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

[Tom Rini <trini@konsulko.com>]

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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

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