summaryrefslogtreecommitdiffstats
path: root/Documentation/PCI/endpoint
diff options
context:
space:
mode:
authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-06 01:02:30 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-05-06 01:02:30 +0000
commit76cb841cb886eef6b3bee341a2266c76578724ad (patch)
treef5892e5ba6cc11949952a6ce4ecbe6d516d6ce58 /Documentation/PCI/endpoint
parentInitial commit. (diff)
downloadlinux-upstream/4.19.249.tar.xz
linux-upstream/4.19.249.zip
Adding upstream version 4.19.249.upstream/4.19.249upstream
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'Documentation/PCI/endpoint')
-rw-r--r--Documentation/PCI/endpoint/function/binding/pci-test.txt19
-rw-r--r--Documentation/PCI/endpoint/pci-endpoint-cfs.txt105
-rw-r--r--Documentation/PCI/endpoint/pci-endpoint.txt215
-rw-r--r--Documentation/PCI/endpoint/pci-test-function.txt87
-rw-r--r--Documentation/PCI/endpoint/pci-test-howto.txt203
5 files changed, 629 insertions, 0 deletions
diff --git a/Documentation/PCI/endpoint/function/binding/pci-test.txt b/Documentation/PCI/endpoint/function/binding/pci-test.txt
new file mode 100644
index 000000000..cd76ba473
--- /dev/null
+++ b/Documentation/PCI/endpoint/function/binding/pci-test.txt
@@ -0,0 +1,19 @@
+PCI TEST ENDPOINT FUNCTION
+
+name: Should be "pci_epf_test" to bind to the pci_epf_test driver.
+
+Configurable Fields:
+vendorid : should be 0x104c
+deviceid : should be 0xb500 for DRA74x and 0xb501 for DRA72x
+revid : don't care
+progif_code : don't care
+subclass_code : don't care
+baseclass_code : should be 0xff
+cache_line_size : don't care
+subsys_vendor_id : don't care
+subsys_id : don't care
+interrupt_pin : Should be 1 - INTA, 2 - INTB, 3 - INTC, 4 -INTD
+msi_interrupts : Should be 1 to 32 depending on the number of MSI interrupts
+ to test
+msix_interrupts : Should be 1 to 2048 depending on the number of MSI-X
+ interrupts to test
diff --git a/Documentation/PCI/endpoint/pci-endpoint-cfs.txt b/Documentation/PCI/endpoint/pci-endpoint-cfs.txt
new file mode 100644
index 000000000..d740f2996
--- /dev/null
+++ b/Documentation/PCI/endpoint/pci-endpoint-cfs.txt
@@ -0,0 +1,105 @@
+ CONFIGURING PCI ENDPOINT USING CONFIGFS
+ Kishon Vijay Abraham I <kishon@ti.com>
+
+The PCI Endpoint Core exposes configfs entry (pci_ep) to configure the
+PCI endpoint function and to bind the endpoint function
+with the endpoint controller. (For introducing other mechanisms to
+configure the PCI Endpoint Function refer to [1]).
+
+*) Mounting configfs
+
+The PCI Endpoint Core layer creates pci_ep directory in the mounted configfs
+directory. configfs can be mounted using the following command.
+
+ mount -t configfs none /sys/kernel/config
+
+*) Directory Structure
+
+The pci_ep configfs has two directories at its root: controllers and
+functions. Every EPC device present in the system will have an entry in
+the *controllers* directory and and every EPF driver present in the system
+will have an entry in the *functions* directory.
+
+/sys/kernel/config/pci_ep/
+ .. controllers/
+ .. functions/
+
+*) Creating EPF Device
+
+Every registered EPF driver will be listed in controllers directory. The
+entries corresponding to EPF driver will be created by the EPF core.
+
+/sys/kernel/config/pci_ep/functions/
+ .. <EPF Driver1>/
+ ... <EPF Device 11>/
+ ... <EPF Device 21>/
+ .. <EPF Driver2>/
+ ... <EPF Device 12>/
+ ... <EPF Device 22>/
+
+In order to create a <EPF device> of the type probed by <EPF Driver>, the
+user has to create a directory inside <EPF DriverN>.
+
+Every <EPF device> directory consists of the following entries that can be
+used to configure the standard configuration header of the endpoint function.
+(These entries are created by the framework when any new <EPF Device> is
+created)
+
+ .. <EPF Driver1>/
+ ... <EPF Device 11>/
+ ... vendorid
+ ... deviceid
+ ... revid
+ ... progif_code
+ ... subclass_code
+ ... baseclass_code
+ ... cache_line_size
+ ... subsys_vendor_id
+ ... subsys_id
+ ... interrupt_pin
+
+*) EPC Device
+
+Every registered EPC device will be listed in controllers directory. The
+entries corresponding to EPC device will be created by the EPC core.
+
+/sys/kernel/config/pci_ep/controllers/
+ .. <EPC Device1>/
+ ... <Symlink EPF Device11>/
+ ... <Symlink EPF Device12>/
+ ... start
+ .. <EPC Device2>/
+ ... <Symlink EPF Device21>/
+ ... <Symlink EPF Device22>/
+ ... start
+
+The <EPC Device> directory will have a list of symbolic links to
+<EPF Device>. These symbolic links should be created by the user to
+represent the functions present in the endpoint device.
+
+The <EPC Device> directory will also have a *start* field. Once
+"1" is written to this field, the endpoint device will be ready to
+establish the link with the host. This is usually done after
+all the EPF devices are created and linked with the EPC device.
+
+
+ | controllers/
+ | <Directory: EPC name>/
+ | <Symbolic Link: Function>
+ | start
+ | functions/
+ | <Directory: EPF driver>/
+ | <Directory: EPF device>/
+ | vendorid
+ | deviceid
+ | revid
+ | progif_code
+ | subclass_code
+ | baseclass_code
+ | cache_line_size
+ | subsys_vendor_id
+ | subsys_id
+ | interrupt_pin
+ | function
+
+[1] -> Documentation/PCI/endpoint/pci-endpoint.txt
diff --git a/Documentation/PCI/endpoint/pci-endpoint.txt b/Documentation/PCI/endpoint/pci-endpoint.txt
new file mode 100644
index 000000000..e86a96b66
--- /dev/null
+++ b/Documentation/PCI/endpoint/pci-endpoint.txt
@@ -0,0 +1,215 @@
+ PCI ENDPOINT FRAMEWORK
+ Kishon Vijay Abraham I <kishon@ti.com>
+
+This document is a guide to use the PCI Endpoint Framework in order to create
+endpoint controller driver, endpoint function driver, and using configfs
+interface to bind the function driver to the controller driver.
+
+1. Introduction
+
+Linux has a comprehensive PCI subsystem to support PCI controllers that
+operates in Root Complex mode. The subsystem has capability to scan PCI bus,
+assign memory resources and IRQ resources, load PCI driver (based on
+vendor ID, device ID), support other services like hot-plug, power management,
+advanced error reporting and virtual channels.
+
+However the PCI controller IP integrated in some SoCs is capable of operating
+either in Root Complex mode or Endpoint mode. PCI Endpoint Framework will
+add endpoint mode support in Linux. This will help to run Linux in an
+EP system which can have a wide variety of use cases from testing or
+validation, co-processor accelerator, etc.
+
+2. PCI Endpoint Core
+
+The PCI Endpoint Core layer comprises 3 components: the Endpoint Controller
+library, the Endpoint Function library, and the configfs layer to bind the
+endpoint function with the endpoint controller.
+
+2.1 PCI Endpoint Controller(EPC) Library
+
+The EPC library provides APIs to be used by the controller that can operate
+in endpoint mode. It also provides APIs to be used by function driver/library
+in order to implement a particular endpoint function.
+
+2.1.1 APIs for the PCI controller Driver
+
+This section lists the APIs that the PCI Endpoint core provides to be used
+by the PCI controller driver.
+
+*) devm_pci_epc_create()/pci_epc_create()
+
+ The PCI controller driver should implement the following ops:
+ * write_header: ops to populate configuration space header
+ * set_bar: ops to configure the BAR
+ * clear_bar: ops to reset the BAR
+ * alloc_addr_space: ops to allocate in PCI controller address space
+ * free_addr_space: ops to free the allocated address space
+ * raise_irq: ops to raise a legacy, MSI or MSI-X interrupt
+ * start: ops to start the PCI link
+ * stop: ops to stop the PCI link
+
+ The PCI controller driver can then create a new EPC device by invoking
+ devm_pci_epc_create()/pci_epc_create().
+
+*) devm_pci_epc_destroy()/pci_epc_destroy()
+
+ The PCI controller driver can destroy the EPC device created by either
+ devm_pci_epc_create() or pci_epc_create() using devm_pci_epc_destroy() or
+ pci_epc_destroy().
+
+*) pci_epc_linkup()
+
+ In order to notify all the function devices that the EPC device to which
+ they are linked has established a link with the host, the PCI controller
+ driver should invoke pci_epc_linkup().
+
+*) pci_epc_mem_init()
+
+ Initialize the pci_epc_mem structure used for allocating EPC addr space.
+
+*) pci_epc_mem_exit()
+
+ Cleanup the pci_epc_mem structure allocated during pci_epc_mem_init().
+
+2.1.2 APIs for the PCI Endpoint Function Driver
+
+This section lists the APIs that the PCI Endpoint core provides to be used
+by the PCI endpoint function driver.
+
+*) pci_epc_write_header()
+
+ The PCI endpoint function driver should use pci_epc_write_header() to
+ write the standard configuration header to the endpoint controller.
+
+*) pci_epc_set_bar()
+
+ The PCI endpoint function driver should use pci_epc_set_bar() to configure
+ the Base Address Register in order for the host to assign PCI addr space.
+ Register space of the function driver is usually configured
+ using this API.
+
+*) pci_epc_clear_bar()
+
+ The PCI endpoint function driver should use pci_epc_clear_bar() to reset
+ the BAR.
+
+*) pci_epc_raise_irq()
+
+ The PCI endpoint function driver should use pci_epc_raise_irq() to raise
+ Legacy Interrupt, MSI or MSI-X Interrupt.
+
+*) pci_epc_mem_alloc_addr()
+
+ The PCI endpoint function driver should use pci_epc_mem_alloc_addr(), to
+ allocate memory address from EPC addr space which is required to access
+ RC's buffer
+
+*) pci_epc_mem_free_addr()
+
+ The PCI endpoint function driver should use pci_epc_mem_free_addr() to
+ free the memory space allocated using pci_epc_mem_alloc_addr().
+
+2.1.3 Other APIs
+
+There are other APIs provided by the EPC library. These are used for binding
+the EPF device with EPC device. pci-ep-cfs.c can be used as reference for
+using these APIs.
+
+*) pci_epc_get()
+
+ Get a reference to the PCI endpoint controller based on the device name of
+ the controller.
+
+*) pci_epc_put()
+
+ Release the reference to the PCI endpoint controller obtained using
+ pci_epc_get()
+
+*) pci_epc_add_epf()
+
+ Add a PCI endpoint function to a PCI endpoint controller. A PCIe device
+ can have up to 8 functions according to the specification.
+
+*) pci_epc_remove_epf()
+
+ Remove the PCI endpoint function from PCI endpoint controller.
+
+*) pci_epc_start()
+
+ The PCI endpoint function driver should invoke pci_epc_start() once it
+ has configured the endpoint function and wants to start the PCI link.
+
+*) pci_epc_stop()
+
+ The PCI endpoint function driver should invoke pci_epc_stop() to stop
+ the PCI LINK.
+
+2.2 PCI Endpoint Function(EPF) Library
+
+The EPF library provides APIs to be used by the function driver and the EPC
+library to provide endpoint mode functionality.
+
+2.2.1 APIs for the PCI Endpoint Function Driver
+
+This section lists the APIs that the PCI Endpoint core provides to be used
+by the PCI endpoint function driver.
+
+*) pci_epf_register_driver()
+
+ The PCI Endpoint Function driver should implement the following ops:
+ * bind: ops to perform when a EPC device has been bound to EPF device
+ * unbind: ops to perform when a binding has been lost between a EPC
+ device and EPF device
+ * linkup: ops to perform when the EPC device has established a
+ connection with a host system
+
+ The PCI Function driver can then register the PCI EPF driver by using
+ pci_epf_register_driver().
+
+*) pci_epf_unregister_driver()
+
+ The PCI Function driver can unregister the PCI EPF driver by using
+ pci_epf_unregister_driver().
+
+*) pci_epf_alloc_space()
+
+ The PCI Function driver can allocate space for a particular BAR using
+ pci_epf_alloc_space().
+
+*) pci_epf_free_space()
+
+ The PCI Function driver can free the allocated space
+ (using pci_epf_alloc_space) by invoking pci_epf_free_space().
+
+2.2.2 APIs for the PCI Endpoint Controller Library
+This section lists the APIs that the PCI Endpoint core provides to be used
+by the PCI endpoint controller library.
+
+*) pci_epf_linkup()
+
+ The PCI endpoint controller library invokes pci_epf_linkup() when the
+ EPC device has established the connection to the host.
+
+2.2.2 Other APIs
+There are other APIs provided by the EPF library. These are used to notify
+the function driver when the EPF device is bound to the EPC device.
+pci-ep-cfs.c can be used as reference for using these APIs.
+
+*) pci_epf_create()
+
+ Create a new PCI EPF device by passing the name of the PCI EPF device.
+ This name will be used to bind the the EPF device to a EPF driver.
+
+*) pci_epf_destroy()
+
+ Destroy the created PCI EPF device.
+
+*) pci_epf_bind()
+
+ pci_epf_bind() should be invoked when the EPF device has been bound to
+ a EPC device.
+
+*) pci_epf_unbind()
+
+ pci_epf_unbind() should be invoked when the binding between EPC device
+ and EPF device is lost.
diff --git a/Documentation/PCI/endpoint/pci-test-function.txt b/Documentation/PCI/endpoint/pci-test-function.txt
new file mode 100644
index 000000000..5916f1f59
--- /dev/null
+++ b/Documentation/PCI/endpoint/pci-test-function.txt
@@ -0,0 +1,87 @@
+ PCI TEST
+ Kishon Vijay Abraham I <kishon@ti.com>
+
+Traditionally PCI RC has always been validated by using standard
+PCI cards like ethernet PCI cards or USB PCI cards or SATA PCI cards.
+However with the addition of EP-core in linux kernel, it is possible
+to configure a PCI controller that can operate in EP mode to work as
+a test device.
+
+The PCI endpoint test device is a virtual device (defined in software)
+used to test the endpoint functionality and serve as a sample driver
+for other PCI endpoint devices (to use the EP framework).
+
+The PCI endpoint test device has the following registers:
+
+ 1) PCI_ENDPOINT_TEST_MAGIC
+ 2) PCI_ENDPOINT_TEST_COMMAND
+ 3) PCI_ENDPOINT_TEST_STATUS
+ 4) PCI_ENDPOINT_TEST_SRC_ADDR
+ 5) PCI_ENDPOINT_TEST_DST_ADDR
+ 6) PCI_ENDPOINT_TEST_SIZE
+ 7) PCI_ENDPOINT_TEST_CHECKSUM
+ 8) PCI_ENDPOINT_TEST_IRQ_TYPE
+ 9) PCI_ENDPOINT_TEST_IRQ_NUMBER
+
+*) PCI_ENDPOINT_TEST_MAGIC
+
+This register will be used to test BAR0. A known pattern will be written
+and read back from MAGIC register to verify BAR0.
+
+*) PCI_ENDPOINT_TEST_COMMAND:
+
+This register will be used by the host driver to indicate the function
+that the endpoint device must perform.
+
+Bitfield Description:
+ Bit 0 : raise legacy IRQ
+ Bit 1 : raise MSI IRQ
+ Bit 2 : raise MSI-X IRQ
+ Bit 3 : read command (read data from RC buffer)
+ Bit 4 : write command (write data to RC buffer)
+ Bit 5 : copy command (copy data from one RC buffer to another
+ RC buffer)
+
+*) PCI_ENDPOINT_TEST_STATUS
+
+This register reflects the status of the PCI endpoint device.
+
+Bitfield Description:
+ Bit 0 : read success
+ Bit 1 : read fail
+ Bit 2 : write success
+ Bit 3 : write fail
+ Bit 4 : copy success
+ Bit 5 : copy fail
+ Bit 6 : IRQ raised
+ Bit 7 : source address is invalid
+ Bit 8 : destination address is invalid
+
+*) PCI_ENDPOINT_TEST_SRC_ADDR
+
+This register contains the source address (RC buffer address) for the
+COPY/READ command.
+
+*) PCI_ENDPOINT_TEST_DST_ADDR
+
+This register contains the destination address (RC buffer address) for
+the COPY/WRITE command.
+
+*) PCI_ENDPOINT_TEST_IRQ_TYPE
+
+This register contains the interrupt type (Legacy/MSI) triggered
+for the READ/WRITE/COPY and raise IRQ (Legacy/MSI) commands.
+
+Possible types:
+ - Legacy : 0
+ - MSI : 1
+ - MSI-X : 2
+
+*) PCI_ENDPOINT_TEST_IRQ_NUMBER
+
+This register contains the triggered ID interrupt.
+
+Admissible values:
+ - Legacy : 0
+ - MSI : [1 .. 32]
+ - MSI-X : [1 .. 2048]
diff --git a/Documentation/PCI/endpoint/pci-test-howto.txt b/Documentation/PCI/endpoint/pci-test-howto.txt
new file mode 100644
index 000000000..e40cf0fb5
--- /dev/null
+++ b/Documentation/PCI/endpoint/pci-test-howto.txt
@@ -0,0 +1,203 @@
+ PCI TEST USERGUIDE
+ Kishon Vijay Abraham I <kishon@ti.com>
+
+This document is a guide to help users use pci-epf-test function driver
+and pci_endpoint_test host driver for testing PCI. The list of steps to
+be followed in the host side and EP side is given below.
+
+1. Endpoint Device
+
+1.1 Endpoint Controller Devices
+
+To find the list of endpoint controller devices in the system:
+
+ # ls /sys/class/pci_epc/
+ 51000000.pcie_ep
+
+If PCI_ENDPOINT_CONFIGFS is enabled
+ # ls /sys/kernel/config/pci_ep/controllers
+ 51000000.pcie_ep
+
+1.2 Endpoint Function Drivers
+
+To find the list of endpoint function drivers in the system:
+
+ # ls /sys/bus/pci-epf/drivers
+ pci_epf_test
+
+If PCI_ENDPOINT_CONFIGFS is enabled
+ # ls /sys/kernel/config/pci_ep/functions
+ pci_epf_test
+
+1.3 Creating pci-epf-test Device
+
+PCI endpoint function device can be created using the configfs. To create
+pci-epf-test device, the following commands can be used
+
+ # mount -t configfs none /sys/kernel/config
+ # cd /sys/kernel/config/pci_ep/
+ # mkdir functions/pci_epf_test/func1
+
+The "mkdir func1" above creates the pci-epf-test function device that will
+be probed by pci_epf_test driver.
+
+The PCI endpoint framework populates the directory with the following
+configurable fields.
+
+ # ls functions/pci_epf_test/func1
+ baseclass_code interrupt_pin progif_code subsys_id
+ cache_line_size msi_interrupts revid subsys_vendorid
+ deviceid msix_interrupts subclass_code vendorid
+
+The PCI endpoint function driver populates these entries with default values
+when the device is bound to the driver. The pci-epf-test driver populates
+vendorid with 0xffff and interrupt_pin with 0x0001
+
+ # cat functions/pci_epf_test/func1/vendorid
+ 0xffff
+ # cat functions/pci_epf_test/func1/interrupt_pin
+ 0x0001
+
+1.4 Configuring pci-epf-test Device
+
+The user can configure the pci-epf-test device using configfs entry. In order
+to change the vendorid and the number of MSI interrupts used by the function
+device, the following commands can be used.
+
+ # echo 0x104c > functions/pci_epf_test/func1/vendorid
+ # echo 0xb500 > functions/pci_epf_test/func1/deviceid
+ # echo 16 > functions/pci_epf_test/func1/msi_interrupts
+ # echo 8 > functions/pci_epf_test/func1/msix_interrupts
+
+1.5 Binding pci-epf-test Device to EP Controller
+
+In order for the endpoint function device to be useful, it has to be bound to
+a PCI endpoint controller driver. Use the configfs to bind the function
+device to one of the controller driver present in the system.
+
+ # ln -s functions/pci_epf_test/func1 controllers/51000000.pcie_ep/
+
+Once the above step is completed, the PCI endpoint is ready to establish a link
+with the host.
+
+1.6 Start the Link
+
+In order for the endpoint device to establish a link with the host, the _start_
+field should be populated with '1'.
+
+ # echo 1 > controllers/51000000.pcie_ep/start
+
+2. RootComplex Device
+
+2.1 lspci Output
+
+Note that the devices listed here correspond to the value populated in 1.4 above
+
+ 00:00.0 PCI bridge: Texas Instruments Device 8888 (rev 01)
+ 01:00.0 Unassigned class [ff00]: Texas Instruments Device b500
+
+2.2 Using Endpoint Test function Device
+
+pcitest.sh added in tools/pci/ can be used to run all the default PCI endpoint
+tests. Before pcitest.sh can be used pcitest.c should be compiled using the
+following commands.
+
+ cd <kernel-dir>
+ make headers_install ARCH=arm
+ arm-linux-gnueabihf-gcc -Iusr/include tools/pci/pcitest.c -o pcitest
+ cp pcitest <rootfs>/usr/sbin/
+ cp tools/pci/pcitest.sh <rootfs>
+
+2.2.1 pcitest.sh Output
+ # ./pcitest.sh
+ BAR tests
+
+ BAR0: OKAY
+ BAR1: OKAY
+ BAR2: OKAY
+ BAR3: OKAY
+ BAR4: NOT OKAY
+ BAR5: NOT OKAY
+
+ Interrupt tests
+
+ SET IRQ TYPE TO LEGACY: OKAY
+ LEGACY IRQ: NOT OKAY
+ SET IRQ TYPE TO MSI: OKAY
+ MSI1: OKAY
+ MSI2: OKAY
+ MSI3: OKAY
+ MSI4: OKAY
+ MSI5: OKAY
+ MSI6: OKAY
+ MSI7: OKAY
+ MSI8: OKAY
+ MSI9: OKAY
+ MSI10: OKAY
+ MSI11: OKAY
+ MSI12: OKAY
+ MSI13: OKAY
+ MSI14: OKAY
+ MSI15: OKAY
+ MSI16: OKAY
+ MSI17: NOT OKAY
+ MSI18: NOT OKAY
+ MSI19: NOT OKAY
+ MSI20: NOT OKAY
+ MSI21: NOT OKAY
+ MSI22: NOT OKAY
+ MSI23: NOT OKAY
+ MSI24: NOT OKAY
+ MSI25: NOT OKAY
+ MSI26: NOT OKAY
+ MSI27: NOT OKAY
+ MSI28: NOT OKAY
+ MSI29: NOT OKAY
+ MSI30: NOT OKAY
+ MSI31: NOT OKAY
+ MSI32: NOT OKAY
+ SET IRQ TYPE TO MSI-X: OKAY
+ MSI-X1: OKAY
+ MSI-X2: OKAY
+ MSI-X3: OKAY
+ MSI-X4: OKAY
+ MSI-X5: OKAY
+ MSI-X6: OKAY
+ MSI-X7: OKAY
+ MSI-X8: OKAY
+ MSI-X9: NOT OKAY
+ MSI-X10: NOT OKAY
+ MSI-X11: NOT OKAY
+ MSI-X12: NOT OKAY
+ MSI-X13: NOT OKAY
+ MSI-X14: NOT OKAY
+ MSI-X15: NOT OKAY
+ MSI-X16: NOT OKAY
+ [...]
+ MSI-X2047: NOT OKAY
+ MSI-X2048: NOT OKAY
+
+ Read Tests
+
+ SET IRQ TYPE TO MSI: OKAY
+ READ ( 1 bytes): OKAY
+ READ ( 1024 bytes): OKAY
+ READ ( 1025 bytes): OKAY
+ READ (1024000 bytes): OKAY
+ READ (1024001 bytes): OKAY
+
+ Write Tests
+
+ WRITE ( 1 bytes): OKAY
+ WRITE ( 1024 bytes): OKAY
+ WRITE ( 1025 bytes): OKAY
+ WRITE (1024000 bytes): OKAY
+ WRITE (1024001 bytes): OKAY
+
+ Copy Tests
+
+ COPY ( 1 bytes): OKAY
+ COPY ( 1024 bytes): OKAY
+ COPY ( 1025 bytes): OKAY
+ COPY (1024000 bytes): OKAY
+ COPY (1024001 bytes): OKAY