RE: [PATCH 2/2] fpga: zynq: Add AFI config driver

[Nava kishore Manne]

Hi Mortiz,

Thanks for proving the comments.
Please find my response inline.

> -----Original Message-----
> From: Moritz Fischer [mailto:mdf@xxxxxxxxxx]
> Sent: Thursday, April 23, 2020 8:59 AM
> To: Nava kishore Manne <navam@xxxxxxxxxx>
> Cc: mdf@xxxxxxxxxx; Michal Simek <michals@xxxxxxxxxx>; linux-
> fpga@xxxxxxxxxxxxxxx; linux-arm-kernel@xxxxxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; chinnikishore369@xxxxxxxxx
> Subject: Re: [PATCH 2/2] fpga: zynq: Add AFI config driver
> 
> Hi Nava,
> 
> On Wed, Apr 15, 2020 at 03:54:50PM +0530, Nava kishore Manne wrote:
> > This patch Adds AFI config driver. This is useful for the PS to PL
> > configuration for the fpga manager On zynq platform.
> >
> > Signed-off-by: Nava kishore Manne <nava.manne@xxxxxxxxxx>
> > ---
> >  drivers/fpga/Kconfig    |  8 +++++
> >  drivers/fpga/Makefile   |  1 +
> >  drivers/fpga/zynq-afi.c | 81
> > +++++++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 90 insertions(+)
> >  create mode 100644 drivers/fpga/zynq-afi.c
> >
> > diff --git a/drivers/fpga/Kconfig b/drivers/fpga/Kconfig index
> > 474f304e..60982a0 100644
> > --- a/drivers/fpga/Kconfig
> > +++ b/drivers/fpga/Kconfig
> > @@ -214,4 +214,12 @@ config FPGA_MGR_ZYNQMP_FPGA
> >  	  to configure the programmable logic(PL) through PS
> >  	  on ZynqMP SoC.
> >
> > +config FPGA_MGR_ZYNQ_AFI_FPGA
> > +	bool "Xilinx AFI FPGA"
> > +	depends on FPGA_MGR_ZYNQ_FPGA
> Curious. How does this dependency play in here?
> > +	help
> > +	  Zynq AFI driver support for writing to the AFI registers
> > +	  for configuring the PS_PL interface. For some of the bitstream
> > +	  or designs to work the PS to PL interfaces need to be configured
> > +	  like the data bus-width etc.
> >  endif # FPGA
> > diff --git a/drivers/fpga/Makefile b/drivers/fpga/Makefile index
> > 312b937..d115e29 100644
> > --- a/drivers/fpga/Makefile
> > +++ b/drivers/fpga/Makefile
> > @@ -26,6 +26,7 @@ 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-$(CONFIG_FPGA_MGR_ZYNQ_AFI_FPGA)	+= zynq-afi.o
> >
> >  # High Level Interfaces
> >  obj-$(CONFIG_FPGA_REGION)		+= fpga-region.o
> > diff --git a/drivers/fpga/zynq-afi.c b/drivers/fpga/zynq-afi.c new
> > file mode 100644 index 0000000..7ce0d08
> > --- /dev/null
> > +++ b/drivers/fpga/zynq-afi.c
> > @@ -0,0 +1,81 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Xilinx FPGA AFI driver.
> > + * Copyright (c) 2018 Xilinx Inc.
> > + */
> > +
> > +#include <linux/err.h>
> > +#include <linux/io.h>
> > +#include <linux/module.h>
> > +#include <linux/of.h>
> > +#include <linux/platform_device.h>
> > +
> > +/* Registers and special values for doing register-based operations */
> > +#define AFI_RDCHAN_CTRL_OFFSET	0x00
> > +#define AFI_WRCHAN_CTRL_OFFSET	0x14
> > +
> > +#define AFI_BUSWIDTH_MASK	0x01
> > +
> > +/**
> > + * struct afi_fpga - AFI register description
> > + * @membase:	pointer to register struct
> > + * @afi_width:	AFI bus width to be written
> > + */
> > +struct zynq_afi_fpga {
> > +	void __iomem	*membase;
> > +	u32		afi_width;
> > +};
> > +
> > +static int zynq_afi_fpga_probe(struct platform_device *pdev) {
> > +	struct zynq_afi_fpga *afi_fpga;
> > +	struct resource *res;
> > +	u32 reg_val;
> > +	u32 val;
> > +
> > +	afi_fpga = devm_kzalloc(&pdev->dev, sizeof(*afi_fpga), GFP_KERNEL);
> > +	if (!afi_fpga)
> > +		return -ENOMEM;
> > +
> > +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > +	afi_fpga->membase = devm_ioremap_resource(&pdev->dev, res);
> > +	if (IS_ERR(afi_fpga->membase))
> > +		return PTR_ERR(afi_fpga->membase);
> > +
> > +	val = device_property_read_u32(&pdev->dev, "xlnx,afi-width",
> > +				       &afi_fpga->afi_width);
> > +	if (val) {
> > +		dev_err(&pdev->dev, "Fail to get the afi bus width\n");
> > +		return -EINVAL;
> > +	}
> > +
> > +	reg_val = readl(afi_fpga->membase + AFI_RDCHAN_CTRL_OFFSET);
> > +	reg_val &= ~AFI_BUSWIDTH_MASK;
> > +	writel(reg_val | afi_fpga->afi_width,
> > +	       afi_fpga->membase + AFI_RDCHAN_CTRL_OFFSET);
> > +	reg_val = readl(afi_fpga->membase + AFI_WRCHAN_CTRL_OFFSET);
> > +	reg_val &= ~AFI_BUSWIDTH_MASK;
> > +	writel(reg_val | afi_fpga->afi_width,
> > +	       afi_fpga->membase + AFI_WRCHAN_CTRL_OFFSET);
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct of_device_id zynq_afi_fpga_ids[] = {
> > +	{ .compatible = "xlnx,zynq-afi-fpga" },
> > +	{ },
> > +};
> > +MODULE_DEVICE_TABLE(of, zynq_afi_fpga_ids);
> > +
> > +static struct platform_driver zynq_afi_fpga_driver = {
> > +	.driver = {
> > +		.name = "zynq-afi-fpga",
> > +		.of_match_table = zynq_afi_fpga_ids,
> > +	},
> > +	.probe = zynq_afi_fpga_probe,
> > +};
> > +module_platform_driver(zynq_afi_fpga_driver);
> > +
> > +MODULE_DESCRIPTION("ZYNQ FPGA AFI module");
> MODULE_AUTHOR("Nava
> > +kishore Manne <nava.manne@xxxxxxxxxx>"); MODULE_LICENSE("GPL v2");
> > --
> > 2.7.4
> >
> 
> It looks like all the driver does is writing two registers? How does
> that fit into FPGA Manager as a framework. Should this maybe be eithe
> for Zynq architecture or a Misc driver instead?
> 
To establish the proper communication channel between PS and PL, The AXI Interface Bus Width should be configured properly.
For a design to design this AXI Interface Bus Width settings are vary. So for Zynq just loading the Bitstream into the PL is not sufficient
to establish a proper communication channel between PS and PL we have to do AXI Interface Bus Width settings as per the design
after loading the Bit file into the PL. I feel this is more relevant to the FPGA settings so I have placed this driver here.

Please suggest the best place to put this driver.

> Is the idea here to create the device via an overlay?
Yes, this driver loading/removal is triggered by the overlay after loading the bit file into the PL.

Regards,
Navakishore.