Re: [PATCH v2 2/2] leds: add Qualcomm PM8941 WLED driver

[Bjorn Andersson <bjorn@kryo.se>]

On Tue, Feb 17, 2015 at 6:45 PM, Stephen Boyd <sboyd@codeaurora.org> wrote:
> On 02/17/15 15:02, Bjorn Andersson wrote:
>> On Thu, Feb 12, 2015 at 8:26 PM, Stephen Boyd <sboyd@codeaurora.org> wrote:
[..]
>>> This doesn't seem to do anything for the OVP spike mentioned in this
>>> patch[1]. Do you see that problem on your device? I imagine the PMIC is
>>> the same.
>>>
>>> [1]
>>> https://www.codeaurora.org/cgit/quic/la/kernel/msm/commit/?id=fef9e15072562f0f28dc7066dcdd69388df81ed3
>>>
>> That's odd, I can't find that fix in any officially supported releases
>> for 8974 - which Courtney used as reference for this driver.
>>
>> Just to make sure I understand the solution; when disabling the sinks
>> the over-voltage-protection sometimes triggers, so we should detect
>> that and reset the ovp configuration?
>>
>> I presume the side effect would be that the sinks would not give any
>> output until this is done?
>>
>
> It seems that commit is not very good at describing the problem. From
> what I can tell, the inductor current may spike when the WLED is turned
> off and the switch is stuck on (the circuit is a boost convertor). To
> make sure this doesn't happen, we force an OVP so that the switch is
> known to be open (i.e. off) and thus can't cause the current spike when
> we disable.
>

Apparently that commit is only half of the solution, there's another
commit earlier in history with the same commit message [2].

With both [1] and [2] in place there are a bunch of different
operations going on, so I'm not able to fully map these to your
description - which does make sense.

[2] https://www.codeaurora.org/cgit/quic/la/kernel/msm/commit/?id=b1a2f61113c69d2aba68c583101ac40a05cb2c5b

Regards,
Bjorn