Re: [PATCH v2 15/15] Documentation: add documentation of Intel IPU6 driver and hardware overview

[Bingbu Cao <bingbu.cao@linux.intel.com>]

Sakari,

Thanks for the review.

On 10/25/23 8:09 PM, Sakari Ailus wrote:
> Hi Bingbu,
> 
> Thanks for the patch. It's a nice piece of documentation for the most
> complex CSI-2 receiver driver. :-)
> 
> On Tue, Oct 24, 2023 at 07:29:24PM +0800, bingbu.cao@intel.com wrote:
>> From: Bingbu Cao <bingbu.cao@intel.com>
>>
>> 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>
>> ---
>>  .../driver-api/media/drivers/index.rst        |   1 +
>>  .../driver-api/media/drivers/ipu6.rst         | 205 ++++++++++++++++++
>>  2 files changed, 206 insertions(+)
>>  create mode 100644 Documentation/driver-api/media/drivers/ipu6.rst
>>
>> diff --git a/Documentation/driver-api/media/drivers/index.rst b/Documentation/driver-api/media/drivers/index.rst
>> index c4123a16b5f9..7f6f3dcd5c90 100644
>> --- a/Documentation/driver-api/media/drivers/index.rst
>> +++ b/Documentation/driver-api/media/drivers/index.rst
>> @@ -26,6 +26,7 @@ Video4Linux (V4L) drivers
>>  	vimc-devel
>>  	zoran
>>  	ccs/ccs
>> +	ipu6
>>  
>>  
>>  Digital TV drivers
>> diff --git a/Documentation/driver-api/media/drivers/ipu6.rst b/Documentation/driver-api/media/drivers/ipu6.rst
>> new file mode 100644
>> index 000000000000..2685e4a0d7ba
>> --- /dev/null
>> +++ b/Documentation/driver-api/media/drivers/ipu6.rst
>> @@ -0,0 +1,205 @@
>> +.. 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 (IS) and
> 
> I'd use a semicolon:				  ^

semicolon or colon? :)

> 
>> +Processing System (PS). 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.
>> +
>> +IS and PS Power flow
>> +---------------------------
>> +
>> +IPU6 driver initialize the IS and PS power up or down request by setting the
>> +Buttress frequency control register for IS and PS -
>> +``IPU6_BUTTRESS_REG_IS_FREQ_CTL`` and ``IPU6_BUTTRESS_REG_PS_FREQ_CTL`` in
>> +function:
>> +
>> +.. c:function:: int ipu6_buttress_power(..., bool on)
>> +
>> +Buttress forwards the request to Punit, after Punit execute the power up flow,
>> +buttress indicates driver that IS or PS is powered up by updating the power
>> +status registers.
>> +
>> +.. Note:: IS power up needs take place prior to PS power up, IS power down needs
>> +	  take place after PS power down due to hardware limitation.
>> +
>> +
>> +Interrupt
>> +------------
>> +
>> +IPU6 interrupt can be generated as MSI or INTA, interrupt will be triggered
>> +when IS, PS, Buttress event or error happen, driver can get the interrupt
>> +cause by reading the interrupt status register ``BUTTRESS_REG_ISR_STATUS``,
>> +driver firstly clear the irq status and then call specific IS or PS 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. Driver will work with Converged Security Engine (CSE) to
>> +complete authentication process. 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 driver. There are some Buttress registers used by CSE and
>> +driver to communicate with each other as IPC messages.
>> +
>> +.. c:function:: int ipu6_buttress_authenticate(...)
>> +
>> +Global timer sync
>> +------------------
>> +IPU driver initiates a Hammock Harbor synchronization flow each time it starts
>> +camera operation. IPU will synchronizes an internal counter in the Buttress
>> +with a copy of SoC time, this counter keeps the updated time until camera
>> +operation is stopped. 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
>> +============
>> +
>> +IPU6 has its own scalar processor where the firmware run at, it has
>> +an internal 32-bits virtual address space. IPU6 has MMU address translation
>> +hardware to allow that scalar process 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 IPU6 driver. IPU6 driver sets the level-1 page table base address
>> +to MMU register and allow MMU to lookup the page table.
>> +
>> +IPU6 driver exports its own DMA operations. 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
>> +=====================
>> +
>> +IPU6 release the firmware in Code Partition Directory (CPD) file format. The
>> +CPD firmware contains a CPD header, several CPD entries and CPD components.
>> +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 defined by IPU6 which holds the binary data of firmware called package
>> +directory. IPU6 driver (``ipu6-cpd.c``) parses and validates the CPD firmware
>> +file and get the package directory binary data of IPU6 firmware, copy it to
>> +specific DMA buffer and sets its base address to Buttress ``FW_SOURCE_BASE``
>> +register, CSE will do authentication for this firmware binary.
>> +
>> +
>> +Syscom interface
>> +================
>> +
>> +IPU6 driver communicates with firmware via syscom ABI. Syscom is an
>> +inter-processor communication mechanism between IPU scalar processor and 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 IPU MMU. Syscom queues are FIFO fixed depth queues with
>> +configurable elements ``token`` (message). There is also a common IPU MMIO
>> +registers where the queue read and write indices reside. Software and firmware
>> +work as producer and consumer of tokens in queue, and update the write and read
>> +indices separately when sending or receiving each message.
>> +
>> +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
>> +initiate and start the communication with firmware, firmware and software must
>> +use same configurations. IPU6 Buttress has a number of firmware boot parameter
>> +registers which can be used to store the address of configuration and initiate
>> +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 receiver controllers,
>> +it can capture image pixel data from camera sensors or other MIPI CSI output
>> +devices.
>> +
>> +DPHYs and CSI2 ports lane mapping
> 
> "D-PHY" and "CSI-2"

Ack.

> 
>> +---------------------------------
>> +
>> +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 adaption
>> +layer between D-PHY and CSI 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 version has different DPHY lanes mappings, On Tiger Lake, there
>> +are 12 data lanes and 8 clock lanes, IPU6 support maximum 8 CSI2 ports, see
>> +the ppi mmapping in ``ipu6-isys-mcd-phy.c`` for more information. On Jasper Lake
>> +and Alder Lake, DPHY has 8 data lanes and 4 clock lanes, IPU6 support maximum 4
>> +CSI2 ports. For Meteor Lake, DPHY has 12 data lanes and 6 clock lanes, IPU6
>> +support maximum 6 CSI2 ports.
>> +
>> +.. Note:: Each adjacent CSI ports work as a pair and share the data lanes.
>> +	  For example, for CSI port 0 and 1, CSI port 0 support maximum 4
>> +	  data lanes, CSI port 1 support maximum 2 data lanes, CSI port 0
>> +	  with 2 data lanes can work together with CSI port 1 with 2 data lanes.
>> +	  If trying to use CSI port 0 with 4 lanes, CSI port 1 will not be
>> +	  available as the 4 data lanes are shared by CSI port 0 and 1. Same
>> +	  scenario is also applied for CSI port 2/3, 4/5 and 7/8.
>> +
>> +IS firmware ABIs
>> +----------------
>> +
>> +IPU6 firmware define a series of ABIs to software. In general, software firstly
>> +prepare the stream configuration ``struct ipu6_fw_isys_stream_cfg_data_abi``
>> +and send 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 driver get the
>> +interrupt from firmware that indicates stream open successfully, 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 wait the
>> +interrupt and response from firmware, ``PIN_DATA_READY`` means data ready
>> +on specific output pin and then software return the buffers to user.
>> +
>> +.. Note:: See Documentation/admin-guide/media/ipu6-isys.rst for how to do
> 
> Could you add a direct link instead? See e.g.
> Documentation/driver-api/media/camera-sensor.rst for an example.

Good idea, thanks.

> 
>> +	  capture by IPU6 IS driver.
>> +
>> +
> 

-- 
Best regards,
Bingbu Cao