[RFC PATCH 0/2 v1] Propagate bootph* property to all parent nodes

[Quentin Schulz]

Hi Moteen,

On 2/26/25 6:57 AM, Moteen Shah wrote:
> 
> On 17/02/25 20:32, Quentin Schulz wrote:
>> Hi Moteen,
>>
>> On 2/12/25 10:18 AM, Moteen Shah wrote:
>>> [You don't often get email from m-shah at ti.com. Learn why this is 
>>> important at https://aka.ms/LearnAboutSenderIdentification ]
>>>
>>> In the U-Boot pre-relocation stage, if the parent node lacks bootph*
>>> property and the driver lacks a pre-reloc flag, all of its subsequent
>>> subnodes gets skipped over from driver binding—even if they have a
>>> bootph* property.
>>>
>>> This series addresses the issue by scanning through all the subnodes
>>> of the current node for the bootph* property and propagate it to all
>>> of its supernodes, ensuring that all of the applicable drivers are
>>> bound and probed prior to relocation. This series implements one of
>>> the solutions mentioned in [0].
>>>
>>> Since, all the nodes which are not having any bootph* property will
>>> also be traversed, we will have to incur some overheads in boot time,
>>> hence protecting the feature under a config.
>>>
>>> Boot time overheads:
>>>      Baseline: Upstream u-boot
>>>
>>>      Patch test: Baseline + remove all bootph-all properties from
>>>      *-u-boot.dtsi except the ones which are supposed to be probed
>>>      but have no bootph in any of its subnode.
>>>
>>>      J7200 delta from baseline  : ~100ms
>>>      J784S4 delta from baseline : ~350ms
>>>
>>
>> Pfew, that's a lot of time. Can you tell us what's the delta in 
>> percentage from baseline? Because if your system is usually booting in 
>> one minute, 100ms isn't too bad :)
>>
> 
> Our system's boot time is about 2.2s (J7200) and that of J784s4 is 2.7s 
> (owing to a larger DT).
> 

OK so respectively 4.5 and 12.9% boot time increase if I'm doing maths 
the right way, that's really a lot :/

> 
>> FYI, I believe we've been hit by this issue on Rockchip but cannot 
>> find the thread or patch right now.
>>
>> For TPL and SPL, the Device Tree is parsed and looked for appropriate 
>> bootph properties. Any node which doesn't have a bootph property and 
>> doesn't have any children with a bootph property is removed from the 
>> tree. However, the bootph property (if only present in a children 
>> node) isn't propagated (meaning the node doesn't get the property). 
>> This is done by fdtgrep.
>>
>> The issue is that for U-Boot proper pre-relocation, the whole DT is 
>> taken and only nodes with the appropriate bootph property is probed 
>> and children nodes do NOT count as opposed to the TPL/SPL case.
>>
>> My idea was that maybe we should rather propagate the property, at the 
>> very least in U-Boot proper pre-relocation. This does mean we will 
>> increase (by which amount?) the size of the DT in U-Boot proper 
>> because we would add this property recursively up the tree from a node 
>> that has the bootph property for U-Boot proper pre-relocation. This 
>> **could** be an issue as the DT could be passed between stages and we 
>> would then hit the size limit. Sadly, I didn't take the time to look 
>> into adding support for that in fdtgrep nor will I have the time to do 
>> it, so take this as me sharing my wish list with you.
>>
> 
> Thanks for sharing this, the size increase this patch introduces for 48 
> such bootph-* tags is about 1.5KB's, we can go ahead and bind the super 
> parent to bypass the part of adding the tag, but for the next parent we 
> will have to traverse again down the DT adding in unnecessary 
> traversals(considering a case that we are 4-5 levels deep in the DT).
> 

j784s4-evm/u-boot.dtb is 131616B
j7200-evm/u-boot.dtb is 88368B

so 1.5KiB would mean respectively, 1.1 and 1.7% in **DTB** **size** 
increase, not sure how that translate in terms of boot time though.

Reading Tom's notes from the meeting a few days ago where this was 
seemingly discussed, I believe the issue is that the kernel wants the 
bootph- property only in the child node. But I assume this applies only 
to the DTS, which would be fine with this build time propagation of the 
bootph- properties to node parents recursively. Would the kernel also 
want the same limitation for the DTB?

Cheers,
Quentin