Re: [PATCH v2 0/2] Add xo calibration support for wifi rf clock

[Sven Eckelmann <sven@narfation.org>]

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On Wednesday, 20 March 2019 05:45:09 CET Govind Singh wrote:
> PMIC XO is the clock source for wifi rf clock in integrated wifi
> chipset ex: WCN3990. Due to board layout errors XO frequency drifts
> can cause wifi rf clock inaccuracy.
> XO calibration test tree in Factory Test Mode is used to find the
> best frequency offset(for example +/-2KHz )by programming XO trim
> register. This ensure system clock stays within required 20 ppm
> WLAN rf clock.
> 
> Retrieve the xo trim offset via system firmware (e.g., device tree),
> especially in the case where the device doesn't have a useful EEPROM
> on which to store the calibrated XO offset (e.g., for integrated Wifi).
> Calibrated XO offset is sent to fw, which compensate the clock drift
> by programing the XO trim register.

Who is responsible to fill in this values in the device-tree? On other 
products, the correct XTAL capacitor registers values are calibrated on 
different devices (in the same product line) separately to ensure that each 
device has a minimal inaccuracy. During the boot of the device, the two u8 
taken from params_for_tuning_caps (inside the EEPROM) are just written to the 
AR_CH0_XTAL register (mapped to the correct the INDAC and OUTDAC region).

Your patch here seems to be doing something similar (you may correct me if I 
misinterpret something) but you are already saying that these devices don't 
have an EEPROM. This is already quite odd because then we also wouldn't have 
temperature compensation (also stored in per device EEPROM/precal data for 
other devices).

So you move it to the device tree. By default, this device tree is most likely 
a static thing which is shipped with the rest of the firmware. So no per 
device data is stored in this DTB on the flash. To include device specific 
information (mac addresses, calibration data, ...), you could also have the 
bootloader (u-boot for example) change the device tree during the boot process 
and let it inject the device specific XO trim register data.

How is this planned to work? Is the bootloader expected to modify the device 
tree during the boot to provide the device specific xo-cal-data. If yes, where 
is it getting the information from? And is there already support for QDART for 
it?

If you do this, why aren't you using the data from qcom,ath10k-pre-
calibration-data. At least for other ath10k devices, it includes the 
previously mentioned tuning caps. It is the first time I heard about an XO 
trim register and thus it might be something different than what I expect.


Last question: why is it an u32 when the message with xo_cal_data can only 
transport an u8?

Kind regards,
	Sven

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