Re: [PATCH v1] common/memsize.c: Fix get_ram_size() original data restore

[Emanuele Ghidoli <ghidoliemanuele@gmail.com>]

On 2/27/26 11:13, Francis, Neha wrote:
> 
> 
> On 2/26/2026 10:01 PM, Tom Rini wrote:
>> On Thu, Feb 26, 2026 at 05:30:06PM +0100, Stefan Eichenberger wrote:
>>> Hi Francesco and Tom,
>>>
>>> On Thu, Feb 26, 2026 at 05:11:49PM +0100, Francesco Dolcini wrote:
>>>> +Emanuele
>>>>
>>>> Hello Tom,
>>>>
>>>> On Thu, Feb 26, 2026 at 08:23:45AM -0600, Tom Rini wrote:
>>>>> On Thu, Feb 26, 2026 at 08:05:02AM +0100, Francesco Dolcini wrote:
>>>>>> Hello Tom,
>>>>>>
>>>>>> On Fri, Mar 14, 2025 at 11:06:49AM +0100, Stefan Eichenberger wrote:
>>>>>>> From: Stefan Eichenberger <stefan.eichenberger@toradex.com>
>>>>>>>
>>>>>>> The get_ram_size() function fails to restore the original RAM data when
>>>>>>> the data cache is enabled. This issue was observed on an AM625 R5 SPL
>>>>>>> with 512MB of RAM and is a regression that became visible with
>>>>>>> commit bc07851897bd ("board: ti: Pull redundant DDR functions to a common
>>>>>>> location and Fixup DDR size when ECC is enabled").
>>>>>>>
>>>>>>> Observed boot failure messages:
>>>>>>>   Warning: Did not detect image signing certificate. Skipping authentication to prevent boot failure. This will fail on Security Enforcing(HS-SE) devices
>>>>>>>   Authentication passed
>>>>>>>   Starting ATF on ARM64 core...
>>>>>>>
>>>>>>> The system then hangs. This indicates that without a data cache flush,
>>>>>>> data in the cache is not coherent with RAM, preventing the system from
>>>>>>> booting. This was verified by printing the content of this address when
>>>>>>> the issue occurs.
>>>>>>>
>>>>>>> Add a data cache flush after each restore operation to resolve this
>>>>>>> issue.
>>>>>>>
>>>>>>> Fixes: bc07851897bd ("board: ti: Pull redundant DDR functions to a common location and Fixup DDR size when ECC is enabled")
>>>>>>> Fixes: 1c64b98c1ec4 ("common/memsize.c: Fix get_ram_size() when cache is enabled")
>>>>>>> Signed-off-by: Stefan Eichenberger <stefan.eichenberger@toradex.com>
>>>>>>
>>>>>> Tom, can we merge this?
>>>>>> This is the last bit to solve the regression reported here,
>>>>>> https://lore.kernel.org/all/20260224152405.GD340942@francesco-nb/
>>>>>
>>>>> I wasn't happy with this at the time, and Stefan's last email in the
>>>>> thread left me with the impression more investigation was needed and
>>>>> likely something else was the root cause.
>>>>
>>>> I believe that this patch is needed.
>>>>
>>>> On AM62 what is happening is the following.
>>>>
>>>> We have a cortex-R5 that is the first core booting (there is also a
>>>> cortex-m4, but it's not relevant for this discussion).
>>>>
>>>> It runs from internal memory and it configures the DDR ram
>>>>
>>>> We load to DDR memory various pieces of firmware (TFA, U-Boot for the
>>>> cortex A53, ...)
>>>>
>>>> We do execute get_ram_size(), that read/write the memory, and it is
>>>> supposed to restore it back the original content
>>>>
>>>> However when we have the cache enabled, we might miss to write back the
>>>> original memory content, where the other pieces of firmware are.
>>>>
>>>> And after that we start the cortex A53, running in DDR, and there the
>>>> memory content might not be correct, because there is no cache coherency
>>>> between the cortex-A and the cortex-R. And because of that we have
>>>> crashes.
>>>>
>>>> Stefan: any comment here? Can you help?
>>>
>>> I think what you wrote summarises the issue well. If I recall correctly,
>>> I "fixed" the issue last time by simply calling get_ram_size() once
>>> before enabling the cache. This was in commit 4164289db882e. The SPL
>>> then informs U-Boot of the memory size via fdt fixup. However, something
>>> has probably changed now (possibly in the R5 SPL), meaning the cache is
>>> enabled earlier, so the cache is enabled again when get_ram_size() is
>>> called.
>>>
>>> For the AMP use case, either "get_ram_size" should not be called once
>>> the cache is enabled, or a similar patch to the one I proposed is
>>> required.
>>
>> I would lean towards the former if at all possible.
>>
> 
> Just trying to understand, what is the reasoning behind ensuring get_ram_size is
> not called if cache is not enabled? Wasn't get_ram_size written with the
> possibility of cache being enabled (existence of dcache_en logic); then this
> patch is a valid fix right?
> 
> In parallel, I do agree we need to have a code analysis w.r.t dram_init, we are
> making certain cache and dram calls spuriously making this confusing.
> 

Hello Tom,
I agree with Francis.

When I proposed commit 1c64b98c1ec4 ("common/memsize.c: Fix get_ram_size()
when cache is enabled"), I was not considering the presence of other actors
(other cores, DMA engines, etc.).

That patch fixes what I had overlooked at the time. We need to restore the
actual RAM contents, not only what is perceived by the core executing
get_ram_size().

To me this patch sounds intrinsically correct.

Thank you and kind regards,
Emanuele