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SubjectRE: [PATCH 5/5] misc: zynqmp: Add afi config driver
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Hi Greg,

Please find my response inline.

> -----Original Message-----
> From: Greg KH <gregkh@linuxfoundation.org>
> Sent: Tuesday, April 20, 2021 8:58 PM
> To: Nava kishore Manne <navam@xilinx.com>
> Cc: robh+dt@kernel.org; Michal Simek <michals@xilinx.com>; Derek Kiernan
> <dkiernan@xilinx.com>; Dragan Cvetic <draganc@xilinx.com>;
> arnd@arndb.de; Rajan Vaja <RAJANV@xilinx.com>; Jolly Shah
> <JOLLYS@xilinx.com>; Tejas Patel <tejasp@xlnx.xilinx.com>; Amit Sunil
> Dhamne <amitsuni@xilinx.com>; devicetree@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> chinnikishore369@gmail.com; git <git@xilinx.com>
> Subject: Re: [PATCH 5/5] misc: zynqmp: Add afi config driver
>
> On Tue, Apr 20, 2021 at 01:47:17PM +0000, Nava kishore Manne wrote:
> > Hi Greg,
> >
> > Please find my response inline.
> >
> > > -----Original Message-----
> > > From: Greg KH <gregkh@linuxfoundation.org>
> > > Sent: Tuesday, April 20, 2021 2:21 PM
> > > To: Nava kishore Manne <navam@xilinx.com>
> > > Cc: robh+dt@kernel.org; Michal Simek <michals@xilinx.com>; Derek
> > > Kiernan <dkiernan@xilinx.com>; Dragan Cvetic <draganc@xilinx.com>;
> > > arnd@arndb.de; Rajan Vaja <RAJANV@xilinx.com>; Jolly Shah
> > > <JOLLYS@xilinx.com>; Tejas Patel <tejasp@xlnx.xilinx.com>; Amit
> > > Sunil Dhamne <amitsuni@xilinx.com>; devicetree@vger.kernel.org;
> > > linux-arm- kernel@lists.infradead.org; linux-kernel@vger.kernel.org;
> > > chinnikishore369@gmail.com; git <git@xilinx.com>
> > > Subject: Re: [PATCH 5/5] misc: zynqmp: Add afi config driver
> > >
> > > On Tue, Apr 20, 2021 at 01:41:53PM +0530, Nava kishore Manne wrote:
> > > > This patch adds zynqmp afi config driver.This is useful for the
> > > > configuration of the PS-PL interface on Zynq US+ MPSoC platform.
> > > >
> > > > Signed-off-by: Nava kishore Manne <nava.manne@xilinx.com>
> > > > ---
> > > > drivers/misc/Kconfig | 11 ++++++
> > > > drivers/misc/Makefile | 1 +
> > > > drivers/misc/zynqmp-afi.c | 83
> > > > +++++++++++++++++++++++++++++++++++++++
> > > > 3 files changed, 95 insertions(+) create mode 100644
> > > > drivers/misc/zynqmp-afi.c
> > > >
> > > > diff --git a/drivers/misc/Kconfig b/drivers/misc/Kconfig index
> > > > 877b43b3377d..d1ea1eeb3ac1 100644
> > > > --- a/drivers/misc/Kconfig
> > > > +++ b/drivers/misc/Kconfig
> > > > @@ -456,6 +456,17 @@ config ZYNQ_AFI
> > > > between PS and PL, the AXI port data path should be configured
> > > > with the proper Bus-width values
> > > >
> > > > +config ZYNQMP_AFI
> > > > + tristate "Xilinx ZYNQMP AFI support"
> > > > + help
> > > > + ZynqMP AFI driver support for writing to the AFI registers for
> > > > + configuring PS_PL Bus-width. Xilinx Zynq US+ MPSoC connect the
> > > > + PS to the programmable logic (PL) through the AXI port. This AXI
> > > > + port helps to establish the data path between the PS and PL.
> > > > + In-order to establish the proper communication path between
> > > > + PS and PL, the AXI port data path should be configured with
> > > > + the proper Bus-width values
> > > > +
> > > > source "drivers/misc/c2port/Kconfig"
> > > > source "drivers/misc/eeprom/Kconfig"
> > > > source "drivers/misc/cb710/Kconfig"
> > > > diff --git a/drivers/misc/Makefile b/drivers/misc/Makefile index
> > > > e9b03843100f..54bd0edc511e 100644
> > > > --- a/drivers/misc/Makefile
> > > > +++ b/drivers/misc/Makefile
> > > > @@ -57,3 +57,4 @@ obj-$(CONFIG_UACCE) += uacce/
> > > > obj-$(CONFIG_XILINX_SDFEC) += xilinx_sdfec.o
> > > > obj-$(CONFIG_HISI_HIKEY_USB) += hisi_hikey_usb.o
> > > > obj-$(CONFIG_ZYNQ_AFI) += zynq-afi.o
> > > > +obj-$(CONFIG_ZYNQMP_AFI) += zynqmp-afi.o
> > > > diff --git a/drivers/misc/zynqmp-afi.c b/drivers/misc/zynqmp-afi.c
> > > > new file mode 100644 index 000000000000..a318652576d2
> > > > --- /dev/null
> > > > +++ b/drivers/misc/zynqmp-afi.c
> > > > @@ -0,0 +1,83 @@
> > > > +// SPDX-License-Identifier: GPL-2.0
> > > > +/*
> > > > + * Xilinx FPGA AFI bridge.
> > > > + * Copyright (c) 2018-2021 Xilinx Inc.
> > > > + */
> > > > +
> > > > +#include <linux/err.h>
> > > > +#include <linux/firmware/xlnx-zynqmp.h> #include <linux/io.h>
> > > > +#include <linux/module.h> #include <linux/of.h> #include
> > > > +<linux/platform_device.h> #include <linux/slab.h>
> > > > +
> > > > +/**
> > > > + * struct zynqmp_afi_fpga - AFI register description
> > > > + * @value: value to be written to the register
> > > > + * @regid: Register id for the register to be written */ struct
> > > > +zynqmp_afi_fpga {
> > > > + u32 value;
> > > > + u32 regid;
> > > > +};
> > > > +
> > > > +static int zynqmp_afi_fpga_probe(struct platform_device *pdev) {
> > > > + struct zynqmp_afi_fpga *zynqmp_afi_fpga;
> > > > + struct device_node *np = pdev->dev.of_node;
> > > > + int i, entries, ret;
> > > > + u32 reg, val;
> > > > +
> > > > + zynqmp_afi_fpga = devm_kzalloc(&pdev->dev,
> > > > + sizeof(*zynqmp_afi_fpga), GFP_KERNEL);
> > > > + if (!zynqmp_afi_fpga)
> > > > + return -ENOMEM;
> > > > + platform_set_drvdata(pdev, zynqmp_afi_fpga);
> > > > +
> > > > + entries = of_property_count_u32_elems(np, "config-afi");
> > > > + if (!entries || (entries % 2)) {
> > > > + dev_err(&pdev->dev, "Invalid number of registers\n");
> > > > + return -EINVAL;
> > > > + }
> > > > +
> > > > + for (i = 0; i < entries / 2; i++) {
> > > > + ret = of_property_read_u32_index(np, "config-afi", i * 2,
> > > &reg);
> > > > + if (ret) {
> > > > + dev_err(&pdev->dev, "failed to read register\n");
> > > > + return -EINVAL;
> > > > + }
> > > > + ret = of_property_read_u32_index(np, "config-afi", i * 2 + 1,
> > > > + &val);
> > > > + if (ret) {
> > > > + dev_err(&pdev->dev, "failed to read value\n");
> > > > + return -EINVAL;
> > > > + }
> > > > + ret = zynqmp_pm_afi(reg, val);
> > > > + if (ret < 0) {
> > > > + dev_err(&pdev->dev, "AFI register write error
> %d\n",
> > > > + ret);
> > > > + return ret;
> > > > + }
> > > > + }
> > > > + return 0;
> > > > +}
> > >
> > > Again, why does this have to be in the kernel? All it does is make
> > > a single call to the hardware based on some values read from the
> > > device tree. Can't you do this from userspace?
> > >
> > For every PL design has its own PS-PL configuration.
>
> What is a "PL design", and what is a "PS-PL configuration"? :)
>
> > This driver will be used by the overlay framework for configuring the
> interface after programming the FPGA and before probing the drivers that
> are present in the PL.
>
> Again, I have no idea what this means at all.
>
> And again, why does this have to be done in the kernel? All you are doing is
> sending some random values read in DT down to a hardware
> device. What requires a kernel driver for this?
>

The ZynqMP based processing system (PS) that contains ARM cores and Xilinx programmable logic (PL/FPGA) in a single device. The PS and PL can be tightly or loosely coupled using multiple interfaces and other signals.
This enables the designer to effectively integrate user-created hardware accelerators and other functions in the PL logic that are accessible to the processors and can also access memory resources in the PS.
https://www.xilinx.com/support/documentation/user_guides/ug1085-zynq-ultrascale-trm.pdf (Page No: 1085)

To Program/Re-Program the PL at runtime in Linux we have a an FPGA Manger Framework and this frame work uses DT-Overlays to programming the FPGA and probing the relevant PL drivers.
For more info please refer this link: https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/fpga/fpga-region.txt

Every Zynq/ZynqMP PL(FPGA) design has its own PS-PL configuration. So after programming the FPGA and before probing the relevant PL drivers these PS-PL configurations should be set.

Example DT-Overlay file to program the PL(FPGA) from Linux:
/dts-v1/;
/plugin/;
/ {
fragment@0 { /* fragment 0 contains Bitstream info */
target = <&fpga_full>;
overlay0: __overlay__ {
#address-cells = <2>;
#size-cells = <2>;
firmware-name = "Base_Zynq_MPSoC_wrapper.bit.bin";
resets = <&zynqmp_reset 116>;
};
};
fragment@1 { /* fragment 1 contains PS-PL configurations */
target = <&amba>;
overlay1: __overlay__ {
afi0: afi0 {
compatible = "xlnx,afi-fpga";
config-afi = < 0 0>, <1 0>, <2 0>, <3 0>, <4 0>, <5 0>, <6 0>, <7 0>, <8 0>, <9 0>, <10 0>, <11 0>, <12 0>, <13 0>, <14 0xa00>, <15 0x000>;
};
};
};
fragment@2 { /* Fragment 2 contains the relevant drivers for the IP's present in the FPGA design*/
target = <&amba>;
overlay2: __overlay__ {
axi_gpio_0: gpio@a0000000 {
#gpio-cells = <2>;
clock-names = "s_axi_aclk";
clocks = <&zynqmp_clk 71>;
compatible = "xlnx,xps-gpio-1.00.a";
gpio-controller ;
reg = <0x0 0xa0000000 0x0 0x1000>;
};
};
} ;
};

In-order to support the PL(FPGA) programming and to configure the interface between PS and PL using FPGA Manager. This Driver is needed in the kernel space.

@Moritz Fischer: Can you please let us know your thoughts on this.

Regards,
Navakishore.

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