[V10,0/7] Add driver support for Data Capture and Compare Engine(DCC) for SM8150,SC7280,SC7180,SDM845

DCC(Data Capture and Compare) is a DMA engine designed for debugging purposes.
In case of a system crash or manual software triggers by the user the DCC hardware
stores the value at the register addresses which can be used for debugging purposes.
The DCC driver provides the user with debugfs interface to configure the register
addresses. The options that the DCC hardware provides include reading from registers,
writing to registers, first reading and then writing to registers and looping
through the values of the same register.

In certain cases a register write needs to be executed for accessing the rest of the
registers, also the user might want to record the changing values of a register with
time for which he has the option to use the loop feature.

The options mentioned above are exposed to the user by debugfs files once the driver
is probed. The details and usage of this debugfs files are documented in
Documentation/ABI/testing/debugfs-driver-dcc.

As an example let us consider a couple of debug scenarios where DCC has been proved to be
effective for debugging purposes:-

i)TimeStamp Related Issue

On SC7180, there was a coresight timestamp issue where it would occasionally be all 0
instead of proper timestamp values.

Proper timestamp:
Idx:3373; ID:10; I_TIMESTAMP : Timestamp.; Updated val = 0x13004d8f5b7aa; CC=0x9e

Zero timestamp:
Idx:3387; ID:10; I_TIMESTAMP : Timestamp.; Updated val = 0x0; CC=0xa2

Now this is a non-fatal issue and doesn't need a system reset, but still needs
to be rootcaused and fixed for those who do care about coresight etm traces.
Since this is a timestamp issue, we would be looking for any timestamp related
clocks and such.

We get all the clk register details from IP documentation and configure it
via DCC config_read debugfs node. Before that we set the current linked list.

/* Program the linked list with the addresses */
echo R 0x10c004 > /sys/kernel/debug/dcc/../3/config
echo R 0x10c008 > /sys/kernel/debug/dcc/../3/config
echo R 0x10c00c > /sys/kernel/debug/dcc/../3/config
echo R 0x10c010 > /sys/kernel/debug/dcc/../3/config
..... and so on for other timestamp related clk registers

/* Other way of specifying is in "addr len" pair, in below case it
specifies to capture 4 words starting 0x10C004 */

echo R 0x10C004 4 > /sys/kernel/debug/dcc/../3/config_read

/* Enable DCC */
echo 1 > /sys/kernel/debug/dcc/../3/enable

/* Run the timestamp test for working case */

/* Send SW trigger */
echo 1 > /sys/kernel/debug/dcc/../trigger

/* Read SRAM */
cat /dev/dcc_sram > dcc_sram1.bin

/* Run the timestamp test for non-working case */

/* Send SW trigger */
echo 1 > /sys/kernel/debug/dcc/../trigger

/* Read SRAM */
cat /dev/dcc_sram > dcc_sram2.bin

Get the parser from [1] and checkout the latest branch.

/* Parse the SRAM bin */
python dcc_parser.py -s dcc_sram1.bin --v2 -o output/
python dcc_parser.py -s dcc_sram2.bin --v2 -o output/

Sample parsed output of dcc_sram1.bin:

<hwioDump version="1">
        <timestamp>03/14/21</timestamp>
            <generator>Linux DCC Parser</generator>
                <chip name="None" version="None">
                <register address="0x0010c004" value="0x80000000" />
                <register address="0x0010c008" value="0x00000008" />
                <register address="0x0010c00c" value="0x80004220" />
                <register address="0x0010c010" value="0x80000000" />
            </chip>
    <next_ll_offset>next_ll_offset : 0x1c </next_ll_offset>
</hwioDump>

ii)NOC register errors

A particular class of registers called NOC which are functional registers was reporting
errors while logging the values.To trace these errors the DCC has been used effectively.
The steps followed were similar to the ones mentioned above.
In addition to NOC registers a few other dependent registers were configured in DCC to
monitor it's values during a crash. A look at the dependent register values revealed that
the crash was happening due to a secured access to one of these dependent registers.
All these debugging activity and finding the root cause was achieved using DCC.

DCC parser is available at the following open source location

https://source.codeaurora.org/quic/la/platform/vendor/qcom-opensource/tools/tree/dcc_parser

Changes in V10

*The comments on version 9 are implemented.

Souradeep Chowdhury (7):
  dt-bindings: Added the yaml bindings for DCC
  soc: qcom: dcc:Add driver support for Data Capture and Compare
    unit(DCC)
  MAINTAINERS: Add the entry for DCC(Data Capture and Compare) driver
    support
  arm64: dts: qcom: sm8150: Add Data Capture and Compare(DCC) support
    node
  arm64: dts: qcom: sc7280: Add Data Capture and Compare(DCC) support
    node
  arm64: dts: qcom: sc7180: Add Data Capture and Compare(DCC) support
    node
  arm64: dts: qcom: sdm845: Add Data Capture and Compare(DCC) support
    node

 Documentation/ABI/testing/debugfs-driver-dcc       |   98 ++
 .../devicetree/bindings/arm/msm/qcom,dcc.yaml      |   44 +
 MAINTAINERS                                        |    8 +
 arch/arm64/boot/dts/qcom/sc7180.dtsi               |    6 +
 arch/arm64/boot/dts/qcom/sc7280.dtsi               |    6 +
 arch/arm64/boot/dts/qcom/sdm845.dtsi               |    6 +
 arch/arm64/boot/dts/qcom/sm8150.dtsi               |    6 +
 drivers/soc/qcom/Kconfig                           |    8 +
 drivers/soc/qcom/Makefile                          |    1 +
 drivers/soc/qcom/dcc.c                             | 1343 ++++++++++++++++++++
 10 files changed, 1526 insertions(+)
 create mode 100644 Documentation/ABI/testing/debugfs-driver-dcc
 create mode 100644 Documentation/devicetree/bindings/arm/msm/qcom,dcc.yaml
 create mode 100644 drivers/soc/qcom/dcc.c

On Thu, Sep 15, 2022 at 07:48:42PM +0530, Souradeep Chowdhury wrote:
> The DCC is a DMA Engine designed to capture and store data
> during system crash or software triggers. The DCC operates
> based on user inputs via the debugfs interface. The user gives
> addresses as inputs and these addresses are stored in the
> dcc sram. In case of a system crash or a manual software
> trigger by the user through the debugfs interface,
> the dcc captures and stores the values at these addresses.
> This patch contains the driver which has all the methods
> pertaining to the debugfs interface, auxiliary functions to
> support all the four fundamental operations of dcc namely
> read, write, read/modify/write and loop. The probe method
> here instantiates all the resources necessary for dcc to
> operate mainly the dedicated dcc sram where it stores the
> values. The DCC driver can be used for debugging purposes
> without going for a reboot since it can perform software
> triggers as well based on user inputs.
> 
> Also added the documentation for debugfs entries and explained
> the functionalities of each debugfs file that has been created
> for dcc.
> 
> The following is the justification of using debugfs interface
> over the other alternatives like sysfs/ioctls
> 
> i) As can be seen from the debugfs attribute descriptions,
> some of the debugfs attribute files here contains multiple
> arguments which needs to be accepted from the user. This goes
> against the design style of sysfs.
> 
> ii) The user input patterns have been made simple and convenient
> in this case with the use of debugfs interface as user doesn't
> need to shuffle between different files to execute one instruction
> as was the case on using other alternatives.
> 
> Signed-off-by: Souradeep Chowdhury <quic_schowdhu@quicinc.com>

Thanks for the respin Souradeep. checkpatch --strict still gives me 5
warnings and 49 checks, please fix 48 of those checks.


Please also add a space after "dcc:" in $subject.

Regards,
Bjorn