Re: [PATCH v2 04/10] arm64: dts: imx8mn: Add access-controller references

[Peng Fan <peng.fan@oss.nxp.com>]

On Mon, Feb 10, 2025 at 04:48:56PM +0100, Alexander Stein wrote:
>Am Montag, 10. Februar 2025, 03:36:48 CET schrieb Peng Fan:
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>> > Subject: Re: [PATCH v2 04/10] arm64: dts: imx8mn: Add access-
>> > controller references
>> > 
>> > Hi Peng,
>> > 
>> > Am Freitag, 7. Februar 2025, 13:02:13 CET schrieb Peng Fan:
>> > > On Fri, Feb 07, 2025 at 09:36:09AM +0100, Alexander Stein wrote:
>> > > >Mark ocotp as a access-controller and add references on peripherals
>> > > >which can be disabled (fused).
>> > >
>> > > I am not sure whether gpcv2 changes should be included in this
>> > > patchset or not. Just add access-controller for fused IP will not work.
>> > 
>> > Well, I was able to successfully boot a i.MX8M Nano DualLite.
>> > 
>> > > i.MX8M BLK-CTRL/GPC will hang if the related power domain is still
>> > > touched by kernel. The pgc can't power up/down because clock is
>> > gated.
>> > 
>> > Well, with GPU node disabled, no one should enable the power domain.
>> > But to be on the safe side I would also add access-controllers to the
>> > corresponding power domains as well.
>> > 
>> > > This comment also apply to i.MX8MM/P.
>> > 
>> > Sure. Do you have any information what is actually disabled by those
>> > fused?
>> > It seems it's the IP and their power domains. Anything else?
>> 
>> In NXP downstream there is a patch for  drivers/pmdomain/imx/imx8m-blk-ctrl.c
>> 
>> soc: imx8m-blk-ctrl: Support fused modules
>>     
>>     For fused module, its pgc can't power up/down and clock is gated.
>>     Because imx8m-blk-ctrl driver will pm_runtime_get_sync/pm_runtime_put
>>     all power domains during suspend/resume. So we have to remove the
>>     pgc and clock of fused module from blk-ctrl DTS node.
>>     Update the driver to support such case.
>> 
>> But this patch also needs U-Boot to update device tree nodes,
>> I recalled that U-Boot will remove gpc nodes, but not update blk-ctrl nodes.
>
>Does it work, if we add the access-controller as well for pgc_gpu3d
>on imx8mp? There is nothing in blk-ctrl AFAICS. But for VPU there is.

Adding access-controller under pgc_gpu node will not make fwdevlink
work for the pgc_gpu nodes. It does not have compatible, and device
is created by gpcv2 driver using platform_device_alloc. Same to vpu.

>Which clock needs to be removed there in case g1 is disabled?

Take i.MX8MP VC8000E as example, the vpumix blk ctrl, the vc8000e
reference under vpumix blkctrl should be removed, including pd and clock.

So for non-blkctrl nodes, it is fine to use access-controller and rely
on fwdelink to defer probe. But for blk ctrl nodes, it will not work.

For pgc nodes, it may or may not matter, not very sure for now.

For blk ctrl nodes, we need provide a generic API saying
access_control_check or directly using nvmem API.

Regards,
Peng

>
>Best regards,
>Alexander
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