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

[Chintan Vankar <c-vankar@ti.com>]

On 17/04/24 21:34, Tom Rini wrote:
> On Wed, Apr 17, 2024 at 05:48:31PM +0530, Sughosh Ganu wrote:
>> hi Chintan,
>>
>> On Wed, 17 Apr 2024 at 13:21, Chintan Vankar <c-vankar@ti.com> wrote:
>>>
>>>
>>>
>>> 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()".
>>
>> I have no idea about your platform but I was wondering if there is any
>> particular importance of the load address of 0x82000000? It looks as
>> though the current location of the SP when arch_lmb_reserve() gets
>> called means that the load address is getting reserved for the U-Boot
>> image. Do you not have the option of loading the image at a lower
>> address instead?
> 
> Or using a higher address for SPL stack? You might be able to solve this
> just by re-examining which addresses (and RAM size limitations) need to
> be considered here.
> 

Tom,

We changed SPL_STACK_R_ADDR to higher address as you suggested here and
observe that the memory area which was getting reserved by
"lmb_init_and_reserve()" function, when SPL_STACK_R_ADDR was 0x82000000,
is from 0x81FFB820 to gd->ram_top, but when SPL_STACK_R_ADDR is changed
to 0x83000000, stack pointer is pointing to 0x82FFB810 and reserving a
memory area till gd->ram_top. Since memory address 0x82000000 is not
there in reserved memory area region U-Boot proper is successfully
getting fetched and we are able to boot.

Can it be considered of changing "SPL_STACK_R_ADDR" independently for
Ethernet Boot feature ?