[U-Boot] [PATCH 1/3] dm: Add migration plan for CONFIG_BLK

[André Przywara]

Hi,

On 02/04/18 03:30, Simon Glass wrote:
> 
> Hi Andre,
> 
> On 2 April 2018 at 09:43, André Przywara <andre.przywara at arm.com> wrote:
>> Hi,
>>
>> On 01/04/18 14:19, Tom Rini wrote:
>>> On Tue, Mar 27, 2018 at 11:34:19PM +0530, Jagan Teki wrote:
>>>> On Mon, Sep 4, 2017 at 9:57 PM,  <sjg at google.com> wrote:
>>>>> Hi Tom,
>>>>>
>>>>> On 7 August 2017 at 09:39, Tom Rini <trini at konsulko.com> wrote:
>>>>>> On Sat, Aug 05, 2017 at 03:45:53PM -0600, Simon Glass wrote:
>>>>>>
>>>>>>> The CONFIG_BLK conversion involves quite invasive changes in the U-Boot
>>>>>>> code, with #ifdefs and different code paths. We should try to move over to
>>>>>>> this soon so we can drop the old code.
>>>>
>>>> I hope this will applicable to SPL too?
>>>>
>>>> If so, we are having SPL size issues with few Allwinner families, if
>>>> enable SPL_DM any suggestions?
>>>
>>> How close, and have you looked at the u-boot-spl.map to see what you can
>>> maybe trim?  Or areas to look at reducing in code complexity?
>>
>> The Boot ROM limit for all Allwinner SoCs known so far is 32KB. The A64
>> SPL (AArch64) stands at ~31KB at the moment. Yes, we went over the map
>> and picked most low hanging fruits already.
>> So far we discussed several mitigations, but mostly to cover the
>> "natural" SPL code size grow over time:
>> 1) The AArch64 exception vectors take 1KB, plus an unnecessary ~1.6KB of
>> padding (for a 2KB architectural alignment). Given that the vectors are
>> used only for debugging purposes, we could scrap them entirely or
>> construct them on the fly in some other SRAM. So would free about 2.5KB,
>> ideally. Lowest hanging fruit so far.
>> 2) We can compile the SPL in AArch32 mode, which can use the Thumb2
>> encoding. This reduces the size significantly, to about 20KB. The
>> disadvantage is using a second cross-compiler or even a additional
>> cross-compiler for native builds, complicating the build process.
>> I maintain a branch for enabling FEL booting here [1], which provides
>> two _defconfigs (one 32-bit for SPL, one 64-bit for U-Boot proper).
>> There are no technical disadvantages in running the SPL in 32-bit, so
>> this is mostly a build issue.
> 
> FYI 32-bit tegra compiles SPL with ARMv4T and U-Boot proper with
> ARMv7. It should be fairly easy to do,

Yes, but this is merely different compiler *flags*, to the same (cross)
compiler binary. ARM32 and ARM64 are different architectures to GCC, so
require different compiler binaries with different prefixes.
Last time I checked this wasn't easy to integrate into the U-Boot build
system.
One hack could be a "switching script", which filters for, say -m32",
and calls the respective binary. But still we need to somehow set *two*
CROSS_COMPILE prefixes. CROSS_COMPILE_SPL, maybe?
But still it would require to install *two* cross compilers, and would
spoil a completely native build by still requiring a cross compiler.

>> 3) Try to use ILP32 for the AArch64 SPL build. This reduces the pointer
>> size and sizeof(long) to be 32-bit and should help, though I haven't
>> been able to successfully compile it yet (relocation types problems).
>> Despite lacking mainline support for AArch64 ILP32 in Linux and
>> glibc(?), GCC supports it for quite a while already. Unknown saving effect.
>> 4) Use runtime decompression. Most SoCs have larger or more SRAM than
>> the 32KB, so we could leverage this. Siarhei knows more about this.
>> 5) Use a TPL. Haven't looked at this in detail yet.
>>
>> So 1) would be the easiest to pursue, but 2.5KB are not enough to offset
>> the >10 KB toll the DM_SPL support actually takes.
> 
> Is this the cost on 64-bit?

Yes, this is AArch64, just enabling DM_SPL_MMC and DM_SPL.

> I wonder if CONFIG_OF_PLATDATA might be an option?

Well, this would be a requirement, I guess, since adding any kind of DT
to the mix makes it even worse.

Cheers,
Andre