>> (Tom - any thoughts about a more expansive cc list on this?) >> >> Hi Masahiro, >> >> On 26 November 2017 at 07:16, Masahiro Yamada >> <yamada.masah...@socionext.com> wrote: >> > 2017-11-26 20:38 GMT+09:00 Simon Glass <s...@chromium.org>: >> >> Hi Philipp, >> >> >> >> On 25 November 2017 at 16:31, Dr. Philipp Tomsich >> >> <philipp.toms...@theobroma-systems.com> wrote: >> >>> Hi, >> >>> >> >>>> On 25 Nov 2017, at 23:34, Simon Glass <s...@chromium.org> wrote: >> >>>> >> >>>> +Tom, Masahiro, Philipp >> >>>> >> >>>> Hi, >> >>>> >> >>>> On 22 November 2017 at 03:27, Wolfgang Denk <w...@denx.de> wrote: >> >>>>> Dear Kever Yang, >> >>>>> >> >>>>> In message >> >>>>> <fd0bb500-80c4-f317-cc18-f7aaf1344...@rock-chips.com> you >> >>>>> wrote: >> >>>>>> >> >>>>>> I can understand this feature, we always do dram_init_banks() >> >>>>>> first, then we relocate to 'known' area, then will be no risk >> >>>>>> to access memory. I believe there must be some historical >> >>>>>> reason for some kind of device, the relocate feature is a >> >>>>>> wonderful idea for it. >> >>>>> >> >>>>> This is actuallyu not so much a feature needed to support some >> >>>>> specific device (in this case much simpler approahces would be >> >>>>> possible), but to support a whole set of features. >> >>>>> Unfortunately these appear to get forgotten / ignored over time. >> >>>>> >> >>>>>> many other SoCs should be similar. >> >>>>>> - Without relocate we can save many step, some of our customer >> >>>>>> really care much about the boot time duration. >> >>>>>> * no need to relocate everything >> >>>>>> * no need to copy all the code >> >>>>>> * no need init the driver more than once >> >>>>> >> >>>>> Please have a look at the README, section "Memory Management". >> >>>>> The reloaction is not done to any _fixed_ address, but the >> >>>>> address is actually computed at runtime, depending on a number >> >>>>> features enabled (at least this is how it used to be - >> >>>>> appearently little of this is tested on a regular base, so I >> >>>>> would not be surprised if things are broken today). >> >>>>> >> >>>>> The basic idea was to reserve areas of memory at the top of RAM, >> >>>>> that would not be initialized / modified by U-Boot and Linux, >> >>>>> not even across a reset / warm boot. >> >>>>> >> >>>>> This was used for exaple for: >> >>>>> >> >>>>> - pRAM (Protected RAM) which could be used to store all kind of >> >>>>> data (for example, using a pramfs [Protected and Persistent RAM >> >>>>> Filesystem]) that could be kept across reboots of the OS. >> >>>>> >> >>>>> - shared frame buffer / video memory. U-Boot and Linux would be >> >>>>> able to initialize the video memory just once (in U-Boot) and >> >>>>> then share it, maybe even across reboots. especially, this >> >>>>> would allow for a very early splash screen that gets passed >> >>>>> (flicker free) to Linux until some Linux GUI takes over (much >> >>>>> more difficult today). >> >>>>> >> >>>>> - shared log buffer: U-Boot and Linux used to use the same >> >>>>> syslog buffer mechanism, so you could share it between U-Boot >> >>>>> and Linux. this allows for example to >> >>>>> * read the Linux kernel panic messages after reset in U-Boot; >> >>>>> this is very useful when you bring up a new system and Linux >> >>>>> crashes before it can display the log buffer on the console >> >>>>> * pass U-Boot POST results on to Linux, so the application code >> >>>>> can read and process these >> >>>>> * process the system log of the previous run (especially after >> >>>>> a panic) in Lunux after it rebootet. >> >>>>> >> >>>>> etc. >> >>>>> >> >>>>> There are a number of such features which require to reserve >> >>>>> room at the top of RAM, the size of which is calculatedat >> >>>>> runtime, often depending on user settable environment data. >> >>>>> >> >>>>> All this cannot be done without relocation to a (dynmaically >> >>>>> computed) target address. >> >>>>> >> >>>>> >> >>>>> Yes, the code could be simpler and faster without that - but >> >>>>> then, you cut off a number of features. >> >>>> >> >>>> I would be interested in seeing benchmarks showing the cost of >> >>>> relocation in terms of boot time. Last time I did this was on >> >>>> Exynos 5 and it was some years ago. The time was pretty small >> >>>> provided the cache was on for the memory copies associated with >> >>>> relocation itself. Something like 10-20ms but I don't have the >> >>>> numbers handy. >> >>>> >> >>>> I think it is useful to be able to allocate memory in >> >>>> board_init_f() for use by U-Boot for things like the display and >> >>>> the malloc() region. >> >>>> >> >>>> Options we might consider: >> >>>> >> >>>> 1. Don't relocate the code and data. Thus we could avoid the >> >>>> copy and relocation cost. This is already supported with the >> >>>> GD_FLG_SKIP_RELOC used when U-Boot runs as an EFI app >> >>>> >> >>>> 2. Rather than throwing away the old malloc() region, keep it >> >>>> around so existing allocated blocks work. Then new malloc() >> >>>> region would be used for future allocations. We could perhaps >> >>>> ignore free() calls in that region >> >>>> >> >>>> 2a. This would allow us to avoid re-init of driver model in most >> >>>> cases I think. E.g. we could init serial and timer before >> >>>> relocation and leave them inited after relocation. We could just >> >>>> init the 'additional' devices not done before relocation. >> >>>> >> >>>> 2b. I suppose we could even extend this to SPL if we wanted to. I >> >>>> suspect it would just be a pain though, since SPL might use >> >>>> memory that U-Boot wants. >> >>>> >> >>>> 3. We could turn on the cache earlier. This removes most of the >> >>>> boot-time penalty. Ideally this should be turned on in SPL and >> >>>> perhaps redone in U-Boot which has more memory available. If SPL >> >>>> is not used, we could turn on the cache before relocation. >> >>> >> >>> Both turning on the cache and initialising the clocking could be >> >>> of benefit to boot-time. >> >>> >> >>> However, the biggest possible gain will come from utilising >> >>> Falcon mode to skip the full U-Boot stage and directly boot into >> >>> the OS from SPL. This assumes that the drivers involved are >> >>> fully optimised, so loading up the OS image does not take longer >> >>> than necessary. >> >> >> >> I'd like to see numbers on that. From my experience, loading and >> >> running U-Boot does not take very long... >> >> >> >>> >> >>>> 4. Rather than the reserving memory in board_init_f() we could >> >>>> have it call malloc() from the expanded region. We could then >> >>>> perhaps then move this reserve/allocate code in to particular >> >>>> drivers or subsystems, and drop a good chunk of the init >> >>>> sequence. We would need to have a larger malloc() region than is >> >>>> currently the case. >> >>>> >> >>>> There are still some arch-specific bits in board_init_f() which >> >>>> make these sorts of changes a bit tricky to support generically. >> >>>> IMO it would be best to move to 'generic relocation' written in >> >>>> C, where all archs work basically the same way, before >> >>>> attempting any of the above. >> >>>> >> >>>> Still, I can see some benefits and even some simplifications. >> >>>> >> >>>> Regards, >> >>>> Simon >> >>> >> > >> > >> > >> > This discussion should have happened. >> > U-Boot boot sequence is crazily inefficient. >> > >> > >> > >> > When we talk about "relocation", two things are happening. >> > >> > [1] U-Boot proper copies itself to the very end of DRAM >> > [2] Fix-up the global symbols >> > >> > In my opinion, only [2] is useful. >> > >> > >> > SPL initializes the DRAM, so it knows the base and size of DRAM. >> > SPL should be able to load the U-Boot proper to the final >> > destination. So, [1] is unnecessary. >> > >> > >> > [2] is necessary because SPL may load the U-Boot proper >> > to a different place than CONFIG_SYS_TEXT_BASE. >> > This feature is useful for platforms >> > whose DRAM base/size is only known at run-time. >> > (Of course, it should be user-configurable by CONFIG_RELOCATE >> > or something.) >> > >> > Moreover, board_init_f() is unneeded - >> > everything in board_init_f() is already done by SPL. >> > Multiple-time DM initialization is really inefficient and ugly. >> > >> > >> > The following is how the ideal boot loader would work. >> > >> > >> > Requirement for U-Boot proper: >> > U-Boot never changes the location by itself. >> > So, SPL or a vendor loader must load U-Boot proper >> > to the final destination directly. >> > (You can load it to the very end of DRAM if you like, >> > but the actual place does not matter here.) >> > >> > >> > Boot sequence of U-Boot proper: >> > If CONFIG_RELOCATE (or something) is enabled, >> > it fixes the global symbols at the very beginning >> > of the boot. >> > (In this case, CONFIG_SYS_TEXT_BASE can be arbitrary) >> > >> > That's it. Proceed to the rest of init code. >> > (= board_init_r) >> > board_init_f() is unnecessary. >> > >> > This should work for recent platforms. >> >> Yes that sounds reasonable to me. >> >> We could do the symbol fixup/relocation in SPL after loading U-Boot., >> although that would probably push us to using ELF format for U-Boot >> which is a bit limited. >> >> Still I think the biggest performance improvement comes from turning >> on the cache in SPL. So the above is a simplification, not really a >> speed-up. >> >> > >> > >> > >> > We should think about old platforms that boot from a NOR flash or >> > something. There are two solutions: >> > - execute-in-place: run the code in the flash directly >> > - use SPL (common/spl/spl-nor.c) if you want to run >> > it from RAM >> >> This seems like a big regression in functionality. For example for x86 >> 32-bit we currently don't have an SPL (we do for 64-bit). So I think >> this means that everything would be forced to have an SPL? >> >> I am wondering who else we should cc on this discussion? > > Not all boards use SPL. There are some targets, which use FBL (SPL > counterpart) from vendor and only U-boot proper. Good example is Odroid > XU3.
Some aarch64 boards like Jetson TX series and Dragonboard chain load u-boot from some other loader, things like qemu support I don't believe use SPL either. _______________________________________________ U-Boot mailing list U-Boot@lists.denx.de https://lists.denx.de/listinfo/u-boot