Re: [RFC PATCH 2/3] clk: adjust clocks to their requested rate after parent changes

Elaine Zhang
2016-07-06T01:41:18Z

On 07/06/2016 06:24 AM, Heiko Stuebner wrote:
> Hi Elaine,
>
> Am Dienstag, 5. Juli 2016, 15:27:30 schrieb Elaine Zhang:
>> On 05/03/2016 12:36 AM, Heiko Stuebner wrote:
>>> Given a hirarchy of clk1 -> [div] -> clk2, when the rate of clk1 gets
>>> changed, clk2 changes as well as the divider stays the same. There may
>>> be cases where a user of clk2 needs it at a specific rate, so clk2
>>> needs to be readjusted for the changed rate of clk1.
>>>
>>> So if a rate was requested for the clock, and its rate changed during
>>> the underlying rate-change, with this change the clock framework now
>>> tries to readjust the rate back to/near the requested one.
>>>
>>> The whole process is protected by a new clock-flag to not force this
>>> behaviour change onto every clock defined in the ccf.
>>>
>>> Signed-off-by: Heiko Stuebner <heiko@sntech.de>
>>> ---
>>>
>>> drivers/clk/clk.c | 13 +++++++++++--
>>> include/linux/clk-provider.h | 1 +
>>> 2 files changed, 12 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
>>> index 65e0aad..22be369 100644
>>> --- a/drivers/clk/clk.c
>>> +++ b/drivers/clk/clk.c
>>> @@ -1410,6 +1410,9 @@ static struct clk_core
>>> *clk_propagate_rate_change(struct clk_core *core,>
>>> return fail_clk;
>>>
>>> }
>>>
>>> +static int clk_core_set_rate_nolock(struct clk_core *core,
>>> + unsigned long req_rate);
>>> +
>>>
>>> /*
>>>
>>> * walk down a subtree and set the new rates notifying the rate
>>> * change on the way
>>>
>>> @@ -1494,6 +1497,12 @@ static void clk_change_rate(struct clk_core
>>> *core)
>>>
>>> /* handle the new child who might not be in core->children yet */
>>> if (core->new_child)
>>>
>>> clk_change_rate(core->new_child);
>>>
>>> +
>>> + /* handle a changed clock that needs to readjust its rate */
>>> + if (core->flags & CLK_KEEP_REQ_RATE && core->req_rate
>>> + && core->new_rate != old_rate
>>> + && core->new_rate != core-
>> req_rate)
>>> + clk_core_set_rate_nolock(core, core->req_rate);
>>>
>>> }
>>
>> I tests found a problem, about set the freq order.
>> e.p:
>> [VPLL]
>>
>> ------ [div] ----- dclk_vop
>> If I change VPLL freq 148.5M to 594M, dclk_vop freq will changed as:
>> 148.5M->24M->594M->1485.5M.
>> But we not hope the dclk_vop have a high freq,it will make the system
>> crash or make vop not work well.
>>
>> So if the VPLL is improve the freq, we need to set dclk_vop div first,
>> and than set VPLL freq.
>> If VPLL is reduce the freq, we need to set vpll first,and set dclk_vop
>> div.
>>
>> This is just a example,for all change parent freq, we need follow this
>> operation.
>> Do you have a better idea for this problem?
>
> In general it seems my simplicistic approach only really works for really
> simple clock-setups and thus is likely not really usable for general things.
>
> For the VPLL on the rk3399 we were discussion a different approach in [0],
> as VPLL usage (aka which vop gets to control it) is likely to complicated to
> have this done in the clock-framework-
>
> Doug wanted to take a look and add some thoughts and I guess he'll just do
> that after the 4th of july celebrations.
>
OK, Regardless of the VPLL and vop.
The current software of clock, there are some problems.
e.p:
[GPLL]
------ [div] ----- aclk_perilp
If I set GPLL 1200M use "assigned-clock-rate".My be the default div of
aclk_perilp is 2, GPLL default freq is 600M.
If I set GPLL first,the aclk_perilp freq will changed as
300M->600M->300M.But aclk_perilp 600M is a unsafety.It will make the
system crash.
Aclk_perilp is sizeoff at 300M.It not allowed over frequency.

So if I init the PLL freq use "assigned-clock-rate", I need to list it's
child clk, make sure it's child clk div is enough,make sure the child
clk freq is below the sizeoff freq.

Do you have a better idea for this problem?
>
> Heiko
>
>
> [0] http://lists.infradead.org/pipermail/linux-rockchip/2016-June/010400.html
>
>
>
>