Re: [PATCH v2 1/7] soc: rockchip: add driver for rockchip io domains

[Michael Riesch <michael.riesch@wolfvision.net>]

Hi Sascha,

On 9/21/22 11:46, Sascha Hauer wrote:
> On Mon, Sep 19, 2022 at 01:39:42PM +0200, Michael Riesch wrote:
>> The IO domains in Rockchip SoCs need to be configured to match the
>> corresponding bank voltage. In Linux this is achieved by means of a
>> platform driver that reads the voltage value of the supplies and
>> configures the bits in the general register file (GRF) accordingly.
>> Port this driver to barebox to provide support for the Rockchip
>> RK356x SoCs.
>>
>> Signed-off-by: Michael Riesch <michael.riesch@wolfvision.net>
>> ---
>>  drivers/soc/Kconfig              |   1 +
>>  drivers/soc/Makefile             |   1 +
>>  drivers/soc/rockchip/Kconfig     |  17 +++
>>  drivers/soc/rockchip/Makefile    |   6 +
>>  drivers/soc/rockchip/io-domain.c | 223 +++++++++++++++++++++++++++++++
>>  5 files changed, 248 insertions(+)
>>  create mode 100644 drivers/soc/rockchip/Kconfig
>>  create mode 100644 drivers/soc/rockchip/Makefile
>>  create mode 100644 drivers/soc/rockchip/io-domain.c
> 
> There's nothing in this driver that makes sure it is probed before the
> users of the io domains. What happens when the users are probed before
> the io domain driver?

Correct. Unfortunately, the situation is quite the same in the kernel.
Only recently there was a discussion as to how to resolve this issue
[0]. While the RFC in [0] was received well there is no mainline
solution to this problem. I would suggest that the mainline kernel
solution is adopted once there is one.

In the mean time we could
 - accept that it just works for some reason (TM)
 - leave the magic bits in the low-level initialization to be on the
   safe side
 - simply wait
 - ???

> Normally I would expect that the consumers have some phandle to their io
> domain, but there's nothing like it in the device trees.

The RFC in [0] suggests that the pinctrl is a consumer of the io
domains, which would be in alignment with your expectations.

Best regards,
Michael

[0]
https://lore.kernel.org/lkml/20220802095252.2486591-1-foss+kernel@0leil.net/T/