[U-Boot] [PATCH 00/16] RFC: Board init using driver model

[Simon Glass]

Hi Tom,

On 22 March 2017 at 08:37, Tom Rini <trini at konsulko.com> wrote:
> On Wed, Mar 22, 2017 at 07:05:38AM -0600, Simon Glass wrote:
>> Hi Tom,
>>
>> On 19 March 2017 at 18:47, Tom Rini <trini at konsulko.com> wrote:
>> > On Sun, Mar 19, 2017 at 12:59:19PM -0600, Simon Glass wrote:
>> >> At present we have a lot of ad-hoc init functions related to boards, for
>> >> example board_early_init_f(), board_misc_init_f() and dram_init().
>> >>
>> >> There are used in different ways by different boards as useful hooks to
>> >> do the required init and sequence it correctly. Some functions are always
>> >> enabled but have a __weak default. Some are controlled by the existence
>> >> of a CONFIG.
>> >>
>> >> There are two main init sequences: board_init_f() (f for running from
>> >> read-only flash) which runs before relocation and board_init_r() (r for
>> >> relocated) which runs afterwards.
>> >>
>> >> One problem with the current sequence is that it has a lot of
>> >> arch-specific #ifdefs around various functions. There are also #ifdefs
>> >> for various features. There has been quite a bit of discussion about how
>> >> to tidy this up and at least one RFC series[1].
>> >>
>> >> Now that we have driver model we can use this to deal with the init
>> >> sequences. This approach has several advantages:
>> >>
>> >> - We have a path to remove the #ifdefs
>> >> - It is easy for multiple parts of the code to implement the same hook
>> >> - We can track what is called and what is not
>> >> - We don't need weak functions
>> >> - We can eventually adjust the sequence to improve naming or to add new
>> >> init phases
>> >> - It provides a model for how we might deal with ft_board_setup() and
>> >> friends
>> >>
>> >> This series starts the process of replacing the pre-relocation init
>> >> sequence with a driver-model solution. It defines a uclass, adds tests
>> >> and converts sandbox and a few x86 boards over to use this new setup.
>> >>
>> >> This series is not ready for use yet as the rest of the init sequence
>> >> hooks need to be converted. But there is enough here to show the idea.
>> >>
>> >> Comments welcome.
>> >>
>> >> [1] https://lists.denx.de/pipermail/u-boot/2011-August/098718.html
>> >
>> > How does this look, size wise?  With all of these conversions and
>> > clean-ups, we really need to be size concious as well as it all keeps
>> > adding up.  Thanks!
>>
>> It include size a bit - e.g. x86 808 bytes of text, although that does
>> include a few extra features.
>
> How about if we don't include some of the extra debug/demo type features
> (which are useful at times, certainly) ?  We keep adding things that add
> a few bytes here and a few bytes there and it all adds up.

Yes it's very important that the base version doesn't increase size,
or at least only minimally. I should have examined that more closely
in the RFC - my intent was really to get comments on the approach,

>
> [snip]
>> I think I can use a linker-list approach to reduce the overhead. But I
>> still think the driver has value as it provides a means of adding
>> hooks to do board-specific things from drivers, something that we keep
>> running into. Also the idea of a board 'driver' seems conceptually
>> useful.
>>
>> So one approach would be to have:
>>
>> 1. A linker-list-based board hook setup, where you can declare, for example:
>>
>> static int ivybridge_dram_init(void)
>> {
>>  ...
>> }
>> U_BOOT_BOARD_HOOK(ivybridge_dram_init, BOARD_F_DRAM_INIT);
>>
>> This should be pretty cheap, perhaps <200 bytes with some care.
>>
>>
>> 2. An optional BOARD uclass which can be used for more involved
>> situations, but with a higher code size penalty.
>
> OK.  But I also recall that we had talked about trying to condense and
> re-factor things.  My worry about an approach like this is it allows for
> us to more easily get back into the bad habits of having each
> architecture solve similar problems with different solutions.

Yes that's true and I've been pushing back on this for a while. For
example there is quite a bit of pressure to add board-specific init
code to drivers with driver model. So far I think we have been able to
avoid this using device tree and other drivers. For example if MMC
needs a clock we can find the required clock by phandle and call the
clock driver.

So are you thinking we should limit this to just a simple hook
approach for now, and then consider the board uclass down the track?

Regards,
Simon