Simon Glass <s...@chromium.org> schrieb am Mi., 22. Mai 2019, 21:34: > Hi Simon, > > On Wed, 22 May 2019 at 02:05, Simon Goldschmidt > <simon.k.r.goldschm...@gmail.com> wrote: > > > > On Wed, May 22, 2019 at 2:53 AM Simon Glass <s...@chromium.org> wrote: > > > > > > Hi Andreas, > > > > > > On Tue, 21 May 2019 at 15:01, Andreas Dannenberg <dannenb...@ti.com> > wrote: > > > > > > > > Hi Simon (Glass), > > > > > > > > On Sat, May 18, 2019 at 10:08:19AM -0600, Simon Glass wrote: > > > > > Hi Andreas, > > > > > > > > > > On Mon, 6 May 2019 at 22:49, Andreas Dannenberg <dannenb...@ti.com> > wrote: > > > > > > > > > > > > Hi Simon, > > > > > > > > > > > > On Mon, May 06, 2019 at 09:51:56PM -0600, Simon Glass wrote: > > > > > > > Hi Andreas, > > > > > > > > > > > > > > On Fri, 3 May 2019 at 14:25, Andreas Dannenberg < > dannenb...@ti.com> wrote: > > > > > > > > > > > > > > > > Simon, > > > > > > > > > > > > > > > > On Sat, Mar 30, 2019 at 09:18:08PM +0100, Simon Goldschmidt > wrote: > > > > > > > > > Simon Glass <s...@chromium.org> schrieb am Sa., 30. März > 2019, 21:06: > > > > > > > > > > > > > > > > > > > Hi Simon, > > > > > > > > > > > > > > > > > > > > On Wed, 27 Mar 2019 at 13:40, Simon Goldschmidt > > > > > > > > > > <simon.k.r.goldschm...@gmail.com> wrote: > > > > > > > > > > > > > > > > > > > > > > This introduces a new Kconfig option SPL_CLEAR_BSS_F. > If enabled, it > > > > > > > > > > clears > > > > > > > > > > > the bss before calling board_init_f() instead of > clearing it before > > > > > > > > > > calling > > > > > > > > > > > board_init_r(). > > > > > > > > > > > > > > > > > > > > > > This also ensures that variables placed in BSS can be > shared between > > > > > > > > > > > board_init_f() and board_init_r() in SPL. > > > > > > > > > > > > > > > > > > > > > > Such global variables are used, for example, when > loading things from FAT > > > > > > > > > > > before SDRAM is available: the full heap required for > FAT uses global > > > > > > > > > > > variables and clearing BSS after board_init_f() would > reset the heap > > > > > > > > > > state. > > > > > > > > > > > An example for such a usage is socfpa_arria10 where an > FPGA configuration > > > > > > > > > > > is required before SDRAM can be used. > > > > > > > > > > > > > > > > > > > > > > Make the new option depend on ARM for now until more > implementations > > > > > > > > > > follow. > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > > I still have objections to this series and I think we > should discuss > > > > > > > > > > other ways of solving this problem. > > > > > > > > > > > > > > > > > > > > Does socfgpa have SRAM that could be used before SDRAM > is available? > > > > > > > > > > If so, can we not use that for the configuration? What > various are > > > > > > > > > > actually in BSS that are needed before board_init_r() is > called? Can > > > > > > > > > > they not be in a struct created from malloc()? > > > > > > > > > > > > > > > > > > > > > > > > > > > > The problem is the board needs to load an FPGA > configuration from FAT > > > > > > > > > before SDRAM is available. Yes, this is loaded into SRAM > of course, but the > > > > > > > > > whole code until that is done uses so many malloc/free > iterations that The > > > > > > > > > simple mall of implementation would require too much > memory. > > > > > > > > > > > > > > > > > > And it's the full malloc state variables only that use > BSS, not the FAT > > > > > > > > > code. > > > > > > > > > > > > > > > > I've actually faced very similar issues working on our TI > AM654x "System > > > > > > > > Firmware Loader" implementation (will post upstream soon), > where I need > > > > > > > > to load this firmware and other files from media such as > MMC/FAT in a very > > > > > > > > memory-constrained SPL pre-relocation environment *before* I > can bring up > > > > > > > > DDR. > > > > > > > > > > > > > > > > Initially, I modified the fat.c driver to re-use memory so > it is not as > > > > > > > > wasteful during SYS_MALLOC_SIMPLE. While I'm not proud of > this solution [1] > > > > > > > > this allowed us to get going, allowing to load multiple > files without > > > > > > > > issues in pre-relocation SPL. > > > > > > > > > > > > > > That seems to point the way to a useful solution I think. We > could > > > > > > > have a struct containing allocated pointers which is private > to FAT, > > > > > > > and just allocate them the first time. > > > > > > > > > > > > The board_init_f()-based loader solution we use extends beyond > MMC/FAT, > > > > > > but also for OSPI, X/Y-Modem, and (later) USB, network, etc. > > > > > > > > > > > > Background: > > > > > > On our "TI K3" devices we need to do a whole bunch of stuff > before > > > > > > DDR is up with limited memory, namely loading and installing a > firmware > > > > > > that controls the entire SoC called "System Firmware". It is > only after > > > > > > this FW is loaded from boot media and successfully started that > I can > > > > > > bring up DDR. So all this is done in SPL board_init_f(), which > as the > > > > > > last step brings up DDR. > > > > > > > > > > > > Not having BSS available to carry over certain state to the > > > > > > board_init_r() world would lead to a bunch of hacky changes > across > > > > > > the board I'm afraid, more below. > > > > > > > > > > This is really unfortunate. > > > > > > > > > > It seems to me that we have two choises: > > > > > > > > > > 1. Hack around with board_init_f() such as to remove the > distinction > > > > > between this and board_init_r(). > > > > > > > > > > 2. Enter board_init_r() without DRAM ready, and deal with setting > it up there. > > > > > > > > > > I feel that the second solution is worth exploring. We could have > some > > > > > board-specific init in board_init_r(). We already have > > > > > spl_board_init() so perhaps we could have spl_early_board_init() > > > > > called right near the top? > > > > > > > > > > We can refactor a few of the functions in spl/spl.c so they can be > > > > > called from board-specific code if necessary. We could also add new > > > > > flags to global_data to control the behaviour of the SPL code, and > the > > > > > board code could set these. > > > > > > > > Let me explore this option. I can probably make something work but I > > > > don't yet see how to do it cleanly, maybe it becomes clearer once I > put > > > > some code down. Currently by definition board_init_r() has DDR > > > > available, and much of the code is geared towards it (for example the > > > > calling of spl_relocate_stack_gd() before entering board_init_r() > which > > > > will already switch over to DDR). > > > > > > > > Also, and not to discourage that we can't improve upon the status > quo, > > > > but there is already a ton of boards using such an "early BSS" > scheme... > > > > > > > > $ git grep --show-function 'memset.*bss' | grep board_init_f | wc -l > > > > 35 > > > > > > Yes I know :-( > > > > > > We should migrate these boards to use the generic SPL framework. > > > > socfpga_gen5 is one of the architectures listed here. I'm not even sure > > whether that's actually needed. However, it's hard to test, isn't it? How > > do you actually tell BSS isn't used before entering board_init_r? > > One way might be to link the SPL code without the call to > board_init_r() and then check the map to make sure BSS is empty. >
That would be worth a try. > > > > To be sure, we'd need to initialize unused memory to some magic > > constant and check that it has been left untouched later (on boards > > where BSS is available in board_init_r and remains in place when > > moving on). > > I prefer a build-time check. We might even be able to automate it. > Of course a build-time check is better here than a runtime check. I just couldn't come up with one. I think it would be really beneficial to add such a check to all boards so we know what we're discussing: I'll bet there are many of them just using bss early because No one noticed... And in board-local code, that could even be ok, it's just not ok for code shared with boards not having access to bss early. Regards, Simon > Regards, > Simon > > > > > Regards, > > Simon > > > > > > > > > > > > > > > > I wonder if that would be enough for > > > > > > > > > > > > > > > > > > > > > > > In the quest of creating something more upstream-friendly I > had then > > > > > > > > switched to using full malloc in pre-relocation SPL so that > I didn't > > > > > > > > have to hack the FAT driver, encountering similar issues > like you > > > > > > > > brought up and got this working, but ultimately abandoned > this > > > > > > > > approach after bundling all files needed to get loaded into > a single > > > > > > > > image tree blob which no longer required any of those > solutions. > > > > > > > > > > > > > > > > What remained till today however is a need to preserve > specific BSS > > > > > > > > state from pre-relocation SPL over to post-relocation SPL > environment, > > > > > > > > namely flags set to avoid the (expensive) re-probing of > peripheral > > > > > > > > drivers by the SPL loader. For that I introduced a Kconfig > option that > > > > > > > > allows skipping the automatic clearing of BSS during > relocation [2]. > > > > > > > > > > > > > > > > Seeing this very related discussion here got me thinking > about how else > > > > > > > > I can carry over this "state" from pre- to post relocation > but that's > > > > > > > > probably a discussion to be had once I post my "System > Firmware Loader > > > > > > > > Series", probably next week. > > > > > > > > > > > > > > Since this is SPL I don't you mean 'relocation' here. I think > you mean > > > > > > > board_init_f() to board_init_r()? > > > > > > > > > > > > Yes that's what I mean. AFAIK relocation in SPL is still called > relocation > > > > > > from what I have seen working on U-boot, it just relocates gd > and stack > > > > > > but not the actual code (personally I find it misleading calling > what SPL > > > > > > does "relocation", but I got used to it). > > > > > > > > > > > > > You can use global_data to store state, > > > > > > > > > > > > I thought the idea was to stay away from gd, so we can > eventually get > > > > > > rid of it altogether? > > > > > > > > > > Not that I know of. It is how we communicate state before we have > BSS. > > > > > > > > Oh ok I see now, I guess I have taken the comment [1] from > > > > arch/arm/lib/spl.c out of context. > > > > > > > > [1] > https://github.com/u-boot/u-boot/blob/master/arch/arm/lib/spl.c#L22 > > > > > > Ah yes. That is referring to putting global_data in the data section. > > > Perhaps we can delete that code now and see what breaks? > > > > > > > > > > > > It is how we communicate state before we have BSS. > > > > > > > > Understood. > > > > > > > > > > > or malloc() to allocate memory and put things there. > > > > > > > > > > > > The challenge with potentially having to incorporate such a > custom > > > > > > solution for state preservation into several drivers as explained > > > > > > earlier (SPI, USB, network, etc.) is that it does not appear to > scale > > > > > > well. I think using BSS instead would make all those additions > cleaner > > > > > > and simpler. > > > > > > > > > > > > > But using BSS seems wrong to me. > > > > > > > > > > > > I've seen you saying this a few times :) > > > > > > Why? > > > > > > > > > > Driver model does its own allocate of memory and this is all > attached > > > > > to the DM structures. > > > > > > > > > > Drivers themselves cannot assume they are the only instance > running, > > > > > so data should be attached to their private-data pointers. > Similarly > > > > > for uclasses, if we put everything in the uclass-private data, > then we > > > > > don't need BSS and don't have any problems dealing with whether it > is > > > > > available yet. In general, BSS creates a lot of problems early in > > > > > U-Boot's execution, and we don't actually need to use it. > > > > > > > > Yes, understood. The DM concept with private-data pointers is quite > > > > clean from an OOP point of view. > > > > > > > > > If you look at the DM design you'll see that we try to avoid > malloc() > > > > > and BSS as much as possible. I suppose this series is another > example > > > > > of why :-) > > > > > > > > > > > > > > > > > > If you are doing something in board_init_f() in SPL that needs > BSS, > > > > > > > can you not just move that code to board_init_r()? > > > > > > > > > > > > I need to access media drivers in board_init_f(), for which > currently > > > > > > I'm using BSS so I can preserve some limited state, such as that > the > > > > > > peripheral init was done, so that it doesn't get re-done by the > actual > > > > > > SPL loader later. board_init_r() requires DDR to be available > which I > > > > > > can't use without doing all that work in board_init_f() first to > > > > > > load/start the system controller firmware, so it's a bit of a > chicken > > > > > > and egg issue here. > > > > > > > > > > Let's try moving the egg into board_init_r() and putting the > chicken > > > > > after it, as mentioned above. > > > > > > > > Well I'll give this a shot. > > > > > > > > > > > > > > > > My system firmware loader patch series is about ready and I was > planning > > > > > > on posting it tomorrow. How about with the entire approach being > in the > > > > > > open we use this as an opportunity to re-look at potential > alternative > > > > > > solutions... > > > > > > > > > > Sure. I hope I've explained my POV above. > > > > > > > > Yes thanks for the review and comments. > > > > > > You're welcome, and good luck with it. > > > > > > Regards, > > > Simon > _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot
