[U-Boot] [PATCH v3 00/62] dm: rockchip: sandbox: Add support for compiled-in platform data

[Simon Glass]

Hi,

On 4 July 2016 at 11:57, Simon Glass <sjg at chromium.org> wrote:
>
> Note: This v3 series adds a test and fixes a few bugs found in generation of
> of-platdata.
>
> This series provides a way to compile in the contents of a device tree as C
> code into U-Boot, implementing an idea that Tom Rini came up with. It is
> intended to deal with extremely tight environments where there is not enough
> space for the ~3KB device tree code overhead. Examples include SPL where
> there is only 16KB of available RAM yet a full MMC stack is required.
>
> To provide a reasonable test environment, SPL support is added to sandbox,
> through a new 'sandbox_spl' target. A new tool 'dtoc' converts device tree
> data to C code (and structure definitions).
>
> To check its effectiveness for a real application, the v2 series includes
> support for enabling of-platdata for a rockchip board (firefly-rk3288). The
> results are as follows:
>
>                           Code       Data      u-boot-spl.bin size
> of-platdata disabled      23159      1624      28864
> of-platdata enabled       19093      2616      21761
>
> Overall the saving is 7103 bytes, about 7KB. Approximately 4KB of this comes
> from removing the device tree data from SPL although this is offset by
> the size of the of-platdata itself (around 1KB). On top of this effective
> 3KB reduction, another ~3KB reduction comes from dropping libfdt and a
> further 1KB from dropping unused setup and driver-model code.
>
> Clearly this approach does have value. Looked at with a favourable light it
> provides the best of both worlds: configuration using standard device tree
> bindings without the run-time overhead.
>
> Looking under the hood shows a less rosy picture. Effectively we end up
> with a new set of C structures which must be handled by the driver. This
> series suggests a suitable approach for dealing with this (see of-plat.txt)
> which is workable. However there are a number of serious caveats. See that
> file for details.
>
> Thsi feature should be used sparingly. Rockchip is to some extent an unusual
> case: lots of features (leading to a large SPL device tree size of 4KB), no
> MMC stack available to SPL from the internal ROM* and a very limited maximum
> SPL code size. Most SoCs will not benefit from this.
>
> However, for an SoC with very small SRAM where only a few drivers are needed
> in SPL (such as serial and MMC) then of-platdata could provide a useful
> benefit, without a significant increase in complexity.
>
> With the v3 series this feature is ready for use. It is available at
> u-boot-dm/dt-working.
>
> The dtoc tool might be better renamed fdttoc (which is clumsy) or fdt2c.
> Ideas welcome.

I'm planning to apply this series soon. Please let me know if there
are any further comments.

Regards,
Simon