[PATCH V7 2/7] soc: qcom: dcc:Add driver support for Data Capture and Compare unit(DCC)
Bjorn Andersson
bjorn.andersson at linaro.org
Tue May 3 11:03:09 PDT 2022
On Thu 03 Mar 00:27 CST 2022, 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 sysfs 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 at quicinc.com>
> ---
> Documentation/ABI/testing/debugfs-driver-dcc | 124 +++
> drivers/soc/qcom/Kconfig | 8 +
> drivers/soc/qcom/Makefile | 1 +
> drivers/soc/qcom/dcc.c | 1465 ++++++++++++++++++++++++++
> 4 files changed, 1598 insertions(+)
> create mode 100644 Documentation/ABI/testing/debugfs-driver-dcc
> create mode 100644 drivers/soc/qcom/dcc.c
>
> diff --git a/Documentation/ABI/testing/debugfs-driver-dcc b/Documentation/ABI/testing/debugfs-driver-dcc
> new file mode 100644
> index 0000000..70029ab
> --- /dev/null
> +++ b/Documentation/ABI/testing/debugfs-driver-dcc
> @@ -0,0 +1,124 @@
> +What: /sys/kernel/debug/dcc/.../trigger
> +Date: March 2022
> +Contact: Souradeep Chowdhury <quic_schowdhu at quicinc.com>
> +Description:
> + This is the debugfs interface for manual software
> + triggers. The user can simply enter a 1 against
> + the debugfs file and enable a manual trigger.
> + Example:
> + echo 1 > /sys/kernel/debug/dcc/.../trigger
> +
> +What: /sys/kernel/debug/dcc/.../enable
> +Date: March 2022
> +Contact: Souradeep Chowdhury <quic_schowdhu at quicinc.com>
> +Description:
> + This debugfs interface is used for enabling the
> + the dcc hardware. On enabling the dcc, all the
> + addresses entered by the user is written into
> + dcc sram which is read by the dcc hardware on
> + manual or crash induced triggers.
> + Example:
> + echo 0 > /sys/bus/platform/devices/.../enable
> + (disable dcc)
> + echo 1 > /sys/bus/platform/devices/.../enable
> + (enable dcc)
> +
> +What: /sys/kernel/debug/dcc/.../config_read
As mentioned last time, I don't like this interface of having 6 files
that the user can write to in order to append items in the currently
selected linked list.
Why can't this be a single "config" which takes a multiline string of
operations? (Bonus point for supporting appending to the list).
This would also serve as a natural place to dump the linked list back to
the user for inspection.
> +Date: March 2022
> +Contact: Souradeep Chowdhury <quic_schowdhu at quicinc.com>
> +Description:
> + This stores the addresses of the registers which
> + needs to be read in case of a hardware crash or
> + manual software triggers. The address entered here
> + are considered under read type instruction.
> + Example:
> + echo <1> <2> <3> >/sys/kernel/debug/dcc/../config_read
> + 1->Address to be considered for reading the value.
> + 2->The word count of the addresses, read n words
> + starting from address <1>.
> + 3->Can be a 1 or 0 which indicates if it is apb or ahb
> + bus respectively.
> +
> +What: /sys/kernel/debug/dcc/.../config_write
> +Date: March 2022
> +Contact: Souradeep Chowdhury <quic_schowdhu at quicinc.com>
> +Description:
> + This file allows user to write a value to the register
> + address given as argument. The reason for this feature
> + of dcc is that for accessing certain registers it is
> + necessary to set some bits of some other register.
> + Example:
> + echo <1> <2> <3> > /sys/bus/platform/devices/.../config_write
> + 1->Address to be considered for writing the value.
> + 2->The value that needs to be written at the location.
> + 3->Can be a 1 or 0 which indicates if it is apb or ahb
> + bus respectively.
> +
> +What: /sys/kernel/debug/dcc/.../config_reset
> +Date: March 2022
> +Contact: Souradeep Chowdhury <quic_schowdhu at quicinc.com>
> +Description:
> + This file is used to reset the configuration of
> + a dcc driver to the default configuration. This
> + means that all the previous addresses stored in
> + the driver gets removed and user needs to enter
> + the address values from the start.
> + Example:
> + echo 1 > /sys/bus/platform/devices/.../config_reset
> +
> +What: /sys/kernel/debug/dcc/.../config_loop
> +Date: March 2022
> +Contact: Souradeep Chowdhury <quic_schowdhu at quicinc.com>
> +Description:
> + This file is used to enter the loop type addresses for
> + dcc. DCC hardware provides feature to loop among multiple
> + addresses. For debugging purposes register values need to
> + be captured repeatedly in a loop. On giving the loop count
> + as n, the value at address will be captured n times in a
> + loop. At most 8 loop addresses can be configured at once.
> + Example:
> + echo <1> <2> <3> > /sys/kernel/debug/dcc/../config_loop
> + 1->The loop count, the number of times the value of the
> + addresses will be captured.
> + 2->The address count, total number of addresses to be
> + entered in this instruction.
> + 3->The series of addresses to be entered separated by a
> + space like <addr1> <addr2>... and so on.
> +
> +What: /sys/kernel/debug/dcc/.../config_read_write
> +Date: March 2022
> +Contact: Souradeep Chowdhury <quic_schowdhu at quicinc.com>
> +Description:
> + This file is used to read the value of the register
> + and then write the value given as an argument to the
> + register address. The address argument should be given
> + of the form <addr> <mask> <value>.For debugging purposes
> + sometimes we need to first read from a register and then
> + set some values to the register.
> + Example:
> + echo <1> <2> <3> > /sys/kernel/debug/dcc/.../config_read_write
> + 1->The address which needs to be considered for read then write.
> + 2->The value that needs to be written on the address.
> + 3->The mask of the value to be written.
> +
> +What: /sys/kernel/debug/dcc/.../ready
> +Date: March 2022
> +Contact Souradeep Chowdhury <quic_schowdhu at quicinc.com>
> +Description:
> + This file is used to check the status of the dcc
> + hardware if it's ready to take the inputs. A 0
> + here indicates dcc is in a ready condition.
> + Example:
> + cat /sys/kernel/debug/dcc/.../ready
> +
> +What: /sys/kernel/debug/dcc/.../curr_list
I still don't like the idea of having a single set of files to interface
with all N lists. I think you should discover how many lists you have
and create N directories of files, each on operating on a given list.
> +Date: March 2022
> +Contact: Souradeep Chowdhury <quic_schowdhu at quicinc.com>
> +Description:
> + This attribute is used to enter the linklist to be
> + used while appending addresses. The range of values
> + for this is advertised either by a register or is
> + predefined. Max value for this can be till 8.
> + Example:
> + echo 0 > /sys/kernel/debug/dcc/...curr_list
> +
Regards,
Bjorn
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