On Wed, May 18, 2022 at 03:19:19PM +0200, Pali Rohár wrote: > On Wednesday 18 May 2022 08:19:36 Tom Rini wrote: > > On Wed, May 18, 2022 at 02:17:39PM +0200, Pali Rohár wrote: > > > On Wednesday 18 May 2022 08:16:55 Tom Rini wrote: > > > > On Wed, May 18, 2022 at 12:58:38PM +0200, Pali Rohár wrote: > > > > > On Tuesday 17 May 2022 12:38:43 Tom Rini wrote: > > > > > > On Tue, May 17, 2022 at 06:00:16PM +0200, Pali Rohár wrote: > > > > > > > On Tuesday 17 May 2022 11:52:14 Tom Rini wrote: > > > > > > > > On Mon, May 16, 2022 at 11:56:51PM +0200, Pali Rohár wrote: > > > > > > > > > On Monday 16 May 2022 08:31:43 Tom Rini wrote: > > > > > > > > > > On Sat, May 14, 2022 at 01:00:06AM +0200, Pali Rohár wrote: > > > > > > > > > > > > > > > > > > > > > Hello! I tried to enable support for 2GB+ of DDR memory > > > > > > > > > > > (with 4GB DDR3) > > > > > > > > > > > on powerpc P2020 board in 32-bit addressing mode and > > > > > > > > > > > U-Boot crashed > > > > > > > > > > > during startup. > > > > > > > > > > > > > > > > > > > > > > I figured out that issue is not powerpc specific, but > > > > > > > > > > > rather generic to > > > > > > > > > > > all 32-bit platforms. U-Boot stores memory size into > > > > > > > > > > > phys_size_t type > > > > > > > > > > > (gd->ram_size) and last mapped memory address increased > > > > > > > > > > > by one byte into > > > > > > > > > > > phys_addr_t type (gd->ram_top). > > > > > > > > > > > > > > > > > > > > > > Despite size 4GB fits into 32-bit addressing mode, it > > > > > > > > > > > does not fit into > > > > > > > > > > > above two variables, and it overflows to zero. U-Boot > > > > > > > > > > > then see zero RAM > > > > > > > > > > > size and crashes. > > > > > > > > > > > > > > > > > > > > > > I tried to workaround this issue by changing both > > > > > > > > > > > phys_size_t and > > > > > > > > > > > phys_addr_t types to 64-bit. But it did not helped > > > > > > > > > > > because U-Boot on > > > > > > > > > > > many places cast gd->ram_size or gd->ram_top to ulong > > > > > > > > > > > type, which is > > > > > > > > > > > 32-bit on 32-bit platforms. > > > > > > > > > > > > > > > > > > > > > > Next I changed ulong parameters of > > > > > > > > > > > board_get_usable_ram_top() function > > > > > > > > > > > to u64. > > > > > > > > > > > > > > > > > > > > > > This still was not enough because config value > > > > > > > > > > > CONFIG_MAX_MEM_MAPPED is > > > > > > > > > > > ignored on one important place -- in function > > > > > > > > > > > get_effective_memsize(). > > > > > > > > > > > This config value takes effect only when also > > > > > > > > > > > CONFIG_VERY_BIG_RAM is > > > > > > > > > > > set. > > > > > > > > > > > > > > > > > > > > > > Finally With this change I was able to start U-Boot with > > > > > > > > > > > more than 2GB > > > > > > > > > > > of DDR memory inserted in SODIMM slot on P2020. > > > > > > > > > > > > > > > > > > > > > > How to fix issues with gd->ram_size and gd->ram_top? That > > > > > > > > > > > +1 byte is > > > > > > > > > > > really stupid limitation. Changing phys_size_t and > > > > > > > > > > > phys_addr_t types > > > > > > > > > > > unconditionally to 64-bit? Or something else? > > > > > > > > > > > > > > > > > > > > > > And what is the purpose of CONFIG_VERY_BIG_RAM config > > > > > > > > > > > option? Why is > > > > > > > > > > > CONFIG_MAX_MEM_MAPPED check skipped in > > > > > > > > > > > get_effective_memsize() function, > > > > > > > > > > > but is not skipped on many more places? > > > > > > > > > > > > > > > > > > > > So, there's two parts to this, as I recall it all. First, > > > > > > > > > > even on 64bit > > > > > > > > > > platforms we contain ourselves to 32bit address space and > > > > > > > > > > even then > > > > > > > > > > something within the "old" 2GB window. We then set a > > > > > > > > > > CONFIG option to > > > > > > > > > > not mess with the memory node in DT which has the real > > > > > > > > > > value. Second, > > > > > > > > > > for 32bit platforms which can support 4GB memory, or more, > > > > > > > > > > some further > > > > > > > > > > games need to be played, typically I believe around > > > > > > > > > > initializing the > > > > > > > > > > memory controller (I'm more confident of that for > > > > > > > > > > dra7xx_evm, which I > > > > > > > > > > don't have the big memory version of, just a small memory > > > > > > > > > > one) so that > > > > > > > > > > Linux can do whatever needs doing to enable "36bit" > > > > > > > > > > typically address > > > > > > > > > > support. Looking at the other P*36BIT* configs might give > > > > > > > > > > you some more > > > > > > > > > > clues about what to do on your platform, or at least who > > > > > > > > > > might still be > > > > > > > > > > able to explain and test things on the PowerPC side. > > > > > > > > > > > > > > > > > > I know about 36-bit addressing on e500v2 but I'm not going to > > > > > > > > > enable it > > > > > > > > > due to performance reasons (see Freescale AN4064 [1]). So I > > > > > > > > > want to > > > > > > > > > stick with 32-bit addressing for 2GB+ memory usage (around > > > > > > > > > 3GB; it is > > > > > > > > > 4GB minus memory used by peripherals; which is still more > > > > > > > > > than 2GB). > > > > > > > > > > > > > > > > > > And due to 32-bit type for phys_size_t, phys_addr_t and > > > > > > > > > casting these > > > > > > > > > types to ulong is an issue. Plus issue with > > > > > > > > > CONFIG_VERY_BIG_RAM and > > > > > > > > > CONFIG_MAX_MEM_MAPPED as I already wrote. > > > > > > > > > > > > > > > > I'm not seeing the problem, sorry. You run U-Boot in the > > > > > > > > normal 2GB > > > > > > > > > > > > > > Ok, I will try to explain it again. > > > > > > > > > > > > > > I want to run U-Boot in normal 2GB area. U-Boot normally store > > > > > > > detected > > > > > > > RAM size into the gd->ram_size structure. And here is the issue. > > > > > > > > > > > > > > 32-bit unsigned C type cannot represent maximal 32-bit > > > > > > > addressable size. > > > > > > > U-Boot tries to store 4GB value = 0x100000000 into gd->ram_size > > > > > > > which > > > > > > > overflows to 0x00000000. And U-Boot then crashes because it > > > > > > > expects that > > > > > > > can store some data at address "gd->ram_size - few_kb" as it > > > > > > > expects > > > > > > > that RAM is in the area [0, gd->ram_size). > > > > > > > > > > > > > > It is more clear what is the problem? > > > > > > > > > > > > > > If I theoretically find 3.9GB RAM module (but such probably does > > > > > > > not > > > > > > > exist) then U-Boot should work in normal 2GB area as number 3.9GB > > > > > > > can be > > > > > > > stored into 32-bit unsigned type. > > > > > > > > > > > > Yes, you need to disable CONFIG_ARCH_FIXUP_FDT_MEMORY > > > > > > > > > > CONFIG_ARCH_FIXUP_FDT_MEMORY affects booting OS. > > > > > > > > > > The issue is that **u-boot** is crashing during its initialization. > > > > > > > > When configuring the controller for 4GB, but limiting U-Boot to 2GB? > > > > > > Yes! > > > > Interesting. Maybe you just have to do the 36BIT games on that SoC, to > > support what you're trying to do. If anyone at NXP knows something > > perhaps they'll chime in. > > Why? It is issue in U-Boot and affects all 32-bit platforms not only > powerpc/NXP.
I disagree. It's working as intended with other 32bit platforms, unless it's stopped working on dra7xx_evm with >2GB memory (which I don't have, unfortunately). If you can't configure the memory controller to know that 4GB exists, but limit yourself to running within 2GB, that's a SoC-specific problem. If you want to make the big changes so that we can have a larger than 2GB memory space for U-Boot, period, that's a big general change with challenges as you've already seen. -- Tom
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