[U-Boot] [PATCH 1/4] lib: fdtdec: Fill initial ram top with DDR start value from dt

[Siva Durga Prasad Paladugu]

Hi Simon,

> -----Original Message-----
> From: sjg at google.com [mailto:sjg at google.com] On Behalf Of Simon Glass
> Sent: Saturday, June 09, 2018 3:29 AM
> To: Michal Simek <michal.simek at xilinx.com>
> Cc: Siva Durga Prasad Paladugu <sivadur at xilinx.com>; U-Boot Mailing List
> <u-boot at lists.denx.de>; Tom Rini <trini at konsulko.com>
> Subject: Re: [PATCH 1/4] lib: fdtdec: Fill initial ram top with DDR start value
> from dt
> 
> Hi,
> 
> 
> On 7 June 2018 at 06:18, Michal Simek <michal.simek at xilinx.com> wrote:
> > Hi,
> >
> > On 5.6.2018 09:20, Siva Durga Prasad Paladugu wrote:
> >> Fill initial ram top with DDR base addr value from DT as not filling
> >> it here always assumes it as zero while calculating relocation offset
> >> and hence lead to failures in somecases. This will assumed as zero if
> >> CONFIG_SYS_SDRAM_BASE is not defined.
> >>
> >> Signed-off-by: Siva Durga Prasad Paladugu
> >> <siva.durga.paladugu at xilinx.com>
> >> Signed-off-by: Michal Simek <michal.simek at xilinx.com>
> >> ---
> >>  lib/fdtdec.c | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/lib/fdtdec.c b/lib/fdtdec.c index f4e8dbf..34ef9b8
> >> 100644
> >> --- a/lib/fdtdec.c
> >> +++ b/lib/fdtdec.c
> >> @@ -1172,6 +1172,7 @@ int fdtdec_setup_memory_size(void)
> >>       }
> >>
> >>       gd->ram_size = (phys_size_t)(res.end - res.start + 1);
> >> +     gd->ram_top = (unsigned long)res.start;
> >>       debug("%s: Initial DRAM size %llx\n", __func__,
> >>             (unsigned long long)gd->ram_size);
> >>
> >>
> >
> > I am curious about ram_top meaning. It is used more as ram_base.
> >
> > I expect we can workaround it by board_get_usable_ram_top() where we
> > decode it exactly the same as patched fdtdec_setup_memory_size() but I
> > don't think it is better solution than this one.
> >
> > Simon/Tom: any comment?
> 
> I wonder why it is not set to res.end in this patch?
> 
> Comments from global_data.h:
> 
> unsigned long ram_top; /* Top address of RAM used by U-Boot */
> phys_size_t ram_size; /* RAM size */

Yes, it holds the ram high address but, initially it should contain start address then in routine setup_dest_addr() (file common_board_f.c), it will be updated by getting the
total mem size as below.
gd->ram_top += get_effective_memsize();

Lets consider if start address is non zero then it results in wrong ram_top without this patch. So, this patch fixes it by initializing it to ram start address and later in setup_dest_addr(), it will be updated to actual ram high address.
Otherway of fixing it is, we should add new variable to gd_t to hold ram_start and then while calculating ram_top in setup_dest_addr(), we should use it as gd->ram_top = gd->ram_start + get_effective_memsize() as
gd->bd->bi_dram[0].start didn’t get filled by this time during init. 


Thanks,
Siva
> 
> Regards,
> Simon