From e24328974a88aa8541e94e8bb8dfa2ade1b3c45d Mon Sep 17 00:00:00 2001 From: Donggeun Yoo Date: Wed, 2 Sep 2026 00:21:26 +0900 Subject: iio: proximity: vl53l0x-i2c: claim direct mode for raw reads vl53l0x_read_raw() starts a single-shot ranging measurement and reads back the result. Once the triggered buffer is enabled the sensor runs in continuous mode and its data-ready interrupt is routed to the trigger, so a concurrent in_distance_raw read disturbs the streaming setup and never gets its completion, returning -ETIMEDOUT. The original submission claimed direct mode here, but it was dropped during review because the driver had no buffer support at the time [1]. Continuous (buffered) mode was later added without restoring the claim [2], reintroducing the conflict. Reject direct reads while buffered capture is active by claiming direct mode around the measurement, as the vl53l1x sibling already does. Fixes: 762186c6e7b1 ("iio: proximity: vl53l0x-i2c: Added continuous mode support") Link: https://lore.kernel.org/linux-iio/20180911160300.GA9212@himanshu-Vostro-3559/ [1] Link: https://lore.kernel.org/linux-iio/20240909101508.263085-3-abhashkumarjha123@gmail.com/ [2] Signed-off-by: Donggeun Yoo Cc: stable@vger.kernel.org Signed-off-by: Jonathan Cameron --- Documentation/PCI/tph.rst | 132 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 132 insertions(+) create mode 100644 Documentation/PCI/tph.rst (limited to 'Documentation/PCI/tph.rst') diff --git a/Documentation/PCI/tph.rst b/Documentation/PCI/tph.rst new file mode 100644 index 000000000..b6cf22b9b --- /dev/null +++ b/Documentation/PCI/tph.rst @@ -0,0 +1,132 @@ +.. SPDX-License-Identifier: GPL-2.0 + + +=========== +TPH Support +=========== + +:Copyright: 2024 Advanced Micro Devices, Inc. +:Authors: - Eric van Tassell + - Wei Huang + + +Overview +======== + +TPH (TLP Processing Hints) is a PCIe feature that allows endpoint devices +to provide optimization hints for requests that target memory space. +These hints, in a format called Steering Tags (STs), are embedded in the +requester's TLP headers, enabling the system hardware, such as the Root +Complex, to better manage platform resources for these requests. + +For example, on platforms with TPH-based direct data cache injection +support, an endpoint device can include appropriate STs in its DMA +traffic to specify which cache the data should be written to. This allows +the CPU core to have a higher probability of getting data from cache, +potentially improving performance and reducing latency in data +processing. + + +How to Use TPH +============== + +TPH is presented as an optional extended capability in PCIe. The Linux +kernel handles TPH discovery during boot, but it is up to the device +driver to request TPH enablement if it is to be utilized. Once enabled, +the driver uses the provided API to obtain the Steering Tag for the +target memory and to program the ST into the device's ST table. + +Enable TPH support in Linux +--------------------------- + +To support TPH, the kernel must be built with the CONFIG_PCIE_TPH option +enabled. + +Manage TPH +---------- + +To enable TPH for a device, use the following function:: + + int pcie_enable_tph(struct pci_dev *pdev, int mode); + +This function enables TPH support for device with a specific ST mode. +Current supported modes include: + + * PCI_TPH_ST_NS_MODE - NO ST Mode + * PCI_TPH_ST_IV_MODE - Interrupt Vector Mode + * PCI_TPH_ST_DS_MODE - Device Specific Mode + +`pcie_enable_tph()` checks whether the requested mode is actually +supported by the device before enabling. The device driver can figure out +which TPH mode is supported and can be properly enabled based on the +return value of `pcie_enable_tph()`. + +To disable TPH, use the following function:: + + void pcie_disable_tph(struct pci_dev *pdev); + +Manage ST +--------- + +Steering Tags are platform specific. PCIe spec does not specify where STs +are from. Instead PCI Firmware Specification defines an ACPI _DSM method +(see the `Revised _DSM for Cache Locality TPH Features ECN +`_) for retrieving +STs for a target memory of various properties. This method is what is +supported in this implementation. + +To retrieve a Steering Tag for a target memory associated with a specific +CPU, use the following function:: + + int pcie_tph_get_cpu_st(struct pci_dev *pdev, enum tph_mem_type type, + unsigned int cpu, u16 *tag); + +The `type` argument is used to specify the memory type, either volatile +or persistent, of the target memory. The `cpu` argument specifies the +CPU where the memory is associated to. + +After the ST value is retrieved, the device driver can use the following +function to write the ST into the device:: + + int pcie_tph_set_st_entry(struct pci_dev *pdev, unsigned int index, + u16 tag); + +The `index` argument is the ST table entry index the ST tag will be +written into. `pcie_tph_set_st_entry()` will figure out the proper +location of ST table, either in the MSI-X table or in the TPH Extended +Capability space, and write the Steering Tag into the ST entry pointed by +the `index` argument. + +It is completely up to the driver to decide how to use these TPH +functions. For example a network device driver can use the TPH APIs above +to update the Steering Tag when interrupt affinity of a RX/TX queue has +been changed. Here is a sample code for IRQ affinity notifier: + +.. code-block:: c + + static void irq_affinity_notified(struct irq_affinity_notify *notify, + const cpumask_t *mask) + { + struct drv_irq *irq; + unsigned int cpu_id; + u16 tag; + + irq = container_of(notify, struct drv_irq, affinity_notify); + cpumask_copy(irq->cpu_mask, mask); + + /* Pick a right CPU as the target - here is just an example */ + cpu_id = cpumask_first(irq->cpu_mask); + + if (pcie_tph_get_cpu_st(irq->pdev, TPH_MEM_TYPE_VM, cpu_id, + &tag)) + return; + + if (pcie_tph_set_st_entry(irq->pdev, irq->msix_nr, tag)) + return; + } + +Disable TPH system-wide +----------------------- + +There is a kernel command line option available to control TPH feature: + * "notph": TPH will be disabled for all endpoint devices. -- cgit v1.3.1