[U-Boot] arm: socfpga: Question about FPGA/HPS SDRAM Bridge

[Jian Luo]

Hi Marek,

On 02.09.2015 12:27, Marek Vasut wrote:
 > On Tuesday, September 01, 2015 at 02:32:26 PM, Jian Luo wrote:
 >> Hi Marek,
 >
 > Hi!
 >
 >> On 01.09.2015 14:03, Marek Vasut wrote:
 >>  > On Tuesday, September 01, 2015 at 01:49:43 PM, Jian Luo wrote:
 >> ----snip----
 >>
 >>  >> What about calling socfpga_sdram_apply_static_cfg() direct in
 >>  >> socfpga_load() in drivers/fpga/socfpga.c to make it generic?
 >>  >
 >>  > Which code exactly do you refer to ?
 >>
 >> I mean something like this.
 >>
 >> diff --git a/drivers/fpga/socfpga.c b/drivers/fpga/socfpga.c
 >> index 4448250..d0f67f6 100644
 >> --- a/drivers/fpga/socfpga.c
 >> +++ b/drivers/fpga/socfpga.c
 >> @@ -300,5 +300,12 @@ int socfpga_load(Altera_desc *desc, const void
 >> *rbf_data, size_t rbf_size)
 >>                  return status;
 >>
 >>          /* Ensure the FPGA entering user mode */
 >> -       return fpgamgr_program_poll_usermode();
 >> +       status = fpgamgr_program_poll_usermode();
 >> +       if (status)
 >> +               return status;
 >> +
 >> +       /* Latch FPGA2SDRAM bridge configuration */
 >> +       socfpga_sdram_apply_static_cfg();
 >> +
 >> +       return 0;
 >>   }
 >>
 >>  >> socfpga_load() already did step 1 and 2.
 >>  >> Is there any side effect  when fpga2sdram bridge is not used?
 >>  >
 >>  > The idea is to keep the FPGA programming code and the code which
 >>  > controls the bridges separate. The reason for that is that you 
can have
 >>  > content in the FPGA which is running completely independent of 
the HPS
 >>  > software. You don't always need to enable the bridges.
 >>
 >> No, it's the other way around here.
 >> socfpga_load() runs eventually when command "fpga load" is called.
 >> So when I explicitly use "fpga load" command, the old FPGA program is
 >> expected to stop running, right?
 >
 > Right
 >
 >> And I don't want to enable the bridge here, just to latch the SDRAM
 >> configuration.
 >
 > So what you want to do is "bridge disable ; fpga load ... ; bridge 
enable",
 > isn't that the correct sequence ? I might be missing something 
though, sorry.

No, you are right. Sorry, I didn't think it through.

My original thought was, that "fpga load" should not depend on "bridge e/d"
regardless of how fpga2sdram is configured. Now I think the dependency 
is a bad idea.
Sorry for the confusion.

 >
 >>  > The FPGA2SDRAM bridge (or, more like fpga2hps bridge) is used for 
stuff
 >>  > like framebuffers implemented in the FPGA, so that the FPGA can fetch
 >>  > data from the SDRAM.
 >>  >
 >>  > Best regards,
 >>  > Marek Vasut
 >>
 >> Best regards,
 >>
 >> Jian Luo
 >
 > Best regards,
 > Marek Vasut

Best regards,

Jian Luo