[U-Boot] [PATCH v3 8/9] tegra: i2c: Enable new CONFIG_SYS_I2C framework

[Simon Glass]

Hi Albert,

On Thu, Aug 1, 2013 at 2:16 PM, Albert ARIBAUD <albert.u.boot at aribaud.net>wrote:

> Hi Simon,
>
> On Thu, 1 Aug 2013 08:22:55 -0600, Simon Glass <sjg at chromium.org> wrote:
>
> > Hi,
> >
> > On Thu, Aug 1, 2013 at 2:38 AM, Heiko Schocher <hs at denx.de> wrote:
> >
> > > Hello Albert,
> > >
> > > Am 01.08.2013 08:53, schrieb Albert ARIBAUD:
> > >
> > >  Hi Heiko,
> > >>
> > >> On Thu, 01 Aug 2013 08:02:42 +0200, Heiko Schocher<hs at denx.de>
>  wrote:
> > >>
> > >>  I suppose you could. It seems conceptually /far/ simpler to just scan
> > >>>> the DT once up-front rather than having to defer all this stuff
> until
> > >>>>
> > >>>
> > >>> on the other hand we ring for every ms boot time ... and here we want
> > >>> to scan a complete dt with maybe a lot of nodes, we do not want to
> > >>> use?
> > >>>
> > >>
> > >> Scanning all of DT seems to imply it has no strict or standard
> > >> ordering. Could we mandate, suggest, of make it so that all entries in
> > >> the DT needed at _f time are put first, and even maybe place an "end
> of
> > >> _f" custom marker in DT to delimit them? (I assume that, for the sake
> of
> > >>
> > >
> > > I do not know, if this is possible, as I think the DT used in U-Boot
> > > should be the same as used in linux ... or?
> > >
> > >
> > >  Postel-ism, anything in DT which is not understandable is skipped, so
> > >> other users of the DT than us would not even be annoyed by such a
> > >> marker)
> > >>
> > >> This way, we'd avoid wasting time scanning most of the DT in this
> case.
> > >>
> > >
> > > Hmm.. why should we introduce such things, instead of scanning the
> > > node only if we need it?
> > >
> > > We have "only" the problem, that we could not write to data at this
> > > moment ... but this problem should be solved in a seperate topic.
> > > I2C is usable before relocation, the problem is in conjunction with
> > > dt, that we can not save for example the base address of the
> controller,
> > > which we get from the DT ... If I understand it correct!
> > >
> > > So we need an option when using dt, that we have (small ram) in which
> > > we can write some parameters parsed from dt ...
> > >
> > > I think this problem have all subsystems used before relocation.
> > > (for example: environment on a spi flash?)
> > >
> > >
> > I think using a small RAM is a good approach. At least it is better than
> > pretending there is no RAM at all. We currently have no facility to
> > allocate RAM before relocation, other than to use the .data section. We
> can
> > use global_data but that won't scale well for many drivers adding their
> own
> > stuff in there. Samsung's driver uses .data, I don't think it is a big
> deal.
>
> What about targets which do not have such a small RAM available?
>

Presumably such targets do not use SPL, and perhaps don't use FDT at
present?


>
> > One option I should mention is to decode the I2C FDT nodes each time it
> is
> > needed prior to relocation (i.e. to the stack), use it for the
> transaction,
> > and throw it away. This is quite painful IMO this it involves putting
> calls
> > in the driver to check if we are pre-reloc and have a stack space used
> > every time. On tegra20 this would be 130 bytes or so. I mention it
> because
> > console working this way for a while (decoding the console again on every
> > byte).
> >
> > Options as I see it:
> >
> > - just fudge it for now and use .data (deal with it later with driver
> model)
> > - change the meaning of board_init_f() such that memory may be available
> > (e.g. if run from SPL)
> > - decode the FDT nodes every time we need them (ick)
> > - adjust the ordering so that I2C normally happens post reloc except for
> > specific platforms with a CONFIG defined (Heiko, the difference as I
> > understand it is that with your patch CONFIG_HARD_I2C or CONFIG_SOFT_I2C
> > are now defined, and so I2C happens prior to reloc now)
> >
> >
> > >
> > > As Wolfgang said:
> > > "Agreed - actually we're entering an area hear that smells pretty
> > > strong like device model reorganization :-)"
> > >
> > > BTW: How is this problem solved with the device model approach?
> >
> >
> > More that we need to solve it, probably with a limited malloc()
> pre-reloc.
>
>
Regards,
Simon