Re: Removal of qcom,board-id and qcom,msm-id
From: Konrad Dybcio
Date: Mon May 23 2022 - 08:02:45 EST
On 23/05/2022 09:21, Krzysztof Kozlowski wrote:
On 22/05/2022 21:51, Konrad Dybcio wrote:
Hi,
removing these properties will not bring almost any benefit (other than making
some checks happy any saving some <200 LoC) and will make the lives of almost
all people doing independent development for linux-on-msm harder. There are
almost unironically like 3 people outside Linaro and QUIC who have
non-vendor-fused development boards AND the sources to rebuild the
bootloader on their own. Making it harder to boot is only going to
discourage people from developing on these devices, which is already not
that pleasant, especially with newer platforms where you have to fight with
the oh-so-bright ideas of Android boot chain..
This only concerns devices released before sm8350, as the new ones will not
even boot with these properties present (or at least SONY Sagami, but I
doubt it's an isolated case), so other than completing support for older
devices, it won't be an issue going forward, anyway. But there are give
or take 50 locked down devices in mainline right now, and many more waiting
to be upstreamed in various downstream close-to-mainline trees that should
not be disregarded just because Qualcomm is far from the best at making
their BSP software stack clean.
I actually wonder why do you need these properties for community work on
such boards? You ship kernel with one concatenated DTB and the
bootloader does not need the board-id/msm-id fields, doesn't it?
If that were the case, I would have never complained about this! It's
the bootloader itself that needs it, you can see it in a "Best match
[blah blah] 258/0x1000/...." log line, where it walks through the
appended (or otherwise compiled into the boot.img) DTBs and looks for
matches for the burnt-in msm-, board- and (on newer-older platforms)
pmic-id. If it cannot find these, it refuses to boot with an Android
Verified Boot red state and you get a not-so-nice "Your device has been
unlocked and the boot image is not working" or something like this on
your screen.
Not mentioning that in the past bootloader was actually not using these
properties at all, because it was the dtbTool who was parsing them.
Not sure when that was the case, maybe with very old arm32 bootloaders
in the times before I did development on Qualcomm devices.
So
in any case either your device works fine without these properties or
you have to use dtbTool, right?
To the best of my idea, wrong :( Unless the vendor modified the LK/XBL
code on their own, it looks for a "best match" (but if it's not a
precise match, it won't even bother trying to boot, just fyi..), meaning
it tries to go through a list of SoC ID and revision pairs (msm-id),
board IDs (board-id) and PMIC id+rev pairs (pmic-id) and if no match is
found, it doesn't even exit the bootloader and says something like "no
dtbs found".
And hence, they are absolutely necessary one way or another.
Konrad
One solution is to chainload another, (n+1)-stage bootloader, but this is
not ideal, as:
1) the stock bootloader can boot Linux just fine on most devices (except
for single exceptions, where beloved OEMs didn't implement arm64 booting or
something)
2) the boot chain on MSM is already 3- or 4- stage and adding to that will
only create an unnecessary mess
3) the job of kernel people is not to break userspace. If the
device can not even exit bootloader after a kernel upgrade, it's a big
failure.
The job of kernel people is to follow bindings and since they were
introduced 7 years ago, I would say there was plenty of time for that.
If the dtbTool support for the bindings is there, then there is no
breakage, because you had to use dtbTool before so you have to use now.
If you *really really really* want these either gone or documented, we can
for example use them in the SOCID driver, read the values from DTB and
compare against what SMEM has to say and for example print a warning when
there are inconsistencies or use it as a fallback when it fails for any
reason, such as using a newer SoC on an older kernel, without updates
for SOCID read (which are sometimes necessary, which was the case for 8450
recently, iirc).
My stance is to just leave them as is, as moving them anywhere, or removing
them at all will cause unnecessary mess and waste time that could have been
spent on more glaring issues..
Konrad
Best regards,
Krzysztof