Re: [PATCH v4 00/13] ARM: dts: imx6ul: Add Variscite VAR-SOM-6UL and DART-6UL

[Stefano Radaelli <stefano.radaelli21@gmail.com>]

On Thu, Oct 01, 2026 at 02:43:44PM -0400, Hugo Villeneuve wrote:

Hi Hugo,

> 
> Great to know Variscite is adding support for the DART-6UL.
> 

Thank you Hugo :)
Over the past year, we have been prioritizing security and consistency
by adopting a mainline-first approach.
We have added support for almost all of our SOMs and configurations,
as well as several driver changes and additions:
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/log/?h=master&qt=author&q=Stefano+Radaelli
And now it's time for the immortal i.MX6UL!

> 
> Please work with the existing modular DTSI files, do not simply remove
> them and reimplement them into your own files.
> 

Agreed. Where possible, I’ll reuse the modular files you added and
propose fix commits wherever changes are needed.

> 
> I tested it and it works. But like I said, if adjustments need to be
> made, they are welcome and can be done in a separate patch to fix it.
> This sequencing is something not very well documented in Variscite
> datasheets. I asked Variscite support to improve the documentation for
> that aspect but it was not accepted.
> 
> 
> > For the LWB5 option, the procedure enables WIFI_PWR, waits 10 ms,
> > enables WLAN_EN and BT_EN, waits 200 ms, then lowers BT_EN before
> > re-enumerating the SDIO device.
> > The other Broadcom option does not use the separate WIFI_PWR step.
> > The existing regulator and MMC power-sequence nodes do not express that
> > complete, module-dependent procedure, particularly the BT_EN step during
> > Wi-Fi initialization.
> > The scripts also select the Bluetooth firmware according to the detected
> > SDIO device.
> 
> Firmware loading is handled properly by the kernel without external
> scripts (tested with Concerto EVK).
> 
> 
> > We use that procedure to avoid sequencing-related failures for our
> > customers.
> > This approach is not new to Variscite’s mainline DTS files.
> 
> Yes, this is an old way of doing things, which may have been
> appropriate in the past when proper support in the kernel was missing
> to achieve the proper sequencing, but no longer true these days, unless
> I am mistaken.
> 

We are glad the kernel-managed sequence works on your Concerto EVK.
However, it is wrong for the LWB5 module configuration we support:
it does not follow the required power-up order and timing validated
by Variscite.
The sequence is based on the module requirements and has been tested
in our labs and across customer configurations over many years.
A successful test on your EVK does not show that it is correct for all
the modules and configurations we ship.

The GPL-2.0-only userspace scripts implement this required sequence.
This is not a matter of preference or an old approach we kept by habit;
replacing it with the sequence in the current DTS would risk breaking
supported Variscite configurations.
If a future kernel implementation can reproduce the complete,
module-specific sequence, Variscite will be happy to update all affected
DTS files to use it, after completing the necessary lab testing across
the supported module variants and configurations.

If you need any additional material, datasheets, or other information
from Variscite, please let me know at stefano.r@variscite.com.
I’ll be happy to provide whatever is needed!

Best Regards,
Stefano