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

Fri Apr 19 12:34:29 CEST 2024

On 18/04/24 17:30, Sughosh Ganu wrote:
> On Thu, 18 Apr 2024 at 16:08, Chintan Vankar <c-vankar at ti.com> wrote:
>>
>>
>>
>> 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 at 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?
>>>
>>
>> Sughosh,
>>
>> I think my explanation was not clear at:
>> "We are trying to boot AM62x using Ethernet for which we need to load
>> binary files at SPL and U-Boot stage using TFTP."
>> - In Ethernet Booting we are fetching U-Boot image at SPL stage via
>> TFTP at specified address 0x82000000. While loading U-Boot image we are
>> getting TFTP error, since address from stack pointer till gd->ram_top is
>> reserved due to "lmb_init_and_reserve()" function call. I want to know
>> for which purpose this address range is reserved.
> 
> On relocation, the U-Boot image is located typically at the top of the
> DRAM memory used by U-Boot(ram_top). That region of memory is reserved
> to ensure that the memory occupied by the U-Boot image does not get
> overwritten by a LMB reservation.
>

Yes, you are correct about U-Boot relocation but we are facing an issue
at the time of fetching U-Boot proper at SPL stage.

> Btw, are you facing this issue in SPL, or U-Boot proper? I built the
> images for the am62x_evm_a53 config, and I don't see the

We are getting "TFTP error" at runtime while fetching U-Boot proper at
SPL stage while booting via "Ethernet", and we are using
"am62x_evm_a53_ethboot_defconfig" instead of "am62x_evm_a53_defconfig".

These are the extra configs we are using on top of
"am62x_evm_a53_defconfig":

CONFIG_SPL_DRIVERS_MISC=y
CONFIG_SPL_BOARD_INIT=y
CONFIG_SPL_DMA=y
CONFIG_SPL_ENV_SUPPORT=y
CONFIG_SPL_ETH=y
CONFIG_SPL_NET=y
CONFIG_SPL_NET_VCI_STRING="AM62X U-Boot A53 SPL"
CONFIG_SPL_SYSCON=y

> arch_lmb_reserve() function getting included in the SPL image -- both
> the .text.arch_lmb_reserve and .text.arch_lmb_reserve_generic are part
> of discarded sections. So I am wondering how you are observing this
> behaviour in SPL.
> 
> -sughosh
> 
>>
>>> 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 tried this approach of assigning a higher address for SPL stack, but
>> it is not working as expected.