Re: [PATCH v5 2/2] Documentation: Add document for UltraSoc SMB drivers

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 16/04/2022 09:39, Qi Liu wrote:
> This patch bring in a documentation for UltraSoc SMB drivers.
> It simple descripts the device, sysfs interface and the
> firmware bindings.
> 
> Signed-off-by: Qi Liu <liuqi115@huawei.com>
> ---
>   .../trace/coresight/ultrasoc-smb.rst          | 79 +++++++++++++++++++
>   1 file changed, 79 insertions(+)
>   create mode 100644 Documentation/trace/coresight/ultrasoc-smb.rst
> 
> diff --git a/Documentation/trace/coresight/ultrasoc-smb.rst b/Documentation/trace/coresight/ultrasoc-smb.rst
> new file mode 100644
> index 000000000000..024fa4492f42
> --- /dev/null
> +++ b/Documentation/trace/coresight/ultrasoc-smb.rst
> @@ -0,0 +1,79 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +======================================
> +UltraSoc - HW Assisted Tracing on SoC
> +======================================
> +   :Author:   Qi Liu <liuqi115@huawei.com>
> +   :Date:     March 2022
> +
> +Introduction
> +------------
> +
> +UltraSoc SMB is a per SCCL hardware, and it provides a way to buffer and store

nit: what is SCCL ?

> +CPU trace messages in a region of shared system memory. SMB is plugged as
> +a coresight sink device and the corresponding trace generators (ETM) are
> +plugged in as source devices.
> +
> +Sysfs files and directories
> +---------------------------
> +
> +The SMB devices appear on the existing coresight bus alongside the other
> +coresight devices::
> +
> +	$# ls /sys/bus/coresight/devices/
> +	ultra_smb0   ultra_smb1   ultra_smb2   ultra_smb3
> +
> +The ``ultra_smb<N>`` named SMB associated with SCCL.::
> +
> +	$# ls /sys/bus/coresight/devices/ultra_smb0
> +	enable_sink   mgmt
> +	$# ls /sys/bus/coresight/devices/ultra_smb0/mgmt
> +	buf_size  buf_status  read_pos  write_pos
> +
> +*Key file items are:-*
> +   * ``read_pos``: Shows the value held by UltraSoc SMB Read Pointer register.
> +   * ``write_pos``: Shows the value held by UltraSoc SMB Write Pointer register.
> +   * ``buf_status``: Shows the value held by UltraSoc SMB status register.
> +		     BIT(0) is zero means buffer is empty.
> +   * ``buf_size``: Shows the buffer size of each UltraSoc SMB device.
> +
> +Firmware Bindings
> +---------------------------
> +
> +Firmware binding of SMB device describes SMB device indentifier, resource
> +information and graph structure.
> +
> +SMB is platform device and device id is "HISI03A1", resource of device is
> +declared using the _CRS method. Each SMB must present two base address,
> +the first one is the configuration base address of SMB device, the second
> +one is the base address of shared system memory.
> +
> +examples::
> +
> +    Device(USMB) {                                               \
> +      Name(_HID, "HISI03A1")                                     \
> +      Name(_CRS, ResourceTemplate() {                            \
> +          MEM_RESRC(0x95100000, 0x951FFFFF, 0x100000)            \
> +          MEM_RESRC(0x50000000, 0x53FFFFFF, 0x4000000)           \
> +      })                                                         \


> +      Name(_DSD, Package() {                                     \
> +        ToUUID("ab02a46b-74c7-45a2-bd68-f7d344ef2153"),          \

nit: May be add a comment here to explain, use Arm CoreSight Graph
ACPI bindings to describe the connections.

> +        Package() {                                              \
> +          0,                                                     \
> +          1,                                                     \
> +          Package() {                                            \
> +            1,                                                   \
> +            ToUUID("3ecbc8b6-1d0e-4fb3-8107-e627f805c6cd"),      \
> +            8,                                                   \
> +            Package() {0x8, 0, \_SB.S00.SL11.CL28.F008, 0},       \
> +            Package() {0x9, 0, \_SB.S00.SL11.CL29.F009, 0},       \
> +            Package() {0xa, 0, \_SB.S00.SL11.CL2A.F010, 0},       \
> +            Package() {0xb, 0, \_SB.S00.SL11.CL2B.F011, 0},       \
> +            Package() {0xc, 0, \_SB.S00.SL11.CL2C.F012, 0},       \
> +            Package() {0xd, 0, \_SB.S00.SL11.CL2D.F013, 0},       \
> +            Package() {0xe, 0, \_SB.S00.SL11.CL2E.F014, 0},       \
> +            Package() {0xf, 0, \_SB.S00.SL11.CL2F.F015, 0},       \
> +          }                                                      \

Interesting, are there multiple input ports for the SMB ? We haven't
seen an instance of a "sink" that supports this. So, would be
interesting to see how the driver copes with that scenario.

Suzuki



> +        }                                                        \
> +      })                                                         \
> +    }