[U-Boot] [PATCH v1 1/4] arm: socfpga: imply SPL config instead of select

[Tom Rini]

On Mon, Jan 14, 2019 at 10:30:36PM +0100, Marek Vasut wrote:
> On 1/14/19 10:28 PM, Tom Rini wrote:
> > On Mon, Jan 14, 2019 at 07:31:26PM +0100, Marek Vasut wrote:
> >> On 1/14/19 5:05 PM, Simon Goldschmidt wrote:
> >>> Hi Dinh,
> >>
> >> Hi,
> >>
> >>> Am 14.01.2019 um 16:58 schrieb Dinh Nguyen:
> >>>> Hi Simon,
> >>>>
> >>>> On 1/14/19 9:50 AM, Simon Goldschmidt wrote:
> >>>>> Am 11.01.2019 um 23:02 schrieb Marek Vasut:
> >>>>>> On 1/11/19 9:39 PM, Simon Goldschmidt wrote:
> >>>>>>> Am 07.01.2019 um 23:53 schrieb Marek Vasut:
> >>>>>>>> On 1/7/19 10:14 PM, Simon Goldschmidt wrote:
> >>>>>>>>> In order to build a smaller SPL, let's imply SPL_DM_RESET and
> >>>>>>>>> SPL_WATCHDOG_SUPPORT instead of selecting them, so they can be
> >>>>>>>>> disabled
> >>>>>>>>> via defconfig.
> >>>>>>>>>
> >>>>>>>>> This also seems to be required to use OF_PLATDATA, as the reset
> >>>>>>>>> drivers
> >>>>>>>>> don't seem to work with it.
> >>>>>>>>
> >>>>>>>> How do you un-reset IP blocks if you disable the reset controller ?
> >>>>>>>
> >>>>>>> I found that out just now: there's the function
> >>>>>>> 'reset_deassert_peripherals_handoff()' in spl_gen5.c that should
> >>>>>>> "De-assert reset for peripherals and bridges based on handoff".
> >>>>>>> However,
> >>>>>>> at least for Gen5, it just writes a 0 to rstmgr->permodrst. By doing
> >>>>>>> that, it enables *ALL* peripherals on the SoC (except for some DMA
> >>>>>>> channels that aren't really used) :-)
> >>>>>>>
> >>>>>>> I guess that needs some cleaning up as well ;-)
> >>>>>>
> >>>>>> Yes
> >>>>>>
> >>>>>>> I think the proper thing to do here would be to remove this
> >>>>>>> function and
> >>>>>>> convert all drivers to provide appropriate 'resets' properties in the
> >>>>>>> dts?
> >>>>>>
> >>>>>> Indeed
> >>>>>
> >>>>> So I just did that and it works nice for SPL and U-Boot: By adding some
> >>>>> "resets" properties the the main dtsi and adding reset bulk code to the
> >>>>> cadence_qspi, denali_dt nand and drivers, I can nearly remove the reset
> >>>>> code from arch/mach_socfpga.
> >>>>>
> >>>>> The problem would be that now Linux cannot use peripherals that aren't
> >>>>> enabled by U-Boot because it relies on them being enabled. How are such
> >>>>> dependencies solved? Because even if I would add reset support in the
> >>>>> corresponding Linux drivers, we probably could not bootolder Kernels
> >>>>> (e.g. the Debian 9 kernel - v4.9.x) with a new U-Boot...
> >>>>>
> >>>>
> >>>> I added an early reset driver for SoCFPGA that should take care of this.
> >>>> The patch is in v5.0-rc2[1].
> >>>
> >>> OK, it's good to know that this work is already done, I haven't
> >>> monitored this close enough.
> >>
> >> We had the same problem with A10, indeed.
> >>
> >>> But am I correct that my above problem remains even in v5.0 as not all
> >>> peripherals in socfpga.dtsi have a "resets" property set (e.g. mmc and
> >>> qspi) and would thuse not be taken out of reset by Linux?
> >>>
> >>> Plus: should U-Boot work with older Linux kernels? Because if so, we
> >>> need fallback code in U-Boot to unreset peripherals when running with an
> >>> older kernel...
> >>
> >> Yes, it'd break old broken kernels . The real question is, do we care ?
> > 
> > Yes, we care.  Especially since it sounds like we're talking about
> > something that's an LTS and not super-ancient vendor kernel.  Off the
> > top of my head I can't recall if we ever fully removed support in sunxi
> > for the vendor kernel in some cases, or just made it, eventually, opt-in
> > as it was a fairly annoying incompatible behavior case.
> > 
> > But yes, in general, we do care about old kernels and need to be loud
> > and clear about when we're removing support for them on a given SoC due
> > to it being a PITA to support both ways of doing X and people have had Y
> > years to migrate or correct their kernel.
> 
> Then we have to add some fallback mechanism, possibly the env variable
> to tell reset controller to unreset everything.

Alright, so the prior art in question is:
commit accc9e446be6c3bd129315a0c5830bddccfa16da
Author: Hans de Goede <hdegoede at redhat.com>
Date:   Wed Oct 22 14:56:36 2014 +0200

    sunxi: Add CONFIG_OLD_SUNXI_KERNEL_COMPAT Kconfig option

And is about supporting the sunxi 3.4 vendor kernel tree, and something
we have still (and a single enabler of).  So, what's the range of broken
/ not broken kernels here?

-- 
Tom
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