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.
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.
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.
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.
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...