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

[Simon Goldschmidt <simon.k.r.goldschmidt@gmail.com>]

Hi Dinh,

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.

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...

Regards,
Simon

> 
> Dinh
> 
> [1]
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/reset?id=b3ca9888f35fa6919569cf27c929dc0ac49e9716
>