Re: [PATCH 7/7] sunxi: H6: Enable SPI0 in DT when no eMMC is used

[Andre Przywara <andre.przywara@arm.com>]

On Thu, 24 Feb 2022 13:00:56 +0530
Jagan Teki <jagan@amarulasolutions.com> wrote:

Hi Jagan,

> On Thu, Jan 20, 2022 at 8:06 PM Jagan Teki <jagan@amarulasolutions.com> wrote:
> >
> > On Thu, Jan 20, 2022 at 7:36 PM Andre Przywara <andre.przywara@arm.com> wrote:  
> > >
> > > On Thu, 20 Jan 2022 19:08:57 +0530
> > > Jagan Teki <jagan@amarulasolutions.com> wrote:
> > >
> > > Hi,
> > >  
> > > > On Tue, Jan 11, 2022 at 6:16 PM Andre Przywara <andre.przywara@arm.com> wrote:  
> > > > >
> > > > > On the Allwinner H6 SoC both the SPI0 and the eMMC device share one pin,
> > > > > so cannot be used simultaneously. On Linux this is a showstopper, since
> > > > > only one of them would be able to claim the pin, and the probe order is
> > > > > somewhat random. The DT consequently disables SPI0 in favour of the more
> > > > > useful eMMC.
> > > > >
> > > > > But a comment in the DT actually suggests that this could be reversed by
> > > > > U-Boot, if no eMMC is actually connected. Let's now implement this:
> > > > > When we fix up the device tree before booting a kernel, we iterate over
> > > > > all MMC devices, and check if there is an eMMC device among them. If none
> > > > > can be found, we enable SPI0 instead, to allow Linux access to the SPI
> > > > > flash.  
> > > >  
> > > > > Since this fixup is not really universally applicable to all boards,
> > > > > let's hide it behind a Kconfig option, and enable it only on the one
> > > > > supported board where this makes sense: the Pine H64.
> > > > >
> > > > > Please note that the SPI functionality is still disabled in U-Boot
> > > > > proper, the pinmux clash affects us too: it would always disable the eMMC
> > > > > and so spoil this algorithm here.
> > > > >
> > > > > Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> > > > > ---
> > > > >  arch/arm/mach-sunxi/Kconfig | 10 ++++++++
> > > > >  board/sunxi/board.c         | 50 +++++++++++++++++++++++++++++++++++++
> > > > >  configs/pine_h64_defconfig  |  1 +
> > > > >  3 files changed, 61 insertions(+)
> > > > >
> > > > > diff --git a/arch/arm/mach-sunxi/Kconfig b/arch/arm/mach-sunxi/Kconfig
> > > > > index 56ff1e197c..ce66453029 100644
> > > > > --- a/arch/arm/mach-sunxi/Kconfig
> > > > > +++ b/arch/arm/mach-sunxi/Kconfig
> > > > > @@ -1047,6 +1047,16 @@ config BLUETOOTH_DT_DEVICE_FIXUP
> > > > >           The used address is "bdaddr" if set, and "ethaddr" with the LSB
> > > > >           flipped elsewise.
> > > > >
> > > > > +config SUNXI_H6_ENABLE_SPIFLASH
> > > > > +       bool "Enable H6 SPI flash vs. eMMC enablement"
> > > > > +       depends on MACH_SUN50I_H6
> > > > > +       default n
> > > > > +       help
> > > > > +         Enable this option if you want U-Boot check for an eMMC device
> > > > > +         on Allwinner H6 boards, and enable the SPI flash if none is found.
> > > > > +         SPI0 and MMC2 share one pin, so cannot coexist in Linux. The
> > > > > +         DT prefers eMMC, but if none is used, we can safely enable SPI.  
> > > >
> > > > Why we need a separate macro, cannot we check it H6 globally as it SoC design?  
> > >
> > > This "hack" is board dependent. We don't know if there is a SPI flash or
> > > eMMC in the first place, and this whole concept is weird enough that it
> > > warrants a separate config option.
> > > Probably due to this hardware issue the PineH64 is actually the only board
> > > in mainline that has both SPI flash and eMMC, and I don't want to enable
> > > SPI flash on every eMMC less board. Also it simplifies the code if we can
> > > assume that both DT nodes exist, when that config is enabled.
> > >
> > > Cheers,
> > > Andre
> > >
> > > P.S. Actually I wanted to forgot to mark this one as RFC, as I am not sure
> > > that it's justified. The comment in the mainline DT suggests this
> > > solution, and I was curious what it would take to make it work, as
> > > apparently some people are interested in it.  
> >
> > If it board-specific, better switch to RFC or load the overlay by
> > checking on board specific boot script.  
> 
> Anything about this?

Yeah, I meant to tag this patch as RFC (as I mentioned in the cover
letter), but the actually forgot to do it.
So overlays would be one solution - for kernels, at least, though not for
U-Boot. Is there some framework / functionality in place to automatically
apply them (outside of some user specific scripting)?

I will have a think about that, and will drop this patch for now.

Cheers,
Andre