Messages in this thread | | | Date | Mon, 26 Jun 2023 09:39:31 +0200 | From | Stephan Gerhold <> | Subject | Re: [PATCH v2 2/2] arm64: dts: qcom: msm8939-samsung-a7: Add initial dts |
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On Mon, Jun 26, 2023 at 01:05:22AM +0100, Bryan O'Donoghue wrote: > On 25/06/2023 20:43, Stephan Gerhold wrote: > > Is it really worth it to support a half-working bootloader though? > > > No one will ever be able to use this properly without fixing the > > bootloader. SMP doesn't work with the stock bootloader, many devices > > need display panel selection in the bootloader and on some Samsung > > devices there is not even USB and UART without special fixes in the > > bootloader. > > Why set the bar higher than necessary to boot a kernel though ? > > Its two lines in a dts. >
I see your point but after adding some really weird workarounds for various devices in lk2nd I can't help seeing it more complicated.
Adding "just two lines in a dts" is the general case, but I can also give plenty other examples where one has to:
- Duplicate the entire downstream MDSS/MDP/display DT nodes because the bootloader uses them to initialize the display (older Sony MSM8974 devices) [1]
- Add random DT nodes because the stock bootloader insists on updating random DT properties in them [2]
- Use a custom bootloader anyway to boot 64-bit Linux, because the stock bootloader doesn't implement the 32-bit -> 64-bit switch (most of these devices used ARM32 on the stock Android) [I don't have a full overview which devices need this because we have never tested booting mainline Linux with the stock bootloader on most devices]
You also need to be really careful when building the Android boot images. qcom,msm-id/board-ids are not unique, so when you use the typical "dtbTool" building process which bundles all DTBs in arch/arm64/boot/dts you risk device damage. Chances are good that the bootloader will pick the wrong DTB, potentially with wrong regulator voltages or anything like that.
When qcom,msm-id/board-id are missing such mistakes cannot happen because the stock bootloader will just refuse to boot it. Personally I actually consider that to be a good thing because booting with the stock bootloader is almost always a naive mistake made by end users that have no experience with the whole complicated DTB selection story.
I won't object to adding the properties but I also don't really see a use case for them. People porting devices can easily add them when building a custom kernel. End users want the full functionality (including SMP) so if they boot through the stock bootloader it's most likely accidental.
Thanks, Stephan
[1]: https://github.com/msm8916-mainline/lk2nd/tree/master/dts/msm8974/sony [2]: https://github.com/msm8916-mainline/lk2nd/blob/dd850aeb0c348cea085db8013f578615715cdd7f/dts/msm8916/msm8916-motorola-surnia.dts#L21-L32
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