Re: [PATCH 2/2] fpga: reset bridge: Add the reset bridge

From: Shubhrajyoti Datta <shubhrajyoti.datta@gmail.com>
To: Alan Tull <atull@kernel.org>
Cc: Moritz Fischer <mdf@kernel.org>,
	linux-fpga@vger.kernel.org, Rob Herring <robh+dt@kernel.org>,
	Michal Simek <michal.simek@xilinx.com>,
	"open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS"
	<devicetree@vger.kernel.org>,
	nofooter@xilinx.com,
	Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
Subject: Re: [PATCH 2/2] fpga: reset bridge: Add the reset bridge
Date: Thu, 1 Mar 2018 16:19:48 +0530	[thread overview]
Message-ID: <CAKfKVtE5u7z_ASmw_f6t6MAybAnoPm+rKm5LQZ_MaYmUEYuOhg@mail.gmail.com> (raw)
In-Reply-To: <CANk1AXR6aSwyQTW=NeYrRUQo2Oe8BysyOzf6VHvBuXaxKwNp-g@mail.gmail.com>

On Tue, Feb 27, 2018 at 10:30 PM, Alan Tull <atull@kernel.org> wrote:
> On Mon, Feb 26, 2018 at 10:46 PM, Shubhrajyoti Datta
> <shubhrajyoti.datta@gmail.com> wrote:
>> Hi  Moritz,
>>
>> On Tue, Feb 27, 2018 at 5:58 AM, Moritz Fischer <mdf@kernel.org> wrote:
>>> Hi Shubhrajyoti, Alan
>>>
>>> On Mon, Feb 26, 2018 at 04:53:59PM -0600, Alan Tull wrote:
>>>> On Tue, Feb 20, 2018 at 10:53 PM,  <shubhrajyoti.datta@gmail.com> wrote:
>>>> > From: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
>>>> >
>>>> > Adds the reset bridge. After the bitstream load the reset
>>>> > bridge helps in reseting the programable logic. The
>>>> > reset lines depends on the design.
>>>>
>>>> Hi Shubhrajyoti,
>>>>
>>>> OK so adding this 'bridge' will get a reset line to be toggled after
>>>> programming is done.  It looks like it might be generally usable.
>>>> This doesn't look very xilinx specific (i.e. no specific device
>>>> registers, just using a reset), so maybe it is just a 'rst-brige'.
>>>> How is it used?  To hit a reset line on a whole FPGA?
>>>
>>> In zynq-fpga we have the fpga-mgr hit on the reset, which to some
>>> extend I suppose makes sense, since after reload you wanna reset the
>>> entire FPGA space (unless you do PR, where you don't hit on the resets).
>>>
>>> Shubhrajyoti's solution seems more modular I guess, however I don't
>>> really see a good usecase for only hitting a single reset.
>>>
>>> IP that's in the FPGA and needs reset should have their dedicated resets
>>> via normal reset API bindings imho and not rely on bridges to do the
>>> right thing.
>>>
>>> The ZynqMP is fairly complex and I might be missing something here,
>>> so maybe you (Shubhrajyoti) can elaborate a bit more. The paragraph in
>>> the TRM seemed fairly short, and didn't enlighten me as to why it is
>>> required.
>>
>> The FPGA supports both the PR case and independent execution
>> Like  a design can have 2 parts that can have independent execution.
>
> I want to understand you better here.  What do you mean by
> 'independent execution'?  Like 2 partial reconfiguration regions that
> each have a single reset to reset the hardware in their region?  Or
> something else?
Yes.

>
>> In that case they have to have independent resets.
>>
>> There are 4 PS-PL lines that could be used by designs.
>> So in that case we should have  multiple resets.
>
> Normally, as Moritz is saying, the reset would be handled by the
> driver for the fabric-based hardware.
I didnt understand you mean the  platform-fpga.c ?

>
> Alan
>
>>
>>
>>>
>>> Cheers,
>>>
>>> Moritz
>>>>
>>>> Alan
>>>>
>>>> >
>>>> > Signed-off-by: Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>
>>>> > ---
>>>> >  drivers/fpga/Kconfig             |   8 ++++
>>>> >  drivers/fpga/Makefile            |   1 +
>>>> >  drivers/fpga/xilinx-rst-bridge.c | 100 +++++++++++++++++++++++++++++++++++++++
>>>> >  3 files changed, 109 insertions(+)
>>>> >  create mode 100644 drivers/fpga/xilinx-rst-bridge.c
>>>> >
>>>> > diff --git a/drivers/fpga/Kconfig b/drivers/fpga/Kconfig
>>>> > index ad5448f..752a907 100644
>>>> > --- a/drivers/fpga/Kconfig
>>>> > +++ b/drivers/fpga/Kconfig
>>>> > @@ -117,4 +117,12 @@ config XILINX_PR_DECOUPLER
>>>> >           region of the FPGA from the busses while that region is
>>>> >           being reprogrammed during partial reconfig.
>>>> >
>>>> > +config XILINX_RST_BRIDGE
>>>> > +       tristate "Xilinx Reset bridge"
>>>> > +       depends on FPGA_BRIDGE
>>>> > +       help
>>>> > +         Say Y to enable drivers for Xilinx Reset bridge.
>>>> > +         After writing the bitstream there has to be a reset.
>>>> > +         The reset lines are design specific.
>>>> > +
>>>> >  endif # FPGA
>>>> > diff --git a/drivers/fpga/Makefile b/drivers/fpga/Makefile
>>>> > index f98dcf1..c1b0d13 100644
>>>> > --- a/drivers/fpga/Makefile
>>>> > +++ b/drivers/fpga/Makefile
>>>> > @@ -23,6 +23,7 @@ obj-$(CONFIG_FPGA_BRIDGE)             += fpga-bridge.o
>>>> >  obj-$(CONFIG_SOCFPGA_FPGA_BRIDGE)      += altera-hps2fpga.o altera-fpga2sdram.o
>>>> >  obj-$(CONFIG_ALTERA_FREEZE_BRIDGE)     += altera-freeze-bridge.o
>>>> >  obj-$(CONFIG_XILINX_PR_DECOUPLER)      += xilinx-pr-decoupler.o
>>>> > +obj-$(CONFIG_FPGA_MGR_ZYNQMP_FPGA)     += xilinx-rst-bridge.o
>>>> >
>>>> >  # High Level Interfaces
>>>> >  obj-$(CONFIG_FPGA_REGION)              += fpga-region.o
>>>> > diff --git a/drivers/fpga/xilinx-rst-bridge.c b/drivers/fpga/xilinx-rst-bridge.c
>>>> > new file mode 100644
>>>> > index 0000000..8062283
>>>> > --- /dev/null
>>>> > +++ b/drivers/fpga/xilinx-rst-bridge.c
>>>> > @@ -0,0 +1,100 @@
>>>> > +// SPDX-License-Identifier: GPL-2.0
>>>> > +/*
>>>> > + * Xilinx FPGA reset bridge.
>>>> > + * Copyright (c) 2018 Xilinx Inc.
>>>> > + *
>>>> > + */
>>>> > +
>>>> > +#include <linux/kernel.h>
>>>> > +#include <linux/module.h>
>>>> > +#include <linux/of_device.h>
>>>> > +#include <linux/fpga/fpga-bridge.h>
>>>> > +#include <linux/reset.h>
>>>> > +
>>>> > +struct xlnx_rst_bridge_priv {
>>>> > +       struct device *dev;
>>>> > +       bool enable;
>>>> > +};
>>>> > +
>>>> > +static int xlnx_rst_bridge_enable_set(struct fpga_bridge *bridge, bool enable)
>>>> > +{
>>>> > +       struct xlnx_rst_bridge_priv *priv = bridge->priv;
>>>> > +       struct device *dev = priv->dev;
>>>> > +       struct reset_control *rstc;
>>>> > +       int ret = 0;
>>>> > +
>>>> > +       if (enable) {
>>>> > +               rstc = of_reset_control_array_get(dev->of_node, false, false);
>>>> > +               if (IS_ERR(rstc))
>>>> > +                       return PTR_ERR(rstc);
>>>> > +
>>>> > +               ret = reset_control_reset(rstc);
>>>> > +
>>>> > +               reset_control_put(rstc);
>>>> > +
>>>> > +               if (ret)
>>>> > +                       dev_err(dev, "Reset failed\n");
>>>> > +       } else {
>>>> > +               dev_dbg(dev, "Bridge disabled\n");
>>>> > +       }
>>>> > +
>>>> > +       if (!ret)
>>>> > +               priv->enable = enable;
>>>> > +
>>>> > +       return ret;
>>>> > +}
>>>> > +
>>>> > +static int xlnx_rst_bridge_enable_show(struct fpga_bridge *bridge)
>>>> > +{
>>>> > +       struct xlnx_rst_bridge_priv *priv = bridge->priv;
>>>> > +
>>>> > +       return priv->enable;
>>>> > +}
>>>> > +
>>>> > +static struct fpga_bridge_ops xlnx_rst_bridge_ops = {
>>>> > +       .enable_set = xlnx_rst_bridge_enable_set,
>>>> > +       .enable_show = xlnx_rst_bridge_enable_show,
>>>> > +};
>>>> > +
>>>> > +static int xlnx_rst_bridge_probe(struct platform_device *pdev)
>>>> > +{
>>>> > +       struct xlnx_rst_bridge_priv *priv;
>>>> > +       struct device *dev = &pdev->dev;
>>>> > +
>>>> > +       priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
>>>> > +       if (!priv)
>>>> > +               return -ENOMEM;
>>>> > +
>>>> > +       priv->dev = dev;
>>>> > +
>>>> > +       return fpga_bridge_register(dev, "xlnx_rst_bridge",
>>>> > +                                   &xlnx_rst_bridge_ops, priv);
>>>> > +}
>>>> > +
>>>> > +static int xlnx_rst_bridge_remove(struct platform_device *pdev)
>>>> > +{
>>>> > +       fpga_bridge_unregister(&pdev->dev);
>>>> > +
>>>> > +       return 0;
>>>> > +}
>>>> > +
>>>> > +static const struct of_device_id xlnx_rst_bridge_of_match[] = {
>>>> > +       { .compatible = "xlnx,rst-bridge", },
>>>> > +       {},
>>>> > +};
>>>> > +MODULE_DEVICE_TABLE(of, xlnx_rst_bridge_of_match);
>>>> > +
>>>> > +static struct platform_driver xlnx_rst_bridge_driver = {
>>>> > +       .probe = xlnx_rst_bridge_probe,
>>>> > +       .remove = xlnx_rst_bridge_remove,
>>>> > +       .driver = {
>>>> > +               .name   = "xlnx_rst_bridge",
>>>> > +               .of_match_table = of_match_ptr(xlnx_rst_bridge_of_match),
>>>> > +       },
>>>> > +};
>>>> > +
>>>> > +module_platform_driver(xlnx_rst_bridge_driver);
>>>> > +
>>>> > +MODULE_DESCRIPTION("Xilinx reset Bridge");
>>>> > +MODULE_AUTHOR("Shubhrajyoti Datta <shubhrajyoti.datta@xilinx.com>");
>>>> > +MODULE_LICENSE("GPL v2");
>>>> > --
>>>> > 2.1.1
>>>> >
>>>> > --
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