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 the MMIO based etm4x devices to be supported via 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.
The series applies on 6.3-rc4.
Changes in V2:
- Enables ACPI etm4x device support in the existing platform driver - Dropped last two patches from the series - Dropped redundant 'devarch' checking from is_etm4x_device() - Renamed updated is_etm4x_device() as is_etm4x_devtype() - Fixed arguments in fallback stub for etm4_check_arch_features() - Tagged etm4_dev_pm_ops with etm4_platform_driver - Updated the comment for coresight_get_enable_apb_pclk() helper - Updated the comment for new 'pclk' element in struct etm4_drvdata - Dropped the clock when devm_ioremap_resource() fails - Convert IS_ERR() into a direct pointer check in etm4_remove_platform_dev() - Dropped "arm,coresight-etm4x" compatible property from etm4_match[]
Changes in V1:
https://lore.kernel.org/all/20230317030501.1811905-1-anshuman.khandual@arm.c...
Cc: Steve Clevenger scclevenger@os.amperecomputing.com Cc: Rob Herring robh+dt@kernel.org Cc: Frank Rowand frowand.list@gmail.com Cc: Russell King (Oracle) linux@armlinux.org.uk Cc: Greg Kroah-Hartman gregkh@linuxfoundation.org Cc: "Rafael J. Wysocki" rafael@kernel.org Cc: Len Brown lenb@kernel.org Cc: Sudeep Holla sudeep.holla@arm.com Cc: Lorenzo Pieralisi lpieralisi@kernel.org Cc: Mathieu Poirier mathieu.poirier@linaro.org Cc: Suzuki K Poulose suzuki.poulose@arm.com Cc: Mike Leach mike.leach@linaro.org Cc: Leo Yan leo.yan@linaro.org Cc: devicetree@vger.kernel.org Cc: linux-acpi@vger.kernel.org Cc: coresight@lists.linaro.org Cc: linux-arm-kernel@lists.infradead.org Cc: linux-kernel@vger.kernel.org
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
Suzuki Poulose (1): coresight: etm4x: Add ACPI support in platform driver
drivers/acpi/acpi_amba.c | 1 - .../coresight/coresight-etm4x-core.c | 114 ++++++++++++++---- drivers/hwtracing/coresight/coresight-etm4x.h | 4 + include/linux/coresight.h | 59 +++++++++ 4 files changed, 154 insertions(+), 24 deletions(-)