On Tue, Dec 17, 2024 at 04:42:26PM -0700, Simon Glass wrote:
Hi Tom,
On Tue, 17 Dec 2024 at 13:15, Tom Rini trini@konsulko.com wrote:
On Tue, Dec 17, 2024 at 12:45:46PM -0700, Simon Glass wrote:
Hi Tom,
On Mon, 16 Dec 2024 at 21:00, Tom Rini trini@konsulko.com wrote:
On Sun, Dec 15, 2024 at 05:25:24PM -0700, Simon Glass wrote:
Hi Tom,
On Fri, 13 Dec 2024 at 10:07, Tom Rini trini@konsulko.com wrote:
On Fri, Dec 13, 2024 at 07:32:24AM -0700, Simon Glass wrote: > Hi Tom, > > On Thu, 12 Dec 2024 at 08:11, Tom Rini trini@konsulko.com wrote: > > > > Introduce an option to control if we expect that a prior stage has > > created a bloblist already and thus it is safe to scan the address. We > > need to have this be configurable because we do not (and cannot) know
if
> > the address at CONFIG_BLOBLIST_ADDR is in regular DRAM or some special > > on-chip memory and so it may or may not be safe to read from this > > address this early. > > > > Signed-off-by: Tom Rini trini@konsulko.com > > --- > > Cc: Simon Glass sjg@chromium.org > > --- > > common/Kconfig | 32 ++++++++++++++++++++++++++++++++ > > lib/fdtdec.c | 11 +++-------- > > 2 files changed, 35 insertions(+), 8 deletions(-) > > > > Since this is the essentially the same as my OF_BLOBLIST patch, which > was rejected: > > NAK > > The issue is not whether some 'previous stage' set up a bloblist. For > example, if VPL_BLOBLIST_PRIOR_STAGE is enabled, that presumably means > that TPL set it up. But it doesn't mean that TPL put the FDT in there.
This is wrong. The root problem is saying that the bloblist is in possibly uninitialized memory. The code is quite happy to NOT find the device tree in the bloblist and continue searching other paths.
But until the bloblist is set up, it doesn't exist.
An almost philosophical statement, yes. How should the generic code know if it exists, or does not exist? That is the question.
U-Boot code 'knows', since if this is the first phase which enables CONFIG_IS_ENABLED(BLOBLOST), then the bloblist is available before/after relocation as well as after RAM setup in SPL.
And when U-Boot isn't the first stage?
The only case where that matters is for the devicetree, so we have OF_BLOBLIST to control whether U-Boot looks for it. Eventually we can drop BLOBLIST_FIXED and use registers, perhaps even on x86, which will make things easier.
The only reason it ever matters is if you're picking memory that's not always accessible. Which is a bad choice and should be avoided whenever possible and practical. Which it is here.
We should not be looking for a bloblist that we know is not there yet. The bloblist is set up by bloblist_init(). You seem to be imputing your own semantics for bloblist.
We don't know if the bloblist exists or not. That's the problem. It could already exist. That's the whole reason we're in this particular argument.
See above.
Yes, you seem to be missing the case where U-Boot isn't the first stage.
I really can't see how you came to that conclusion. Just enable OF_BLOBLIST - in fact we can enable it for almost all boards today and it won't harm anything.
I mean, there's very few places using BLOBLIST today. But we can't enable OF_BLOBLIST for any of them unless we say that the BLOBLIST exists in always accessible memory. And that wouldn't be most of them.
In SPL, init happens in board_init_r(), i.e. after RAM is set up. So don't look in the bloblist until it is set up! It doesn't exist.
Unless of course it was setup before. We don't know if it was setup before or not until we look. A big part of the problem is that for prior to U-Boot bloblist we don't need to use main DRAM, the bloblist is tiny and we have some other persistent memory available. Unfortunately, x86 does not.
The only situation where this matters is for the devicetree, which I why i created OF_BLOBLIST, a way to indicate that the bloblist should be checked for a devicetree.
Yes, you keep looking at this from the wrong direction and seem to have backed yourself in to a corner. Why are you insisting that for the normal use case of memory infos and maybe display parameters we need to carve out a hunk of main memory? A bloblist is perfectly capable of NOT containing things. We can avoid having to care about what phase of things we're in too.
Devicetree is the only 'strange' thing here because we need to look at it early.
Device tree is also "strange" in that it's the only thing we read (not write) today prior to U-Boot too from bloblist.
For Raymond's patch, it shouldn't need any conditions.
Yes, and I replied to him that way too.
In U-Boot proper, we look for it before relocation, so we can relocate and expand it for use with ACPI tables, etc.
I'm not sure that's relevant. This means we've taken what we were passed at a fixed address and allocated more space for it and are using it somewhere else.
Yes
Take a look at this patch, too:
3d6531803e1 bloblist: Support initing from multiple places
I'm not sure it's relevant. It does show we have a problem of not knowing if the bloblist exists, or not. And I don't think we're solving that right today (nor does v1 of my patch).
OK
An alternative here would be to better document the requirements of BLOBLIST_ADDR, and then just disable it on chromebook_coral until someone is inclined to move DDR init in to TPL, or someone finds a non-main-memory address to use for BLOBLIST_ADDR or switches to using BLOBLIST_ALLOC.
Coral's TPL runs in cache-as-ram, with a 30KB limit on code size. It cannot do DDR init in TPL because the DDR blob is large (160KB?) and there is a ton of setup to do first, in any case. When CAR goes away, its memory vanishes, so you need to have copied the bloblist somewhere else (the bloblist holds the MRC data which needs to be written to SPI flash later on, when possible). This all works perfectly and there is really no need to change anything.
Ah, so there's some of the details finally. And oh goodness, we're writing to the SPI flash on each boot? That's not good for longevity...
It writes a sector each time, across an area which can hold quite a few writes. It only writes when the details change, so it is fine. This algorithm has worked in the field for years across tens of millions of devices and is common on x86.
To be clear, I wasn't saying that its your design.
No, it isn't my design, but I would be happy if it were. You were suggesting it had a longevity problem, so I wanted to explain it.
Again, you seem to be imputing semantics to bloblist which don't exist.
Unfortunately some things were missed along the way, and are still missing.
Well we should have started from OF_BLOBLIST and then dealt with problems as they came up. In fact, so far there are no problems which it can't solve.
As it is, we have Raymond sending a patch to push the prior-stage mess into TPM, for reasons which make no sense to me. It is just adding confusion.
One other thing we would have likely done by now if my patch[1] had gone in a year ago, is moving away from BLOBLIST_FIXED to using a register protocol. That is more deterministic.
Regards, Simon
[1] https://patchwork.ozlabs.org/project/uboot/patch/20230830180524.315916-31-sj...
I think once again your obsession with OF_BLOBLIST and device tree is causing you to miss everything else. Today we can take a *bloblist* via register. Linaro wrote that, even. The next problem really is that we can't pass that bloblist along to the next stage because all of the U-Boot side of things assumes fixed address.
Perhaps if we had applied OF_BLOBLIST a year ago, so my special 3 ancient chromebooks that nobody cares about or uses apart from me, worked, we could have got bloblist to where it should be today. You are missing the big picture, but stopping me from pursuing it.
I am disappointed that it is only at this stage that you have shown any interest in getting my special 3 ancient chromebooks running.
And I am disappointed that it's only at this stage there's an understanding of what the actual problem is with your special 3 ancient chromebooks. Everything last year was read by me as you arguing that you need a way to control passing the device tree because that's where the device tree is: https://patchwork.ozlabs.org/project/uboot/patch/20230830180524.315916-31-sj... And if not every at least most of your other replies in that thread are about how device tree is passed in. This is why I assumed that your boards were working after having a way to enforce that the device tree comes from bloblist.
So if there's some "big picture" about bloblist being delayed, it is because once again your vision isn't communicated to everyone else you're trying to work with and that is the big problem.