am335x: memory configuration

[Yegor Yefremov]

Hi Jan,

On Thu, Oct 6, 2016 at 3:45 PM, Jan Remmet <J.Remmet at phytec.de> wrote:
> On Thu, Oct 06, 2016 at 11:08:07AM +0200, Yegor Yefremov wrote:
>> I've submitted a patch [1] to support our Baltos systems back in the
>> May. There was an issue with dynamically detecting RAM size as the
>> systems can have either 256MB or 512MB modules.
>>
>> So far u-boot was able to detect the RAM size dynamically. In order to
>> do so it uses following code in arch/arm/cpu/armv7/am33xx/emif4.c:
>>
>> int dram_init(void)
>> {
>>
>> #ifndef CONFIG_SKIP_LOWLEVEL_INIT
>>         sdram_init();
>> #endif
>>
>>         /* dram_init must store complete ramsize in gd->ram_size */
>>         gd->ram_size = get_ram_size(
>>                         (void *)CONFIG_SYS_SDRAM_BASE,
>>                         CONFIG_MAX_RAM_BANK_SIZE);
>>         return 0;
>> }
>>
>> void dram_init_banksize(void)
>> {
>>         gd->bd->bi_dram[0].start = CONFIG_SYS_SDRAM_BASE;
>>         gd->bd->bi_dram[0].size = gd->ram_size;
>> }
>>
>> This peace of code will be excuted in u-boot.img (not in MLO).
>>
>> In Barebox we have get_ram_size(), that provides real RAM size and
>> am335x_sdram_size(), that returns RAM controller settings. So far DDR
>> controler will be configured for 512MB regardless of the module. Hence
>> the return value from am335x_sdram_size() cannot be used for crating
>> ram0 node.
> On our am335x boards we use MLOs with individual RAM timings and EMIF config
> values. So am335x_sdram_size works fine in barebox.bin.
> Maybe get_ram_size works if the timing settings are equal?

I've solved the problem the way Sascha proposed earlier (see the third
version of my patch sent today).

In MLO I setup memory controller to 512MB, then I check the real
amount via  get_ram_size() and if I have 256MB I just reinitialize the
memory controller with values for 256Mb i.e. rows 14 instead of 15.
With this done one can use am335x_sdram_size() in other parts of
berebox.

Thanks for the feedback.

Yegor