On Wed, Jul 08, 2020 at 05:21:59PM +0200, Matthias Brugger wrote:

> Hi Tom,
> 
> I just realized that
> 88bd5b1793 ("configs: Resync with savedefconfig")
> 
> Delete the CONFIG_NR_DRAM_BANKS entries as added in this patch, which leads
> to a regression in RPi4 (only one GB of memory visible to the kernel if you
> use Grub for booting).
> 
> Is it generally wrong to add CONFIG_NR_DRAM_BANKS to the config files? What
> is the correct approach then?

So, if savedefconfig removes an entry from the file, it's not  needed.
In this case we see:
config NR_DRAM_BANKS
        int "Number of DRAM banks"
        default 1 if ARCH_SUNXI || ARCH_OWL
        default 4
        help
          This defines the number of DRAM banks.

In the top-level Kconfig file.  Since you set it as 4 and 4 is the
default, that's what's used:
$ make O=/tmp/rpi_4 rpi_4_config -sj
$ grep NR_D /tmp/rpi_4/.config
CONFIG_NR_DRAM_BANKS=4
$ grep ARCH_FIX /tmp/rpi_4/.config
CONFIG_ARCH_FIXUP_FDT_MEMORY=y

-- 
Tom

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