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SubjectRe: [PATCH V1 1/4] qcom: spmi-wled: Add support for qcom wled driver
On 2017-11-17 12:26, Bjorn Andersson wrote:
> On Thu 16 Nov 22:36 PST 2017, kgunda@codeaurora.org wrote:
>
>> On 2017-11-16 22:25, Bjorn Andersson wrote:
>> > On Thu 16 Nov 04:18 PST 2017, Kiran Gunda wrote:
>> >
>> > > WLED driver provides the interface to the display driver to
>> > > adjust the brightness of the display backlight.
>> > >
>> >
>> > Hi Kiran,
>> >
>> > This driver has a lot in common with the already upstream pm8941-wled.c,
>> > because it's just a new revision of the same block.
>> >
>> > Please extend the existing driver rather than providing a new one
>> > (and yes, renaming the file is okay).
>> >
>> > Regards,
>> > Bjorn
>>
>> Hi Bjorn,
>>
>> Yes this driver design is similar to pm8941, however the WLED HW block
>> has undergone quite a few changes in analog and digital from PM8941 to
>> PM8998.
>
> I can see that, looking at the documentation.
>
>> Few of them include splitting one module into wled-ctrl and wled-sink
>> peripherals, changes in the register offsets and the bit
>> interpretation.
>
> This is typical and something we need to handle in all these drivers,
> to
> avoid having one driver per platform.
>
>> Hence we concluded that it was better to have a new driver to support
>> this new gen WELD module and decouple it from the pm8941.
>
> Okay, I can see how it's easier to not have to case about anything but
> pmi8998 in this driver, but where do you add the support for other WLED
> versions? What about PMI8994? Will there not be similar differences
> (registers that has moved around) in the future?
>
>> Also, going forward this driver will support AMOLED AVDD rail (not
>> supported by pm8941) touching a few more registers/configuration and
>> newer PMICs.
>
> Is this a feature that was introduced in PMI8998? Will this support not
> be dependent on the pmic version?
>
>> So spinning off a new driver would make it cleaner and easier to
>> extend further.
>>
>
> It's for sure easier at this point in time, but your argumentation
> implies that PMI8998+1 should go into it's own driver as well.
>
> I suspect that if you're going to reuse this driver for future PMIC
> versions you will have to deal with register layout differences and new
> feature set, and as such I'm not convinced that a new driver is needed.
>
>
> Can you give any concrete examples of where it is not possible or
> undesirable to maintain the pm8941 support in the same driver?
>
> Regards,
> Bjorn

Hi Bjorn,

Thanks for the inputs! Following are the reasons to go for the new
driver
and this driver can support 5 PMICs.

1.Majority of register, offsets and config values don’t match up
between
PMI8998 and PM8941
2.Feature such as – SC protection handling in SW cannot be done for 8941
as
there is no SC event/irq, AMOELD AVDD cannot supported by PM8941
3.Feature such as – string auto-calibration even if common will have to
use
different offsets/registers in the same SW logic
4.PMI8998, PMI8994, PMI8950 and PM660 all of them have this same WLED
module
(and register map) with very minor changes unlike 8941.

Thanks,
Kiran


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