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

[Tom Rini]

On Wed, Mar 22, 2017 at 08:43:54AM -0600, Simon Glass wrote:
> 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?

Looking over init_sequence_[rf], I can certainly see the case for "ug,
this is ugly and we need to make it better" (and I now wonder if we
don't have a lot more places where we need INIT_FUNC_WATCHDOG_RESET,
anyhow...).  But for the moment we seem to be able to resist adding more
calls here.  And I would like to see if we can rework / reduce the
current table before we try and simplify and clean-up the mechanism that
we use to handle them.

-- 
Tom
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