[U-Boot] [PATCH v2 2/3] spl: add relocation support【请注意，邮件由sjg at google.com代发】

[Andy Yan]

Hi Simon:

Simon Glass <sjg at chromium.org> 于2019年5月22日周三 上午8:28写道：

> Hi Andy,
>
> On Tue, 21 May 2019 at 00:51, Andy Yan <andy.yan at rock-chips.com> wrote:
> >
> > Hi Simon:
> >
> > On 2019/5/20 下午11:35, Simon Glass wrote:
> > > Hi Andy,
> > >
> > > On Mon, 20 May 2019 at 00:34, Andy Yan <andy.yan at rock-chips.com>
> wrote:
> > >> Hi Simon:
> > >>
> > >> On 2019/5/19 上午12:26, Simon Glass wrote:
> > >>> Hi Andy,
> > >>>
> > >>> Instead of this could you:
> > >>>
> > >>> - move ATF?
> > >> All rockchip based arm64 ATF run from the start 64KB of dram as this
> > >> will give convenient for kernel manage the memory.
> > >>
> > >> On the other hand, change the ATF load address will break the
> > >> compatibility of the exiting firmware.
> > >>
> > >>> - change the SPL load address so it is not in the way (since TPL can
> > >>> load to any address)
> > >> The SPL is loaded by bootrom after TPL back to bootrom, so the load
> > >> address if fixed by bootrom code.
> > > I think you are creating a nightmare here. If you have to do things
> > > like this for older and smaller SoCs, OK. But it should not be used
> > > for newer ones that can do things properly.
> >
> >
> > Most rockchip based SOC sram is small,  even in the future soc roadmap,
> > this situation  will still exist, larger sram means more cost.
>
> I believe the RK3399 has 192KB. What is the minimum size in new chips?
>

The sram size of RK3328 is 32KB, and now the u-boot-tpl.bin of rk3328
without storage drive is 28KB.
The available sram size for TPL on RK3326 is 10KB,  our another A35 based
IOT SOC has the same limitation.


>
> >
> > As for the current spl for rockchip soc in mainline, we use a workaround
> > by reserve large space at the head of spl(see
> > CONFIG_ROCKCHIP_SPL_RESERVE_IRAM ), this generate a very large spl
> binary.
>
> Yes.
>
> >
> > As for my patch, the spl relocation is disabled default, we only enable
> > it on necessary platform, so it won't hurt others .
>
> Well it adds more code and complexity. Perhaps it makes sense to add
> this, but I want to understand the need.
>
> >
> > > The bootrom has so many limitations that it just creates pain.
> > >
> > >> I know we can build mmc or other storage driver into TPL so we can use
> > >> tpl load spl on some platform that sram is big enough, but there are
> > >> also many rockchip soc has very small sram, so we tend to only do dram
> > >> initialization in tpl, and let bootrom load next stage .
> > > See above
> > >
> > For the consideration of software development, we also want to keep TPL
> > clean,  only do dram initialization(as it current status), this make our
> > internal dram team work more simple, they don't need to care about other
> > modules like mmc.
>
> Yes I understand this, but the boot ROM should be provided as a
> library to call into:
>
> int mmc_read(void *addr, int start_block, int end_block)
> int spi_read(void *addr, int start_block, int end_block)
>
> Then SPL or TPL can use it without all the strange limitations we have now.
>
> Since you probably already have these functions somewhere in the boot
> ROM, you could implement this using a function table somewhere in the
> ROM with a magic number before it, so that SPL can find it.
>

The Bootrom do much more work than directly load the spl binary. It will do
somthing like checksum, look for the backup when the current image is
invalid, also including security check when secure boot is enabled. This is
why we did much work to add back_too_bootrom   mechanism in mainline in
2017.

>
> >
> >
> > >>> - (in extremis) create a function which does a memmove() and a jump,
> > >>> copy it somewhere and run it (I think x86 does this)
> > > ?
> > I am not very understand about this, just a memmove may not work, we
> > need to link the code by pie, and fix the rela.dyn sections after copy.
> > see arm/relocate_64.S
>
> Well if you don't access absolute addresses (which you generally don't
> in ARM) your memmove() and jump code should be relocatable.
>
> Also I wonder what you think of Andre's solution?
>
>
 See my reply .

> [..]
>
> Regards
> Simon
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