[RFC PATCH] arm64: defconfig: Set MFD_TPS6594_I2C as built-in

[Nishanth Menon]

On 23:01-20240819, Krzysztof Kozlowski wrote:
> On 19/08/2024 22:43, Judith Mendez wrote:
> > SK-AM62A-LP is a device targeting automotive front-camera applications
> > among other use-cases. It utilizes the TPS6593x PMIC (interfaced over I2C)
> > to power the SoC and various other peripherals on the board [1].
> > 
> > MMCSD requires the PMIC to be setup correctly before setting the bus
> > pins to 1.8V using the TPS6594 driver interfaced over i2c.
> > 
> > Currently, the following could be seen when booting the am62ax platform:
> > 
> > "platform fa00000.mmc: deferred probe pending: platform: supplier regulator-5 not ready"
> > "vdd_mmc1: disabling"
> > 
> > and a failure to boot the SK-AM62A-LP.
> > 
> > One solution is to use initramfs [2], but using initramfs increases the
> > boot time for this automotive solution which requires faster boot time
> > parameters.
> 
> This is a defconfig, not a distro/product config, so your product
> constraints are not really relevant. You are supposed to boot defconfig
> with proper initramfs with necessary modules.
> 
> I don't get why people mistake defconfig with their product stuff...
> 
> > 
> > Another solution is to change MFD_TPS6594_I2C to built-in, that way the
> > PMIC is setup and the regulators are ready before MMCSD switches to UHS
> > mode, this is the preferred solution since it does not increase boot time
> > like the initramfs solution does.
> 
> Use initramfs. Several devices, e.g. most Android ones, have fixed size
> of boot partition, so size of kernel is important.

am62a products do not use android in general. Standard distros such
as debian etc usage are limited as well. These products tend to have
limited resources just sufficient for the normal operations.

While I understand that we do keep the product usage model separate
from what upstream defconfig looks like, we have been very careful
to only enable the basic configurations necessary for default system
startup. During the initial days of K3, we had considered going down
the initramfs route, but realized that this was not a practical
option for developers to sustain and iterate quickly for triage or
development. Till date, we have maintained nfs and sd card boot as
default to allow for automated testing of upstream kernel.

I understand that you have provided similar comments for other
platforms[1] as well, but, I am now wondering if this is a new rule
we are taking in aarch64 platforms to allow just initramfs and
force all drivers to be modules (I understand that is the default
preference in android, but that is not true in other ecosystems). I am
curious if this was some sort of conclusion in the list (my search of
public-inbox seems to fail me here).

[1] https://lore.kernel.org/linux-arm-kernel/e08e6325-4b2b-c1ce-b33a-877de2c0babe@linaro.org/
-- 
Regards,
Nishanth Menon
Key (0xDDB5849D1736249D) / Fingerprint: F8A2 8693 54EB 8232 17A3  1A34 DDB5 849D 1736 249D