memory bus frequency driver

[Chanwoo Choi]

Hi Viresh,

I explained the relation between memory bus group and memory bus block on following patch[1].
- [1] https://lkml.org/lkml/2015/1/8/642

On 01/20/2015 04:19 PM, Viresh Kumar wrote:
> On 9 January 2015 at 02:48, Rob Herring <robherring2 at gmail.com> wrote:
>> Adding Viresh.
> 
> Sorry for being too late, I was very busy with other cpufreq stuff I was doing
> and saved this thread for later as it required me to understand it properly..
> 
>>> +Required properties for memory bus block:
>>> +- clock-names : the name of clock used by the memory bus, "memory-bus".
>>> +- clocks : phandles for clock specified in "clock-names" property.
>>> +- #clock-cells: should be 1.
>>> +- frequency: the frequency table to support DVFS feature.
>>
>> So you have just defined a new OPP table format. We already have one
>> and Viresh is working to create a more extendable one. He asked about
>> what's needed in devfreq, so Viresh here you go. :)
> 
> I failed to understand what's new here, probably I need more clarity on
> what we are doing here..
> 
> So, this is what I see from OPPs point of view, everything else stripped out.
> 
>>> +       memory_bus_int: memory_bus at 1 {
> 
>>> +               operating-points = <
>>> +                       400000 950000
>>> +                       200000 950000
>>> +                       133000 925000
>>> +                       100000 850000
>>> +                       80000  850000
>>> +                       50000  850000>;
> 
> So these are the OPPs your "groups" support and below ones are
> the frequencies that each block will support. Right ?

Right.
But, the frequency of OPPs is only used for devfreq ondemand governor.
After deciding the proper frequency of memory bus on ondemand governor,
exynos-bus.c (exynos memory bus frequency driver) use the frequency table
of memory bus blocks on below to change the clock rate of memory bus block.

> 
>>> +               blocks {
> 
>>> +                               frequency = <
>>> +                                       100000
>>> +                                       100000
>>> +                                       100000
>>> +                                       100000
> 
> Why this replication here ?

Firs of all,
I explain the hierarchy of Exynos memory buses.

For example of Exynos3250 memory bus,
This patch divide the memory bus group according to power rail (regulator).
- MIF (Memory Interface ) memory bus group uses the VDD_MIF regulator.
- INT (Internal) memory bus group uses the VDD_INT regulator.

Each memory bus group contains only one power rail(regulator) and one more memory bus blocks as follwing:

- MIF memory bus group                     
power rail(VDD_MIF)-->|--- memory bus for DMC (Dynamic Memory Controller) block (dmc clock)

- INT memory bus group
                      |--- memory bus for PERI block (aclk_100 clock)
                      |
                      |--- memory bus for DISPLAY block (aclk_160 clock)
                      |  
                      |--- memory bus for ISP block (aclk_200 clock)
                      |
                      |--- memory bus for GPS block (aclk_266 clock)
power rail(VDD_INT)-->|
                      |--- memory bus for MCUISP block (aclk_400_mcuisp clock)
                      |
                      |--- memory bus for Leftbus block (gdl clock)
                      |
                      |--- memory bus for Rightbus block (gdr clock)
                      |
                      |--- memory bus for MFC block (mfc clock)


Exynos3250 has following table for INT memory bus group:
All clocks of INT memory bus group have to contain the same entry count
againt the number of 'virtual freqw'. So, each memory bus clock could have duplicate clocks.

------------------------------------------------------------------------
Level|virtual freq|PERI's clk|Display's clk|ISP's clk|GPS's clk| voltage|
------------------------------------------------------------------------
L6   |400000      |100000    |200000       |200000   |300000   | 95000  |
L5   |200000      |100000    |160000       |200000   |200000   | 95000  |
L4   |133000      |100000    |100000       |100000   |133000   | 92500  |
L3   |100000      |100000    |80000        |80000    |100000   | 85000  |
L2   |80000       |50000     |80000        |50000    |50000    | 85000  |
L1   |50000       |50000     |50000        |50000    |50000    | 85000  |
-------------------------------------------------------------------------
(Except for mcuisp, leftbus, rightbus, mfc block)

This table is used for devfreq ondemand governor as following:
1. ondemand governor in devfreq use the 'virtual freq' to devcide the proper
   frequency for memory bus. 
2. ondemand governor executes the *_target() function to set clock rate and voltage.
3. *_target() function in exynos-bus.c changes the clock rate of {PERIS|Display|ISP|GPS} clk
   according to decided 'Level' by devfreq ondemand governor.

> 
>>> +                                       50000
>>> +                                       50000>;
>>> +                       };
> 
> How are the above two tables (operating-points and frequency) related
> here? What about the voltages at which these frequencies are possible ?

I explained it on the upper.

> 
>>> +                       display_block: memory_bus_block2 {
> 
>>> +                               frequency = <
>>> +                                       200000
>>> +                                       160000
>>> +                                       100000
>>> +                                       80000
>>> +                                       80000
>>> +                                       50000>;
>>> +                       };
> 
>>> +                       isp_block: memory_bus_block3 {
> 
>>> +                               frequency = <
>>> +                                       200000
>>> +                                       200000
>>> +                                       100000
>>> +                                       80000
>>> +                                       50000
>>> +                                       50000>;
>>> +                       };
> 
>>> +                       gps_block: memory_bus_block4 {
> 
>>> +                               frequency = <
>>> +                                       300000
>>> +                                       200000
>>> +                                       133000
>>> +                                       100000
>>> +                                       50000
>>> +                                       50000>;
>>> +                       };
> 
> same for others as well..

I explained it on the upper.

Best Regards,
Chanwoo Choi