Merge tag 'gpio-updates-for-v7.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/brgl/linux

Pull gpio updates from Bartosz Golaszewski:
 "There are two new drivers and some changes to GPIO core but mostly
  just GPIO driver updates across a wide array of files, adding support
  for new models as well as various refactoring changes. Nothing
  controversial and everything has spent a good measure of time in
  linux-next.

  GPIOLIB core:
   - shrink the GPIO bus driver stub code
   - rework software node support for "undefined" software nodes
   - provide and use devm_fwnode_gpiod_get_optional()
   - only compile the OF quirk for MT2701 when needed

  New drivers:
   - add the GPIO driver for ROHM bd72720
   - add the gpio-line-mux driver providing 1-to-many mapping for a
     single real GPIO

  Driver changes:
   - refactor gpio-pca9570: use lock guard, add missing headers, use
     devres consistently
   - add support for a new model (G7 Aspeed sgpiom) to the aspeed-sgpio
     driver along with some prerequisite refactoring
   - use device_get_match_data() where applicable and save some lines
   - add support for more models to gpio-cadence
   - add the compatible property to reset-gpio and use it in shared GPIO
     management
   - drop unnecessary use of irqd_get_trigger_type() in gpio-max77759
   - add support for a new variant to gpio-pca953x
   - extend build coverage with COMPILE_TEST for more drivers
   - constify configfs structures in gpio-sim and gpio-virtuser
   - add support for the K3 SoC to gpio-spacemit
   - implement the missing .get_direction() callback in gpio-max77620
   - add support for Tegra264 to gpio-tegra186
   - drop unneeded MODULE_ALIAS() from gpio-menz127

  DT bindings:
   - document support for the opencores GPIO controller in gpio-mmio
   - document new variants for gpio-pca953x

  Documentation:
   - extensively describe interrupt source detection for gpio-pca953x
     and add more models to the list of supported variants"

* tag 'gpio-updates-for-v7.0-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/brgl/linux: (59 commits)
  gpio: tegra186: Add support for Tegra264
  dt-bindings: gpio: Add Tegra264 support
  gpio: spacemit-k1: Use PDR for pin direction, not SDR/CDR
  gpio: max77620: Implement .get_direction() callback
  gpio: aspeed-sgpio: Support G7 Aspeed sgpiom controller
  dt-bindings: gpio: aspeed,sgpio: Support ast2700
  gpio: aspeed-sgpio: Convert IRQ functions to use llops callbacks
  gpio: aspeed-sgpio: Create llops to handle hardware access
  gpio: aspeed-sgpio: Remove unused bank name field
  gpio: aspeed-sgpio: Change the macro to support deferred probe
  regulator: bd71815: switch to devm_fwnode_gpiod_get_optional
  gpiolib: introduce devm_fwnode_gpiod_get_optional() wrapper
  gpio: mmio: Add compatible for opencores GPIO
  dt-bindings: gpio-mmio: Correct opencores GPIO
  gpio: pca9570: use lock guards
  gpio: pca9570: Don't use "proxy" headers
  gpio: pca9570: Use devm_mutex_init() for mutex initialization
  MAINTAINERS: Add ROHM BD72720 PMIC
  power: supply: bd71828-power: Support ROHM BD72720
  power: supply: bd71828: Support wider register addresses
  ...

1 files changed, 87 insertions, 0 deletions

diff --git a/Documentation/driver-api/gpio/pca953x.rst b/Documentation/driver-api/gpio/pca953x.rst
index 4bd7cf1120cb..fa4a57aa82a7 100644
--- a/Documentation/driver-api/gpio/pca953x.rst
+++ b/Documentation/driver-api/gpio/pca953x.rst
@@ -178,6 +178,8 @@ pcal9554b      8       yes    00     01     02        03
 pcal6416      16       yes    00     02     04        06
 pcal9535      16       yes    00     02     04        06
 pcal9555a     16       yes    00     02     04        06
+tcal6408       8       yes    00     01     02        03
+tcal6416      16       yes    00     02     04        06
 ========== ===== ========= ===== ====== ====== =========
 
 These chips have several additional features:
@@ -196,6 +198,8 @@ pcal9554b            40       42      43       44       45         46       4F
 pcal6416             40       44      46       48       4A         4C       4F
 pcal9535             40       44      46       48       4A         4C       4F
 pcal9555a            40       44      46       48       4A         4C       4F
+tcal6408             40       42      43       44       45         46       4F
+tcal6416             40       44      46       48       4A         4C       4F
 ========== ============ ======== ======= ======== ======== ========== ========
 
 Currently the driver has support for the input latch, pull-up/pull-down
@@ -332,6 +336,8 @@ Layouts:
         - pcal9554b
         - pcal9555a
         - pcal6524
+        - tcal6408
+        - tcal6416
 
     2. base offset 0x30, bank 5 and 6, closely packed banks
         - pcal6534
@@ -383,6 +389,13 @@ disabled.
 Currently the driver enables the latch for each line with interrupt
 enabled.
 
+An interrupt status register records which pins triggered an interrupt.
+However, the status register and the input port register must be read
+separately; there is no atomic mechanism to read both simultaneously, so races
+are possible. Refer to the chapter `Interrupt source detection`_ to understand
+the implications of this and how the driver still makes use of the latching
+feature.
+
     1. base offset 0x40, bank 2, bank offsets of 2^n
         - pcal6408
         - pcal6416
@@ -390,6 +403,8 @@ enabled.
         - pcal9554b
         - pcal9555a
         - pcal6524
+        - tcal6408
+        - tcal6416
 
     2. base offset 0x30, bank 2, closely packed banks
         - pcal6534
@@ -462,6 +477,8 @@ Layout:
         - pcal9535
         - pcal9554b
         - pcal9555a
+        - tcal6408
+        - tcal6416
 
 `PCAL chips with extended interrupt and output configuration functions`_
 can set this for each line individually. They have the same per-port out_conf
@@ -505,12 +522,82 @@ bits drive strength
         - pcal9554b
         - pcal9555a
         - pcal6524
+        - tcal6408
+        - tcal6416
 
     2. base offset 0x30, bank 0 and 1, closely packed banks
         - pcal6534
 
 Currently not supported by the driver.
 
+Interrupt source detection
+==========================
+
+When triggered by the GPIO expander's interrupt, the driver determines which
+IRQs are pending by reading the input port register.
+
+To be able to filter on specific interrupt events for all compatible devices,
+the driver keeps track of the previous input state of the lines, and emits an
+IRQ only for the correct edge or level. This system works irrespective of the
+number of enabled interrupts. Events will not be missed even if they occur
+between the GPIO expander's interrupt and the actual I2C read. Edges could of
+course be missed if the related signal level changes back to the value
+previously saved by the driver before the I2C read. PCAL variants offer input
+latching for that reason.
+
+PCAL input latching
+-------------------
+
+The PCAL variants have an input latch and the driver enables this for all
+interrupt-enabled lines. The interrupt is then only cleared when the input port
+is read out. These variants provide an interrupt status register that records
+which pins triggered an interrupt, but the status and input registers cannot be
+read atomically. If another interrupt occurs on a different line after the
+status register has been read but before the input port register is sampled,
+that event will not be reflected in the earlier status snapshot, so relying
+solely on the interrupt status register is insufficient.
+
+Thus, the PCAL variants also have to use the existing level-change logic.
+
+For short pulses, the first edge is captured when the input register is read,
+but if the signal returns to its previous level before this read, the second
+edge is not observed. As a result, successive pulses can produce identical
+input values at read time and no level change is detected, causing interrupts
+to be missed. Below timing diagram shows this situation where the top signal is
+the input pin level and the bottom signal indicates the latched value::
+
+  ─────┐     ┌──*───────────────┐     ┌──*─────────────────┐     ┌──*───
+       │     │  .               │     │  .                 │     │  .
+       │     │  │               │     │  │                 │     │  │
+       └──*──┘  │               └──*──┘  │                 └──*──┘  │
+  Input   │     │                  │     │                    │     │
+          ▼     │                  ▼     │                    ▼     │
+         IRQ    │                 IRQ    │                   IRQ    │
+                .                        .                          .
+  ─────┐        .┌──────────────┐        .┌────────────────┐        .┌──
+       │         │              │         │                │         │
+       │         │              │         │                │         │
+       └────────*┘              └────────*┘                └────────*┘
+  Latched       │                        │                          │
+                ▼                        ▼                          ▼
+              READ 0                   READ 0                     READ 0
+                                     NO CHANGE                  NO CHANGE
+
+To deal with this, events indicated by the interrupt status register are merged
+with events detected through the existing level-change logic. As a result:
+
+- short pulses, whose second edges are invisible, are detected via the
+  interrupt status register, and
+- interrupts that occur between the status and input reads are still
+  caught by the generic level-change logic.
+
+Note that this is still best-effort: the status and input registers are read
+separately, and short pulses on other lines may occur in between those reads.
+Such pulses can still be latched as an interrupt without leaving an observable
+level change at read time, and may not be attributable to a specific edge. This
+does not reduce detection compared to the generic path, but reflects inherent
+atomicity limitations.
+
 Datasheets
 ==========