CoreSight ETM4x devices could be accessed either via MMIO (handled via
amba_driver) or CPU system instructions (handled via platform driver). But
this has the following issues :
- Each new CPU comes up with its own PID and thus we need to keep on
adding the "known" PIDs to get it working with AMBA driver. While
the ETM4 architecture (and CoreSight architecture) defines way to
identify a device as ETM4. Thus older kernels won't be able to
"discover" a newer CPU, unless we add the PIDs.
- With ACPI, the ETM4x devices have the same HID to identify the device
irrespective of the mode of access. This creates a problem where two
different drivers (both AMBA based driver and platform driver) would
hook into the "HID" and could conflict. e.g., if AMBA driver gets
hold of a non-MMIO device, the probe fails. If we have single driver
hooked into the given "HID", we could handle them seamlessly,
irrespective of the mode of access.
- CoreSight is heavily dependent on the runtime power management. With
ACPI, amba_driver doesn't get us anywhere with handling the power
and thus one need to always turn the power ON to use them. Moving to
platform driver gives us the power management for free.
Due to all of the above, we are moving ACPI MMIO based etm4x devices to be
supported via tha platform driver. The series makes the existing platform
driver generic to handle both type of the access modes. Although existing
AMBA driver would still continue to support DT based etm4x MMIO devices.
Although some problems still remain, such as manually adding PIDs for all
new AMBA DT based devices.
Anshuman Khandual (4):
coresight: etm4x: Allocate and device assign 'struct etmv4_drvdata'
earlier
coresight: etm4x: Drop iomem 'base' argument from etm4_probe()
coresight: etm4x: Drop pid argument from etm4_probe()
coresight: etm4x: Change etm4_platform_driver driver for MMIO devices
Junhao He (1):
Revert "coresight: ete: Add acpi match id for Hip09"
Suzuki K Poulose (2):
coresight: platform: acpi: Ignore the absence of graph
coresight: etm4x: Add ACPI support in platform driver
drivers/acpi/acpi_amba.c | 1 -
.../coresight/coresight-etm4x-core.c | 119 ++++++++++++++----
drivers/hwtracing/coresight/coresight-etm4x.h | 4 +
.../hwtracing/coresight/coresight-platform.c | 6 +-
include/linux/coresight.h | 59 +++++++++
5 files changed, 162 insertions(+), 27 deletions(-)
--
2.33.0