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+From fc23ea48ba52c24f201fe5ca0132ee1a3de5a70a Mon Sep 17 00:00:00 2001
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+From: Mauri Sandberg <[email protected]>
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+Date: Thu, 25 Mar 2021 11:48:05 +0200
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+Subject: [PATCH 2/2] gpio: gpio-cascade: add generic GPIO cascade
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+Adds support for building cascades of GPIO lines. That is, it allows
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+setups when there is one upstream line and multiple cascaded lines, out
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+of which one can be chosen at a time. The status of the upstream line
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+can be conveyed to the selected cascaded line or, vice versa, the status
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+of the cascaded line can be conveyed to the upstream line.
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+
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+A multiplexer is being used to select, which cascaded GPIO line is being
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+used at any given time.
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+
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+At the moment only input direction is supported. In future it should be
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+possible to add support for output direction, too.
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+
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+Signed-off-by: Mauri Sandberg <[email protected]>
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+Reviewed-by: Linus Walleij <[email protected]>
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+Reviewed-by: Andy Shevchenko <[email protected]>
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+---
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+v7 -> v8:
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+ - rearrange members in struct gpio_cascade
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+ - cosmetic changes in file header and in one function declaration
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+ - added Reviewed-by tags by Linus and Andy
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+v6 -> v7:
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+ - In Kconfig add info about module name
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+ - adhere to new convention that allows lines longer than 80 chars
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+ - use dev_probe_err with upstream gpio line too
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+ - refactor for cleaner exit of probe function.
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+v5 -> v6:
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+ - In Kconfig, remove dependency to OF_GPIO and select only MULTIPLEXER
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+ - refactor code preferring one-liners
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+ - clean up prints, removing them from success-path.
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+ - don't explicitly set gpio_chip.of_node as it's done in the GPIO library
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+ - use devm_gpiochip_add_data instead of gpiochip_add
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+v4 -> v5:
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+ - renamed gpio-mux-input -> gpio-cascade. refactored code accordingly
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+ here and there and changed to use new bindings and compatible string
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+ - ambigious and vague 'pin' was rename to 'upstream_line'
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+ - dropped Tested-by and Reviewed-by due to changes in bindings
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+ - dropped Reported-by suggested by an automatic bot as it was not really
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+ appropriate to begin with
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+ - functionally it's the same as v4
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+v3 -> v4:
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+ - Changed author email
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+ - Included Tested-by and Reviewed-by from Drew
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+v2 -> v3:
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+ - use managed device resources
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+ - update Kconfig description
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+v1 -> v2:
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+ - removed .owner from platform_driver as per test bot's instruction
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+ - added MODULE_AUTHOR, MODULE_DESCRIPTION, MODULE_LICENSE
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+ - added gpio_mux_input_get_direction as it's recommended for all chips
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+ - removed because this is input only chip: gpio_mux_input_set_value
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+ - removed because they are not needed for input/output only chips:
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+ gpio_mux_input_direction_input
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+ gpio_mux_input_direction_output
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+ - fixed typo in an error message
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+ - added info message about successful registration
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+ - removed can_sleep flag as this does not sleep while getting GPIO value
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+ like I2C or SPI do
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+ - Updated description in Kconfig
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+---
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+ drivers/gpio/Kconfig | 15 +++++
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+ drivers/gpio/Makefile | 1 +
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+ drivers/gpio/gpio-cascade.c | 117 ++++++++++++++++++++++++++++++++++++
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+ 3 files changed, 133 insertions(+)
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+ create mode 100644 drivers/gpio/gpio-cascade.c
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+
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+diff --git a/drivers/gpio/Kconfig b/drivers/gpio/Kconfig
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+index 37a6f77c86fe..e69457144459 100644
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+--- a/drivers/gpio/Kconfig
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++++ b/drivers/gpio/Kconfig
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+@@ -1694,4 +1694,19 @@ config GPIO_VIRTIO
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+
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+ endmenu
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+
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++comment "Other GPIO expanders"
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++
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++config GPIO_CASCADE
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++ tristate "General GPIO cascade"
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++ select MULTIPLEXER
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++ help
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++ Say yes here to enable support for generic GPIO cascade.
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++
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++ This allows building one-to-many cascades of GPIO lines using
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++ different types of multiplexers readily available. At the
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++ moment only input lines are supported.
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++
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++ To build the driver as a module choose 'm' and the resulting module
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++ will be called 'gpio-cascade'.
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++
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+ endif
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+diff --git a/drivers/gpio/Makefile b/drivers/gpio/Makefile
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+index 71ee9fc2ff83..e8945456e7ea 100644
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+--- a/drivers/gpio/Makefile
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++++ b/drivers/gpio/Makefile
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+@@ -45,6 +45,7 @@ obj-$(CONFIG_GPIO_BD9571MWV) += gpio-bd9571mwv.o
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+ obj-$(CONFIG_GPIO_BRCMSTB) += gpio-brcmstb.o
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+ obj-$(CONFIG_GPIO_BT8XX) += gpio-bt8xx.o
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+ obj-$(CONFIG_GPIO_CADENCE) += gpio-cadence.o
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++obj-$(CONFIG_GPIO_CASCADE) += gpio-cascade.o
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+ obj-$(CONFIG_GPIO_CLPS711X) += gpio-clps711x.o
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+ obj-$(CONFIG_GPIO_SNPS_CREG) += gpio-creg-snps.o
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+ obj-$(CONFIG_GPIO_CRYSTAL_COVE) += gpio-crystalcove.o
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+diff --git a/drivers/gpio/gpio-cascade.c b/drivers/gpio/gpio-cascade.c
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+new file mode 100644
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+index 000000000000..5cbda882d79a
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+--- /dev/null
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++++ b/drivers/gpio/gpio-cascade.c
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+@@ -0,0 +1,117 @@
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++// SPDX-License-Identifier: GPL-2.0-only
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++/*
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++ * A generic GPIO cascade driver
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++ *
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++ * Copyright (C) 2021 Mauri Sandberg <[email protected]>
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++ *
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++ * This allows building cascades of GPIO lines in a manner illustrated
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++ * below:
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++ *
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++ * /|---- Cascaded GPIO line 0
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++ * Upstream | |---- Cascaded GPIO line 1
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++ * GPIO line ----+ | .
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++ * | | .
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++ * \|---- Cascaded GPIO line n
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++ *
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++ * A multiplexer is being used to select, which cascaded line is being
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++ * addressed at any given time.
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++ *
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++ * At the moment only input mode is supported due to lack of means for
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++ * testing output functionality. At least theoretically output should be
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++ * possible with open drain constructions.
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++ */
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++
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++#include <linux/module.h>
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++#include <linux/slab.h>
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++#include <linux/platform_device.h>
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++#include <linux/mux/consumer.h>
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++
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++#include <linux/gpio/consumer.h>
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++#include <linux/gpio/driver.h>
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++
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++struct gpio_cascade {
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++ struct gpio_chip gpio_chip;
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++ struct device *parent;
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++ struct mux_control *mux_control;
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++ struct gpio_desc *upstream_line;
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++};
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++
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++static struct gpio_cascade *chip_to_cascade(struct gpio_chip *gc)
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++{
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++ return container_of(gc, struct gpio_cascade, gpio_chip);
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++}
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++
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++static int gpio_cascade_get_direction(struct gpio_chip *gc, unsigned int offset)
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++{
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++ return GPIO_LINE_DIRECTION_IN;
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++}
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++
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++static int gpio_cascade_get_value(struct gpio_chip *gc, unsigned int offset)
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++{
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++ struct gpio_cascade *cas = chip_to_cascade(gc);
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++ int ret;
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++
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++ ret = mux_control_select(cas->mux_control, offset);
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++ if (ret)
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++ return ret;
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++
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++ ret = gpiod_get_value(cas->upstream_line);
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++ mux_control_deselect(cas->mux_control);
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++ return ret;
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++}
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++
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++static int gpio_cascade_probe(struct platform_device *pdev)
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++{
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++ struct device *dev = &pdev->dev;
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++ struct gpio_cascade *cas;
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++ struct mux_control *mc;
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++ struct gpio_desc *upstream;
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++ struct gpio_chip *gc;
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++
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++ cas = devm_kzalloc(dev, sizeof(*cas), GFP_KERNEL);
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++ if (!cas)
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++ return -ENOMEM;
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++
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++ mc = devm_mux_control_get(dev, NULL);
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++ if (IS_ERR(mc))
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++ return dev_err_probe(dev, PTR_ERR(mc), "unable to get mux-control\n");
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++
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++ cas->mux_control = mc;
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++ upstream = devm_gpiod_get(dev, "upstream", GPIOD_IN);
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++ if (IS_ERR(upstream))
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++ return dev_err_probe(dev, PTR_ERR(upstream), "unable to claim upstream GPIO line\n");
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++
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++ cas->upstream_line = upstream;
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++ cas->parent = dev;
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++
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++ gc = &cas->gpio_chip;
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++ gc->get = gpio_cascade_get_value;
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++ gc->get_direction = gpio_cascade_get_direction;
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++ gc->base = -1;
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++ gc->ngpio = mux_control_states(mc);
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++ gc->label = dev_name(cas->parent);
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++ gc->parent = cas->parent;
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++ gc->owner = THIS_MODULE;
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++
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++ platform_set_drvdata(pdev, cas);
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++ return devm_gpiochip_add_data(dev, &cas->gpio_chip, NULL);
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++}
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++
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++static const struct of_device_id gpio_cascade_id[] = {
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++ { .compatible = "gpio-cascade" },
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++ { /* sentinel */ }
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++};
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++MODULE_DEVICE_TABLE(of, gpio_cascade_id);
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++
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++static struct platform_driver gpio_cascade_driver = {
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++ .driver = {
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++ .name = "gpio-cascade",
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++ .of_match_table = gpio_cascade_id,
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++ },
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++ .probe = gpio_cascade_probe,
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++};
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++module_platform_driver(gpio_cascade_driver);
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++
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++MODULE_AUTHOR("Mauri Sandberg <[email protected]>");
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++MODULE_DESCRIPTION("Generic GPIO cascade");
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++MODULE_LICENSE("GPL");
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+--
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+2.25.1
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+
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Mauri Sandberg