media: Documentation: add documentation of Intel IPU6 driver and hardware overview

Add a documentation for an overview of IPU6 hardware and describe the main
the components of IPU6 driver.
Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

Documentation/driver-api/media/drivers/index.rst

@@ -26,6 +26,7 @@ Video4Linux (V4L) drivers
 	vimc-devel
 	zoran
 	ccs/ccs
+	ipu6
 
 
 Digital TV drivers

Documentation/driver-api/media/drivers/ipu6.rst

+.. SPDX-License-Identifier: GPL-2.0
+
+==================
+Intel IPU6 Driver
+==================
+
+Author: Bingbu Cao <bingbu.cao@intel.com>
+
+Overview
+=========
+
+Intel IPU6 is the sixth generation of Intel Image Processing Unit used in some
+Intel Chipsets such as Tiger Lake, Jasper Lake, Alder Lake, Raptor Lake and
+Meteor Lake. IPU6 consists of two major systems: Input System (ISYS) and
+Processing System (PSYS). IPU6 are visible on the PCI bus as a single device, it
+can be found by ``lspci``:
+
+``0000:00:05.0 Multimedia controller: Intel Corporation Device xxxx (rev xx)``
+
+IPU6 has a 16 MB BAR in PCI configuration Space for MMIO registers which is
+visible for driver.
+
+Buttress
+=========
+
+The IPU6 is connecting to the system fabric with Buttress which is enabling host
+driver to control the IPU6, it also allows IPU6 access the system memory to
+store and load frame pixel streams and any other metadata.
+
+Buttress mainly manages several system functionalities: power management,
+interrupt handling, firmware authentication and global timer sync.
+
+ISYS and PSYS Power flow
+------------------------
+
+IPU6 driver initialize the ISYS and PSYS power up or down request by setting the
+Buttress frequency control register for ISYS and PSYS
+(``IPU6_BUTTRESS_REG_IS_FREQ_CTL`` and ``IPU6_BUTTRESS_REG_PS_FREQ_CTL``) in
+function:
+
+.. c:function:: int ipu6_buttress_power(...)
+
+Buttress forwards the request to Punit, after Punit execute the power up flow,
+Buttress indicates driver that ISYS or PSYS is powered up by updating the power
+status registers.
+
+.. Note:: ISYS power up needs take place prior to PSYS power up, ISYS power down
+	  needs take place after PSYS power down due to hardware limitation.
+
+Interrupt
+---------
+
+IPU6 interrupt can be generated as MSI or INTA, interrupt will be triggered when
+ISYS, PSYS, Buttress event or error happen, driver can get the interrupt cause
+by reading the interrupt status register ``BUTTRESS_REG_ISR_STATUS``, driver
+clears the irq status and then calls specific ISYS or PSYS irq handler.
+
+.. c:function:: irqreturn_t ipu6_buttress_isr(int irq, ...)
+
+Security and firmware authentication
+-------------------------------------
+
+To address the IPU6 firmware security concerns, the IPU6 firmware needs to
+undergo an authentication process before it is allowed to executed on the IPU6
+internal processors. The IPU6 driver will work with Converged Security Engine
+(CSE) to complete authentication process. The CSE is responsible of
+authenticating the IPU6 firmware. The authenticated firmware binary is copied
+into an isolated memory region. Firmware authentication process is implemented
+by CSE following an IPC handshake with the IPU6 driver. There are some Buttress
+registers used by the CSE and the IPU6 driver to communicate with each other via
+IPC.
+
+.. c:function:: int ipu6_buttress_authenticate(...)
+
+Global timer sync
+-----------------
+
+The IPU6 driver initiates a Hammock Harbor synchronization flow each time it
+starts camera operation. The IPU6 will synchronizes an internal counter in the
+Buttress with a copy of the SoC time, this counter maintains the up-to-date time
+until camera operation is stopped. The IPU6 driver can use this time counter to
+calibrate the timestamp based on the timestamp in response event from firmware.
+
+.. c:function:: int ipu6_buttress_start_tsc_sync(...)
+
+DMA and MMU
+============
+
+The IPU6 has its own scalar processor where the firmware run at and an internal
+32-bit virtual address space. The IPU6 has MMU address translation hardware to
+allow that scalar processors to access the internal memory and external system
+memory through IPU6 virtual address. The address translation is based on two
+levels of page lookup tables stored in system memory which are maintained by the
+IPU6 driver. The IPU6 driver sets the level-1 page table base address to MMU
+register and allows MMU to perform page table lookups.
+
+The IPU6 driver exports its own DMA operations. The IPU6 driver will update the
+page table entries for each DMA operation and invalidate the MMU TLB after each
+unmap and free.
+
+.. code-block:: none
+
+    const struct dma_map_ops ipu6_dma_ops = {
+	   .alloc = ipu6_dma_alloc,
+	   .free = ipu6_dma_free,
+	   .mmap = ipu6_dma_mmap,
+	   .map_sg = ipu6_dma_map_sg,
+	   .unmap_sg = ipu6_dma_unmap_sg,
+	   ...
+    };
+
+.. Note:: IPU6 MMU works behind IOMMU so for each IPU6 DMA ops, driver will call
+	  generic PCI DMA ops to ask IOMMU to do the additional mapping if VT-d
+	  enabled.
+
+Firmware file format
+====================
+
+The IPU6 firmware is in Code Partition Directory (CPD) file format. The CPD
+firmware contains a CPD header, several CPD entries and components. The CPD
+component includes 3 entries - manifest, metadata and module data. Manifest and
+metadata are defined by CSE and used by CSE for authentication. Module data is
+specific to IPU6 which holds the binary data of firmware called package
+directory. The IPU6 driver (``ipu6-cpd.c`` in particular) parses and validates
+the CPD firmware file and gets the package directory binary data of the IPU6
+firmware, copies it to specific DMA buffer and sets its base address to Buttress
+``FW_SOURCE_BASE`` register. Finally the CSE will do authentication for this
+firmware binary.
+
+
+Syscom interface
+================
+
+The IPU6 driver communicates with firmware via the Syscom ABI. Syscom is an
+inter-processor communication mechanism between the IPU scalar processors and
+the CPU. There are a number of resources shared between firmware and software.
+A system memory region where the message queues reside, firmware can access the
+memory region via the IPU MMU. The Syscom queues are FIFO fixed depth queues
+with a configurable number of tokens (messages). There are also common IPU6 MMIO
+registers where the queue read and write indices reside. Software and firmware
+function as producer and consumer of tokens in the queues and update the write
+and read indices separately when sending or receiving each message.
+
+The IPU6 driver must prepare and configure the number of input and output
+queues, configure the count of tokens per queue and the size of per token before
+initiating and starting the communication with firmware. Firmware and software
+must use same configurations. The IPU6 Buttress has a number of firmware boot
+parameter registers which can be used to store the address of configuration and
+initialise the Syscom state, then driver can request firmware to start and run via
+setting the scalar processor control status register.
+
+Input System
+============
+
+IPU6 input system consists of MIPI D-PHY and several CSI-2 receivers.  It can
+capture image pixel data from camera sensors or other MIPI CSI-2 output devices.
+
+D-PHYs and CSI-2 ports lane mapping
+-----------------------------------
+
+The IPU6 integrates different D-PHY IPs on different SoCs, on Tiger Lake and
+Alder Lake, IPU6 integrates MCD10 D-PHY, IPU6SE on Jasper Lake integrates JSL
+D-PHY and IPU6EP on Meteor Lake integrates a Synopsys DWC D-PHY. There is an
+adaptional layer between D-PHY and CSI-2 receiver controller which includes port
+configuration, PHY wrapper or private test interfaces for D-PHY. There are 3
+D-PHY drivers ``ipu6-isys-mcd-phy.c``, ``ipu6-isys-jsl-phy.c`` and
+``ipu6-isys-dwc-phy.c`` program the above 3 D-PHYs in IPU6.
+
+Different IPU6 versions have different D-PHY lanes mappings, On Tiger Lake,
+there are 12 data lanes and 8 clock lanes, IPU6 support maximum 8 CSI-2 ports,
+see the PPI mmapping in ``ipu6-isys-mcd-phy.c`` for more information. On Jasper
+Lake and Alder Lake, D-PHY has 8 data lanes and 4 clock lanes, the IPU6 supports
+maximum 4 CSI-2 ports. For Meteor Lake, D-PHY has 12 data lanes and 6 clock
+lanes so IPU6 support maximum 6 CSI-2 ports.
+
+.. Note:: Each pair of CSI-2 two ports is a single unit that can share the data
+	  lanes. For example, for CSI-2 port 0 and 1, CSI-2 port 0 support
+	  maximum 4 data lanes, CSI-2 port 1 support maximum 2 data lanes, CSI-2
+	  port 0 with 2 data lanes can work together with CSI-2 port 1 with 2
+	  data lanes. If trying to use CSI-2 port 0 with 4 lanes, CSI-2 port 1
+	  will not be available as the 4 data lanes are shared by CSI-2 port 0
+	  and 1. The same applies to CSI ports 2/3, 4/5 and 7/8.
+
+ISYS firmware ABIs
+------------------
+
+The IPU6 firmware implements a series of ABIs for software access. In general,
+software firstly prepares the stream configuration ``struct
+ipu6_fw_isys_stream_cfg_data_abi`` and sends the configuration to firmware via
+sending ``STREAM_OPEN`` command. Stream configuration includes input pins and
+output pins, input pin ``struct ipu6_fw_isys_input_pin_info_abi`` defines the
+resolution and data type of input source, output pin ``struct
+ipu6_fw_isys_output_pin_info_abi`` defines the output resolution, stride and
+frame format, etc.
+
+Once the driver gets the interrupt from firmware that indicates stream open
+successfully, the driver will send the ``STREAM_START`` and ``STREAM_CAPTURE``
+command to request firmware to start capturing image frames. ``STREAM_CAPTURE``
+command queues the buffers to firmware with ``struct
+ipu6_fw_isys_frame_buff_set``, software then waits for the interrupt and
+response from firmware, ``PIN_DATA_READY`` means a buffer is ready on a specific
+output pin and then software can return the buffer to user.
+
+.. Note:: See :ref:`Examples<ipu6_isys_capture_examples>` about how to do
+	  capture by IPU6 ISYS driver.