[U-Boot] is it mandatory for SPL to support DM

[Tom Rini]

On Mon, May 25, 2020 at 09:48:29PM +0200, Marek Vasut wrote:
> On 5/25/20 9:28 PM, Tom Rini wrote:
> > On Mon, May 25, 2020 at 09:07:54PM +0200, Marek Vasut wrote:
> >> On 5/25/20 7:32 PM, Tom Rini wrote:
> >>> On Mon, May 25, 2020 at 10:58:12PM +0530, Jagan Teki wrote:
> >>>> On Mon, May 25, 2020 at 9:06 PM Simon Glass <sjg at chromium.org> wrote:
> >>>>>
> >>>>> Hi,
> >>>>>
> >>>>> On Mon, 25 May 2020 at 04:35, Marek Vasut <marex at denx.de> wrote:
> >>>>>>
> >>>>>> On 5/25/20 10:44 AM, Jagan Teki wrote:
> >>>>>>> SPL has a foot-print constraint, so fully switching a particular
> >>>>>>> subsystem like SPI or SPI Flash to DM would increase the size of it.
> >>>>>>>
> >>>>>>> Possible areas to look at are (assume SPL_DM supported)
> >>>>>>> 1) platdata
> >>>>>>> 2) implement board or platform specific spl device driver which
> >>>>>>> bypassed the actual framework ex: spl_spi_sunxi.c
> >>>>>>>
> >>>>>>> Do we have any other solutions? or any arguments on above step 2?
> >>>>>>
> >>>>>> SPL does not need to support DM until the size problem is solved.
> >>>>>
> >>>>> I don't think the problem will ever be 'solved'. It is an ongoing battle.
> >>>>>
> >>>>> But as it happens I've just sent a proposal for tiny-dm that I think will help.
> >>>>>
> >>>>> Jagan, which board are you trying to convert? If you are trying to
> >>>>> convert SPI flash, I think we need to remove the legacy code first.
> >>>>
> >>>> These are the partially dm converted drivers, so boards which are
> >>>> using can eventually need a dm spi switch.
> >>>>
> >>>>         drivers/spi/fsl_dspi.c
> >>>>         drivers/spi/kirkwood_spi.c
> >>>>         drivers/spi/mxc_spi.c
> >>>>         drivers/spi/mxs_spi.c
> >>>>         drivers/spi/omap3_spi.c
> >>>>         drivers/spi/sh_qspi.c
> >>>>
> >>>> I'm looking for proper options along with removal of some legacy code,
> >>>> and tiny-dm.
> >>>
> >>> For the number of about to be year past published deadline (which has
> >>> been extended at times to get to that point even) boards, I think we
> >>> need to start by dropping boards.  Then we can see what makes sense
> >>> moving forward.
> >>
> >> At least mxc_spi and sh_qspi must stay, since those are heavily used in
> >> embedded/industrial/automotive.
> > 
> > So, this brings us back to the main topic of this thread.  Both of the
> > drivers you mention ARE converted to DM, but cannot fit adding DM to
> > SPL.  Where do we put non-DM SPL code as we have real size constraints
> > in SPL/TPL?  I should bring this up in Simon's new thread too, but I
> > wonder if we shouldn't just make drivers/spl/{mmc,spi,xxx}/ and have the
> > non-DM-framework drivers for SPL reside somewhere and move on.  The
> > notions of "we have a nice abstract framework" and "we need to be as
> > small as possible" can and do conflict.
> 
> But then how do you propose to keep sharing code between the two worlds?

Sharing defines is easy.  Sharing information buried in the device tree
requires some of the dtoc changes either in progress or variations on
them.  Sharing other functionality?  Depends on what fits well
(logically) in inline functions.  But I don't see some duplication of
either functional (i.e. read()/write()) nor initialization code as a
hard blocker.

But the only choice that doesn't have some duplication of code would be
"throw out current DM, replace with a new DM that's small enough in all
cases".  And we're at a few years now of "DM is too big and bloaty!"
without "here are my patches to slim down DM for all cases".

-- 
Tom
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