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@xxxxxxxxxxx> > --- > 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@xxxxxxxxxxx> > +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@xxxxxxxxxxx> > +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@xxxxxxxxxxx> > +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@xxxxxxxxxxx> > +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@xxxxxxxxxxx> > +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@xxxxxxxxxxx> > +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@xxxxxxxxxxx> > +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@xxxxxxxxxxx> > +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@xxxxxxxxxxx> > +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
