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

[Marek Vasut]

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.

>  > 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