[PATCH 01/10] board: ti: am62x: Init DRAM size in R5/A53 SPL

[Chintan Vankar]

On 16/04/24 22:30, Tom Rini wrote:
> On Tue, Apr 16, 2024 at 05:52:58PM +0530, Chintan Vankar wrote:
>>
>>
>> On 12/04/24 03:37, Tom Rini wrote:
>>> On Wed, Apr 03, 2024 at 06:18:01PM +0530, Chintan Vankar wrote:
>>>>
>>>>
>>>> On 22/01/24 10:11, Siddharth Vadapalli wrote:
>>>>>
>>>>>
>>>>> On 20/01/24 22:11, Tom Rini wrote:
>>>>>> On Mon, Jan 15, 2024 at 01:42:51PM +0530, Siddharth Vadapalli wrote:
>>>>>>> Hello Tom,
>>>>>>>
>>>>>>> On 12/01/24 18:56, Tom Rini wrote:
>>>>>
>>>>> ...
>>>>>
>>>>>>>> The list of conditionals in common/spl/spl.c::board_init_r() should be
>>>>>>>> updated and probably use SPL_NET as the option to check for.
>>>>>>>
>>>>>>> Thank you for reviewing the patch and pointing this out. I wasn't aware of it. I
>>>>>>> assume that you are referring to the following change:
>>>>>>>
>>>>>>>            if (IS_ENABLED(CONFIG_SPL_OS_BOOT) || CONFIG_IS_ENABLED(HANDOFF) ||
>>>>>>> -           IS_ENABLED(CONFIG_SPL_ATF))
>>>>>>> +           IS_ENABLED(CONFIG_SPL_ATF) || IS_ENABLED(CONFIG_SPL_NET))
>>>>>>>                    dram_init_banksize();
>>>>>>>
>>>>>>> I shall replace the current patch with the above change in the v2 series. Since
>>>>>>> this is in the common section, is there a generic reason I could provide in the
>>>>>>> commit message rather than the existing commit message which seems to be board
>>>>>>> specific? Also, I hope that the above change will not cause regressions for
>>>>>>> other non-TI devices. Please let me know.
>>>>>>
>>>>>> Yes, that's the area, and just note that networking also requires the
>>>>>> DDR to be initialized.
>>>>>>
>>>>>
>>>>> Thank you for confirming and providing your suggestion for the contents of the
>>>>> commit message.
>>>>>
>>>> Following Tom's Suggestion of adding CONFIG_SPL_NET in common/spl/spl.c
>>>> "dram_init_banksize()", the issue of fetching a file at SPL stage seemed
>>>> to be fixed. However the commit "ba20b2443c29", which sets gd->ram_top
>>>> for the very first time in "spl_enable_cache()" results in
>>>> "arch_lmb_reserve()" function reserving memory region from Stack pointer
>>>> at "0x81FFB820" to gd->ram_top pointing to "0x100000000". Previously
>>>> when gd->ram_top was zero "arch_lmb_reserve()" was noop. Now using TFTP
>>>> to fetch U-Boot image at SPL stage results in "tftp_init_load_addr()"
>>>> function call that invokes "arch_lmb_reserve()" function, which reserves
>>>> entire memory starting from Stack Pointer to gd->ram_top leaving no
>>>> space to load U-Boot image via TFTP since TFTP loads files at pre
>>>> configured memory address at "0x82000000".
>>>>
>>>> As a workaround for this issue, one solution we can propose is to
>>>> disable the checks "lmb_get_free_size()" at SPL and U-Boot stage. For
>>>> that we can define a new config option for LMB reserve checks as
>>>> "SPL_LMB". This config will be enable by default for the backword
>>>> compatibility and disable for our use case at SPL and U-Boot stage.
>>>
>>> The problem here is that we need LMB for booting an OS, which is
>>> something we'll want in SPL in non-cortex-R cases too, which means this
>>> platform, so that's a no-go. I think you need to dig harder and see if
>>> you can correct the logic somewhere so that we don't over reserve?
>>>
>> Since this issue is due to function call "lmb_init_and_reserve()"
>> function invoked from "tftp_init_load_addr()" function. This function
>> is defined by Simon in commit "a156c47e39ad", which fixes
>> "CVE-2018-18439" to prevent overwriting reserved memory. Simon, can you
>> explain why do we need to call "lmb_init_and_reserve()" function here ?
> 
> This is indeed a tricky area which is why Sughosh is looking in to
> trying to re-work the LMB mechanic and we've had a few long threads
> about it as well.
> 
> I've honestly forgotten the use case you have here, can you please
> remind us?
> 
We are trying to boot AM62x using Ethernet for which we need to load
binary files at SPL and U-Boot stage using TFTP. To store the file we
need a free memory in RAM, specifically we are storing these files at
0x82000000. But we are facing an issue while loading the file since
the memory area having an address 0x82000000 is reserved due to
"lmb_init_and_reserve()" function call. This function is called in
"tftp_init_load_addr()" function which is getting called exactly before
we are trying to get the free memory area by calling
"lmb_get_free_size()".