lkml.org 
[lkml]   [2015]   [May]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 6/9] clk: pistachio: Propagate rate changes in the MIPS PLL clock sub-tree
From
On Fri, May 22, 2015 at 10:52 AM, Ezequiel Garcia
<ezequiel.garcia@imgtec.com> wrote:
>
>
> On 05/22/2015 02:42 PM, Andrew Bresticker wrote:
>> On Thu, May 21, 2015 at 4:57 PM, Ezequiel Garcia
>> <ezequiel.garcia@imgtec.com> wrote:
>>> This commit passes CLK_SET_RATE_PARENT to the "mips_div",
>>> "mips_internal_div", and "mips_pll_mux" clocks. This flag is needed for the
>>> "mips" clock to propagate rate changes up to the "mips_pll" root clock.
>>>
>>> Signed-off-by: Govindraj Raja <Govindraj.Raja@imgtec.com>
>>> Signed-off-by: Ezequiel Garcia <ezequiel.garcia@imgtec.com>
>>
>> IIRC the clk core will prefer changing a downstream divider over
>> propagating the rate change up another level. So, for example, if
>> MIPS_PLL is initially 400Mhz and we request a MIPS rate of 200Mhz,
>> we'll change the first intermediate divider to /2 rather than
>> propagate the rate change up to MIPS_PLL. Wouldn't it be more
>> power-efficient to set the MIPS_PLL directly to the requested rate
>> rather than using external dividers to divide it down?
>>
>
> Indeed.
>
> Do you think we still want to be able to change the MIPS clk rate and
> propagate the change up to the PLL? Otherwise, I'll drop this patch and
> I'll drop the DIV_F and MUX_F macro patches.

Well I do think we want to propagate changes from MIPS up to MIPS_PLL,
but we need to work around the behavior of CLK_SET_RATE_PARENT when
applied to divider clocks. Since there's no reason to ever set the
dividers between MIPS and MIPS_PLL to something besides /1
(James/Govindraj/Damien, correct me if I'm wrong here), then I think
we could just set CLK_DIVIDER_READ_ONLY on those dividers. It's a bit
of a hack, but it's certainly simpler than writing a separate CPU
clock driver.


\
 
 \ /
  Last update: 2015-05-22 20:41    [W:0.038 / U:0.580 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site