Adding a DFL (Device Feature List) device driver of ToD device for
Intel FPGA cards.

The Intel FPGA Time of Day(ToD) IP within the FPGA DFL bus is exposed
as PTP Hardware clock(PHC) device to the Linux PTP stack to synchronize
the system clock to its ToD information using phc2sys utility of the
Linux PTP stack. The DFL is a hardware List within FPGA, which defines
a linked list of feature headers within the device MMIO space to provide
an extensible way of adding subdevice features.

Signed-off-by: Raghavendra Khadatare <redacted>
Signed-off-by: Tianfei Zhang <redacted>

---
v2:
- handle NULL for ptp_clock_register().
- use readl_poll_timeout_atomic() instead of readl_poll_timeout(), and
  change the interval timeout to 10us.
- fix the uninitialized variable.
---
 MAINTAINERS               |   7 +
 drivers/ptp/Kconfig       |  13 ++
 drivers/ptp/Makefile      |   1 +
 drivers/ptp/ptp_dfl_tod.c | 333 ++++++++++++++++++++++++++++++++++++++
 4 files changed, 354 insertions(+)
 create mode 100644 drivers/ptp/ptp_dfl_tod.c

diff --git a/MAINTAINERS b/MAINTAINERS
index d8ebab595b2a..3fd603369464 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS

@@ -15623,6 +15623,13 @@ L:	netdev@vger.kernel.org
 S:	Maintained
 F:	drivers/ptp/ptp_ocp.c
 
+INTEL PTP DFL ToD DRIVER
+M:	Tianfei Zhang <tianfei.zhang@intel.com>
+L:	linux-fpga@vger.kernel.org
+L:	netdev@vger.kernel.org
+S:	Maintained
+F:	drivers/ptp/ptp_dfl_tod.c
+
 OPENCORES I2C BUS DRIVER
 M:	Peter Korsgaard <peter@korsgaard.com>
 M:	Andrew Lunn <andrew@lunn.ch>

diff --git a/drivers/ptp/Kconfig b/drivers/ptp/Kconfig
index fe4971b65c64..e0d6f136ee46 100644
--- a/drivers/ptp/Kconfig
+++ b/drivers/ptp/Kconfig

@@ -186,4 +186,17 @@ config PTP_1588_CLOCK_OCP
 
 	  More information is available at http://www.timingcard.com/
 
+config PTP_DFL_TOD
+	tristate "FPGA DFL ToD Driver"
+	depends on FPGA_DFL