Re: [PATCH] Add new command fs2bridge for socfpga

[Steffen Trumtrar <s.trumtrar@pengutronix.de>]

Hi!

Andrey Smirnov <andrew.smirnov@gmail.com> writes:

> On Sun, Jul 30, 2017 at 2:17 PM, Mabcded Babcde
> <thepusherpushes@gmail.com> wrote:
>> 2017-07-28 15:42 GMT+02:00 Andrey Smirnov <andrew.smirnov@gmail.com>:
>>> On Fri, Jul 28, 2017 at 6:24 AM, Mabcded Babcde
>>> <thepusherpushes@gmail.com> wrote:
>>>> 2017-07-27 20:49 GMT+02:00 Andrey Smirnov <andrew.smirnov@gmail.com>:
>>>>> On Thu, Jul 27, 2017 at 9:20 AM, Mabcded Babcde
>>>>> <thepusherpushes@gmail.com> wrote:
>>>>>> Hi,
>>>>>> this patch adds a new command to barebox. It is used to enable or
>>>>>> disable the fpga-to-sdram bridges on socfpgas. The patch is based on a
>>>>>> manual from altera
>>>>>> (https://www.altera.com/support/support-resources/knowledge-base/embedded/2016/how-and-when-can-i-enable-the-fpga2sdram-bridge-on-cyclone-v-soc.html)
>>>>>> and a implementation for u-boot
>>>>>> (https://github.com/rogerq/u-boot/blob/master/arch/arm/mach-socfpga/misc.c).
>>>>>> The fpga2sdram fpga configuration can only be set when the SDRAM
>>>>>> interface is idle. So it is necessary to use the on-chip ram.
>>>>>
>>>>> And by "on-chip ram" you mean i-cache and not SRAM block used by first
>>>>> stage bootloader, correct? I am just a bit confused by the wording.
>>>>>
>>>>
>>>> Sorry, my fault. I meant i-cache.
>>>>
>>>>>> To bring all fpga2sdram bridges out of reset it is necessary to write 0x3FFF to
>>>>>> the register. Only the fpga2sdram bridges are enabled or disabled but
>>>>>> no other bridges like the axi bridges.
>>>>>
>>>>> Linux kernel already has:
>>>>>
>>>>> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/fpga/altera-fpga2sdram-bridge.txt?h=v4.13-rc2
>>>>>
>>>>> so, IMHO, it would be better to implement  a compatible driver and, if
>>>>> ability to change the value at run-time is needed, add "enable"
>>>>> property to it rather than introducing a separate command.
>>>>>
>>>>
>>>> But how can I ensure that the SDRAM is idle? I quote Altera:
>>>> "First time enabling of the FPGA2SDRAM bridge within Linux is not
>>>> supported as the SDRAM subsystem cannot be easily put into a
>>>> guaranteed idle state."
>>>>
>>>
>>> I feel like we are talking about different things. What I am trying to
>>> say that instead of adding this functionality to Barebox as a
>>> standalone command, it would be better to add it _to Barebox_ as a
>>> driver that claims compatibility with "altr,socfpga-fpga2sdram-bridge"
>>> and implements all of the necessary logic there. It would be the same
>>> code running in the boot-loader but triggered to executed via
>>> different means, so it should literally be the same in terms of SDRAM
>>> access quiescence. A somewhat relative example of that approach would
>>> be "drivers/firmware/socfpga.c".
>>
>> Ok, I hardcoded my code from the command to drivers/firmware/socfpga.c
>> for testing purposes. That didn't seem to work.
>
> I'd double check that CONFIG_FIRMWARE and
> CONFIG_FIRMWARE_ALTERA_SOCFPGA are set to "y".
>
>> However how would I
>> enable or disable the bridge? With a parameter? Where can I add it and
>> change it?
>>
>>>
>
> The driver in firmware/socfpga.c should create a "fpga0" device, after
> which, you cat set that device's variables/attributes by simply doing:
>
> fpga0.variable_name = value
>
> and get them via
>
> echo ${fpga0.variable_name}
>

The right approach should be adding a proper bridge driver like in the
kernel. Then in the fpgamgr_program_finish enable all registered
bridges. And set the APPFLYCFG bit in the bridge driver.
Or do I miss something?

The cacheline magic seems rather fragile and therefore just running a
function (with almost the same assembler code) from OCRAM seems to be the
more robust option.

As a matter of fact, I already have the bridge drivers ported to
barebox. I can post the series as an RFC as I haven't tested it since I
rebased it to v2017.07.0.


Regards,
Steffen

-- 
Pengutronix e.K.                           | Steffen Trumtrar            |
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