Hi Simon,

On 2/7/20 18:10, Simon Glass wrote:
This series provides a proposed enhancement to driver model to reduce
overhead in SPL.

These patches should not be reviewed other than to comment on the
approach. The code is all lumped together in a few patches and so cannot
be applied as is.

For now, the source tree is available at:

    https://gitlab.denx.de/u-boot/custodians/u-boot-dm/-/tree/dtoc-working

Comments welcome!

Benefits (good news)
--------------------

As an example of the impact of tiny-dm, chromebook_jerry is converted to
use it. This shows approximately a 30% reduction in code and data size and
a 85% reduction in malloc() space over of-platdata:

    text           data     bss     dec     hex filename
   25248           1836      12   27096    69d8 spl/u-boot-spl (original with 
DT)
   19727           3436      12   23175    5a87 spl/u-boot-spl (OF_PLATDATA)
     78%    187%    100%     86%         as %age of original

   13784           1408      12   15204    3b64 spl/u-boot-spl (SPL_TINY)
     70%     41%    100%     66%         as %age of platdata
     55%     77%    100%     56%         as %age of original

SPL malloc() usage drops from 944 bytes (OF_PLATDATA) to 116 (SPL_TINY).

Overall the 'overhead' of tiny-dm is much less than the full driver
model. Code size is currently about 600 bytes for these functions on
Thumb2:

    00000054 T tiny_dev_probe
    00000034 T tiny_dev_get_by_drvdata
    00000024 T tiny_dev_find
    0000001a T tiny_dev_get
    0000003c T tinydev_alloc_data
    0000002a t tinydev_lookup_data
    00000022 T tinydev_ensure_data
    00000014 T tinydev_get_data
    00000004 T tinydev_get_parent

Effort (bad news)
-----------------

Unfortunately it is quite a bit of work to convert drivers over to
tiny-dm. First, the of-platdata conversion must be done. But on top of
that, tiny-dm needs entirely separate code for dealing with devices. This
means that instead of 'struct udevice' and 'struct uclass' there is just
'struct tinydev'. Each driver and uclass must be modified to support
both, pulling common code into internal static functions.

Another option
--------------

Note: It is assumed that any board that is space-contrained should use
of-platdata in SPL (see doc/driver-model/of-plat.rst). This is shown to
reduce device-tree overhead by approximately 4KB.

Designing tiny-dm has suggested a number of things that could be changed
in the current driver model to make it more space-efficient for TPL and
SPL. The ones with least impact on driver code are (CS=reduces code size,
DS=reduces data size):

    CS - drop driver_bind() and create devices (struct udevice) at
         build-time
    CS - allocate all device- and uclass-private data at build-time
    CS - remove all but the basic operations for each uclass (e.g. SPI
         flash only supports reading)
    DS - use 8-bit indexes instead of 32/64-bit pointers for device
         pointers possible since these are created at build-time)
    DS - use singly-linked lists
    DS - use 16-bit offsets to private data, instead of 32/64-bit pointers
         (possible since it is all in SRAM relative to malloc() base,
         presumably word-aligned and < 256KB)
    DS - move private pointers into a separate data structure so that NULLs
         are not stored
    CS / DS - Combine req_seq and seq and calculate the new value at
         build-time

More difficult are:

    DS - drop some of the lesser-used driver and uclass methods
    DS - drop all uclass methods except init()
    DS - drop all driver methods except probe()
    CS / DS - drop uclasses and require drivers to manually call uclass
         functions

Even with all of this we would not reach tiny-dm and it would muddy up the
driver-model datas structures. But we might come close to tiny-dm on size
and there are some advantages:

- much of the benefit would apply to all boards that use of-platdata (i.e.
   with very little effort on behalf of board maintainers)
- the impact on the code base is much less (we keep a single, unified
   driver mode in SPL and U-Boot proper)

Overall I think it is worth looking at this option. While it doesn't have
the 'nuclear' impact of tiny-dm, neither does it mess with the U-Boot
driver code as much and it is easier to learn.

Thanks for your hard work on this topic.

I think that there is great value in this research and in this conclusion. It is clear that there two different approaches, but I feel that the improvement to  the current DM implementation would have a higher impact in the community.

Since the first version of this proposal I have been thinking in a solution that takes some of the advantages of tiny-dm idea but that does not require so much effort. This seems to be aligned with what you have been explaining in this section.

I found interesting your proposal about simplification some data structures. In this sense one of my ideas, a bit biased by some of the improvements in dtoc, is to change the the definition of struct driver based on if OF_PLATDATA is enabled, and in this case remove some properties.

struct driver {
#if !CONFIG_IS_ENABLED(OF_PLATDATA)
        char *name;
#endif
        enum uclass_id id;
#if !CONFIG_IS_ENABLED(OF_PLATDATA)
        const struct udevice_id *of_match;
#endif
        int (*bind)(struct udevice *dev);
        int (*probe)(struct udevice *dev);
        int (*remove)(struct udevice *dev);
        int (*unbind)(struct udevice *dev);
        int (*ofdata_to_platdata)(struct udevice *dev);
        int (*child_post_bind)(struct udevice *dev);
        int (*child_pre_probe)(struct udevice *dev);
        int (*child_post_remove)(struct udevice *dev);
        int priv_auto_alloc_size;
        int platdata_auto_alloc_size;
        int per_child_auto_alloc_size;
        int per_child_platdata_auto_alloc_size;
        const void *ops;        /* driver-specific operations */
        uint32_t flags;
#if CONFIG_IS_ENABLED(ACPIGEN)
        struct acpi_ops *acpi_ops;
#endif
};

By just removing those properties, we save some bytes as we get rid of several strings. Also maybe it would be nice to add some macros to make it cleaner in drivers to use or not those properties, instead of adding lots of #if.

I feel, as you clearly expressed, that some additional refactotring can be made to make the logic be more similar to the tiny-dm one. I also found interesting that several of your proposals will have impact in U-Boot, not only in TPL/SPL.

Changes in v2:
- Various updates, and ported to chromebook_jerry (rockchip)

Simon Glass (3):
   dm: Driver and uclass changes for tiny-dm
   dm: Arch-specific changes for tiny-dm
   dm: Core changes for tiny-dm

  arch/arm/dts/rk3288-u-boot.dtsi               |  17 +-
  arch/arm/dts/rk3288-veyron.dtsi               |  26 +-
  arch/arm/dts/rk3288.dtsi                      |   3 +
  arch/arm/include/asm/arch-rockchip/clock.h    |   9 +
  .../include/asm/arch-rockchip/sdram_rk3288.h  |  21 ++
  arch/arm/include/asm/arch-rockchip/spi.h      |   1 +
  arch/arm/include/asm/io.h                     |  18 +
  arch/arm/mach-rockchip/rk3288/clk_rk3288.c    |  46 +++
  arch/arm/mach-rockchip/rk3288/rk3288.c        |   2 +
  arch/arm/mach-rockchip/rk3288/syscon_rk3288.c |  45 +--
  arch/arm/mach-rockchip/sdram.c                |  33 +-
  arch/sandbox/cpu/u-boot-spl.lds               |  12 +
  arch/sandbox/dts/sandbox.dts                  |   3 +-
  arch/sandbox/dts/sandbox.dtsi                 |   2 +-
  arch/x86/cpu/apollolake/cpu_spl.c             |   5 +-
  arch/x86/cpu/apollolake/uart.c                |  56 ++++
  arch/x86/dts/chromebook_coral.dts             |   1 +
  arch/x86/lib/tpl.c                            |   4 +-
  board/Synology/ds109/ds109.c                  |   3 +-
  common/console.c                              |   2 +-
  common/log.c                                  |  36 +-
  common/malloc_simple.c                        |  31 ++
  common/spl/spl.c                              |  17 +-
  common/spl/spl_spi.c                          |  91 +++--
  configs/chromebook_coral_defconfig            |   1 +
  configs/chromebook_jerry_defconfig            |  11 +
  configs/rock2_defconfig                       |   3 +
  doc/develop/debugging.rst                     |  35 ++
  doc/driver-model/tiny-dm.rst                  | 315 +++++++++++++++++
  drivers/clk/Kconfig                           |  54 +++
  drivers/clk/Makefile                          |   4 +-
  drivers/clk/clk-uclass.c                      |  53 ++-
  drivers/clk/rockchip/clk_rk3288.c             | 106 ++++--
  drivers/core/Kconfig                          | 106 ++++++
  drivers/core/Makefile                         |   3 +
  drivers/core/of_extra.c                       |  49 ++-
  drivers/core/regmap.c                         |   3 +-
  drivers/core/syscon-uclass.c                  |  68 +++-
  drivers/core/tiny.c                           | 249 ++++++++++++++
  drivers/mtd/spi/Kconfig                       |  18 +
  drivers/mtd/spi/sf-uclass.c                   |  76 +++++
  drivers/mtd/spi/sf_probe.c                    |   4 +
  drivers/mtd/spi/spi-nor-tiny.c                | 166 ++++++++-
  drivers/ram/Kconfig                           |  18 +
  drivers/ram/ram-uclass.c                      |  12 +
  drivers/ram/rockchip/sdram_rk3188.c           |   2 +-
  drivers/ram/rockchip/sdram_rk322x.c           |   2 +-
  drivers/ram/rockchip/sdram_rk3288.c           | 231 ++++++++-----
  drivers/ram/rockchip/sdram_rk3328.c           |   2 +-
  drivers/ram/rockchip/sdram_rk3399.c           |   2 +-
  drivers/reset/reset-rockchip.c                |   4 +-
  drivers/serial/Kconfig                        |  38 +++
  drivers/serial/ns16550.c                      | 195 +++++++++--
  drivers/serial/sandbox.c                      |  59 +++-
  drivers/serial/serial-uclass.c                |  77 +++++
  drivers/serial/serial_omap.c                  |   2 +-
  drivers/serial/serial_rockchip.c              |  59 ++++
  drivers/spi/Kconfig                           |  18 +
  drivers/spi/Makefile                          |   2 +
  drivers/spi/rk_spi.c                          | 301 ++++++++++++-----
  drivers/spi/spi-uclass.c                      |  77 +++++
  drivers/sysreset/Kconfig                      |  18 +
  drivers/sysreset/sysreset-uclass.c            | 124 ++++---
  drivers/sysreset/sysreset_rockchip.c          |  61 +++-
  include/asm-generic/global_data.h             |   7 +-
  include/clk-uclass.h                          |  11 +
  include/clk.h                                 |  32 +-
  include/dm/device.h                           | 121 +++++++
  include/dm/of_extra.h                         |   6 +
  include/dm/platdata.h                         |  20 +-
  include/dm/tiny_struct.h                      |  42 +++
  include/linker_lists.h                        |   6 +
  include/linux/mtd/mtd.h                       |  23 +-
  include/linux/mtd/spi-nor.h                   |  22 ++
  include/log.h                                 |   6 +
  include/malloc.h                              |   3 +
  include/ns16550.h                             |   7 +-
  include/ram.h                                 |  25 ++
  include/regmap.h                              |   4 +-
  include/serial.h                              |  45 ++-
  include/spi.h                                 |  31 ++
  include/spi_flash.h                           |   7 +
  include/spl.h                                 |   8 +-
  include/syscon.h                              |   2 +
  include/sysreset.h                            |   9 +
  scripts/Makefile.spl                          |   6 +-
  tools/dtoc/dtb_platdata.py                    | 316 +++++++++++++++---
  tools/dtoc/dtoc_test_simple.dts               |  12 +-
  tools/dtoc/fdt.py                             |   7 +-
  tools/dtoc/main.py                            |   9 +-
  tools/dtoc/test_dtoc.py                       |  91 ++++-
  tools/patman/tools.py                         |   4 +-
  92 files changed, 3454 insertions(+), 540 deletions(-)
  create mode 100644 doc/develop/debugging.rst
  create mode 100644 doc/driver-model/tiny-dm.rst
  create mode 100644 drivers/core/tiny.c
  create mode 100644 include/dm/tiny_struct.h

Regards,

Walter

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