Re: [PATCH v12 3/6] fpga: add simple-fpga-bus

From: Moritz Fischer
Date: Wed Oct 28 2015 - 12:28:19 EST

On Wed, Oct 28, 2015 at 9:18 AM, Josh Cartwright <joshc@xxxxxx> wrote:
> On Wed, Oct 28, 2015 at 08:37:51AM -0700, Moritz Fischer wrote:
>> On Wed, Oct 28, 2015 at 3:07 AM, Josh Cartwright <joshc@xxxxxx> wrote:
>> > On Tue, Oct 27, 2015 at 05:09:12PM -0500, atull@xxxxxxxxxxxxxxxxxxxxx wrote:
>> >> From: Alan Tull <atull@xxxxxxxxxxxxxxxxxxxxx>
>> >>
>> >> The Simple FPGA bus uses the FPGA Manager Framework and the
>> >> FPGA Bridge Framework to provide a manufactorer-agnostic
>> >> interface for reprogramming FPGAs that is Device Tree
>> >> Overlays-based.
>> >
>> > Do you intend the "simple-fpga-bus" to be used on Zynq as well? The
>> > whole concept of the socfpga's "FPGA Bridge" doesn't map to the Zynq at
>> > all, from what I can tell.
>> For Zynq the zynq-fpga driver takes care of the level shifters on full
>> reconfiguration,
>> and doesn't for partial reconfiguration. Now depending on which parts
>> of the fabric
>> are partial reconfigured (say AXI masters), one might run into issues
>> with a setup like that.
>> My first plan was to counter that by using zynq-reset to hold the
>> reset high during
>> reconfiguration of that part of the FPGA.
>> I'm happy to rethink that part and maybe redo the level shifters and
>> resets together in a bridge
>> driver under devicetree control gives finer grained control.
> There is already a framework which is used to describe and manipulate
> level shifting/other IO properties, and that is pinctrl, and if we
> wanted to use an appropriate abstraction, I think pinctrl would be the
> best bet.

Alright, I'll investigate that. Again, for the non-partial reconfig
case I'm happy
with the behavior as implemented, for the partial reconfig I just
haven't run into
issues with not dealing with the level shifters.

> Implementing the FPGA Bridge interface in the Zynq driver because it's
> what the core expects is just backwards. It's an abstraction inversion.

Yeah, you're probably right.


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