Re: [PATCH RFT 2/3] media: i2c: dw9719: Add DW9800W support

[Danila Tikhonov <danila@mainlining.org>]

Hi Griffin, Sakari,

Thank you for the clarification.

On 07/08/2026 17:30, Griffin Kroah-Hartman wrote:
> Hello Sakari, Danilla,
>
> On 05/08/2026 13:29, Sakari Ailus wrote:
>> Hi Danila, Griffin,
>>
>> On Tue, Aug 04, 2026 at 09:27:01PM +0300, Danila Tikhonov wrote:
>>> Hi Sakari,
>>>
>>> Thank you for your comment.
>>>
>>> On 04/08/2026 11:40, Sakari Ailus wrote:
>>>> Hi Danila,
>>>>
>>>> Thank you for the patch.
>>>>
>>>> On Sat, Aug 01, 2026 at 09:04:15PM +0300, Danila Tikhonov wrote:
>>>>> The DW9800W uses the same chip ID and register layout as the DW9800K,
>>>>> but requires different default VCM frequency value.
>>>> Is this a real difference between the two models or what fits for the
>>>> attached lens? Too bad the datasheet isn't publicly available. :-(
>>>>
>>>> At least the differing default and constraints for 
>>>> dongwoon,vcm-prescale
>>>> needs to be documented in bindings.
>>> I share your skepticism and have essentially the same concerns. Since I
>>> do not have the DW9800K datasheet, I cannot say with certainty how it
>>> differs from the DW9800W.
>> Indeed. The limits should have been added for dw9800k, too, but I 
>> guess I
>> missed this in review. :-\
>>
>>> In particular, the parameter referred to as the VCM frequency in the
>>> driver is used to derive the SACT value. For the DW9800W, SACT[5:0]
>>> defines the actuator resonance period in SAC mode and the one-step
>>> period in LSC mode. The datasheet gives the corresponding formulas as:
>>> - tVIB = 6.3 ms + SACT * 0.1 ms
>>> - LSC 1-step period = 252 µs + SACT * 4 µs
>>>
>>> Therefore, the default value may differ between the DW9800K and DW9800W
>>> if the formulas or timing characteristics used to calculate SACT are
>>> different.
>> Griffin, would you be able to comment this?
>
> After checking on my side, DW9800W and K are almost identical in both 
> structure
> and register values, including how tVIB and tLSC are calculated, 
> DW9800K has an extra
> register that can change the output current to 130mA but we don't ever 
> use that.
>
> We didn't have a datasheet when working on the DW9800k so we had to go 
> off of
> the downstream driver during runtime to get our register values. The 
> datasheet is a
> much more reliable source to be using for this instead.
>
> My colleague has already identified ways to fix the bindings, which we 
> will
> tackle ourselves.
>
I'm glad you were able to clarify the situation, as this should help us
handle both IC variants correctly.
>> Another matter: the comment on dw9800k says there's no device ID. So is
>> there a device ID that wasn't just checked earlier or is there really no
>> device ID?
>
> Indeed, it turns out the DW9800K DOES have an info register, which 
> should be
> 0xEB, that's on us for not updating it after we received more 
> documentation.
>
Given this, and assuming everyone agrees, I think it would make sense
for me to leave the DW9800K untouched in the next version of this patch
series. Since it turns out that the DW9800K has a different Chip ID, you
can fix the Chip ID check for it separately based on the information you
have.

One point is still unclear to me, though: is the default VCM frequency
the same for both ICs, or does it differ between them?

> Thanks for drawing our attention to this! Nice patch.
>
> Griffin
>
---
Best regards,
Danila