gpio: Remove dynamic allocation from populate_parent_alloc_arg()

The gpiolib is unique in the way it uses intermediate fwspecs
when feeding an interrupt specifier to the parent domain, as it
relies on the populate_parent_alloc_arg() callback to perform
a dynamic allocation.

This is pretty inefficient (we free the structure almost immediately),
and the only reason this isn't a stack allocation is that our
ThunderX friend uses MSIs rather than a FW-constructed structure.

Let's solve it by providing a new type composed of the union
of a struct irq_fwspec and a msi_info_t, which satisfies both
requirements. This allows us to use a stack allocation, and we
can move the handful of users to this new scheme.

Also perform some additional cleanup, such as getting rid of the
stub versions of the irq_domain_translate_*cell helpers, which
are never used when CONFIG_IRQ_DOMAIN_HIERARCHY isn't selected.

Tested on a Tegra186.
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Cc: Daniel Palmer <daniel@thingy.jp>
Cc: Romain Perier <romain.perier@gmail.com>
Cc: Bartosz Golaszewski <brgl@bgdev.pl>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Jonathan Hunter <jonathanh@nvidia.com>
Cc: Robert Richter <rric@kernel.org>
Cc: Nobuhiro Iwamatsu <nobuhiro1.iwamatsu@toshiba.co.jp>
Cc: Andy Gross <agross@kernel.org>
Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Bartosz Golaszewski <brgl@bgdev.pl>
Link: https://lore.kernel.org/r/20220707182314.66610-2-prabhakar.mahadev-lad.rj@bp.renesas.com

drivers/gpio/gpio-msc313.c

@@ -550,15 +550,12 @@ static struct irq_chip msc313_gpio_irqchip = {
  * so we need to provide the fwspec. Essentially gpiochip_populate_parent_fwspec_twocell
  * that puts GIC_SPI into the first cell.
  */
-static void *msc313_gpio_populate_parent_fwspec(struct gpio_chip *gc,
+static int msc313_gpio_populate_parent_fwspec(struct gpio_chip *gc,
+					      union gpio_irq_fwspec *gfwspec,
 					      unsigned int parent_hwirq,
 					      unsigned int parent_type)
 {
-	struct irq_fwspec *fwspec;
-
-	fwspec = kmalloc(sizeof(*fwspec), GFP_KERNEL);
-	if (!fwspec)
-		return NULL;
+	struct irq_fwspec *fwspec = &gfwspec->fwspec;
 
 	fwspec->fwnode = gc->irq.parent_domain->fwnode;
 	fwspec->param_count = 3;
@@ -566,7 +563,7 @@ static void *msc313_gpio_populate_parent_fwspec(struct gpio_chip *gc,
 	fwspec->param[1] = parent_hwirq;
 	fwspec->param[2] = parent_type;
 
-	return fwspec;
+	return 0;
 }
 
 static int msc313e_gpio_child_to_parent_hwirq(struct gpio_chip *chip,

drivers/gpio/gpio-tegra.c

@@ -443,15 +443,12 @@ static int tegra_gpio_child_to_parent_hwirq(struct gpio_chip *chip,
 	return 0;
 }
 
-static void *tegra_gpio_populate_parent_fwspec(struct gpio_chip *chip,
+static int tegra_gpio_populate_parent_fwspec(struct gpio_chip *chip,
+					     union gpio_irq_fwspec *gfwspec,
 					     unsigned int parent_hwirq,
 					     unsigned int parent_type)
 {
-	struct irq_fwspec *fwspec;
-
-	fwspec = kmalloc(sizeof(*fwspec), GFP_KERNEL);
-	if (!fwspec)
-		return NULL;
+	struct irq_fwspec *fwspec = &gfwspec->fwspec;
 
 	fwspec->fwnode = chip->irq.parent_domain->fwnode;
 	fwspec->param_count = 3;
@@ -459,7 +456,7 @@ static void *tegra_gpio_populate_parent_fwspec(struct gpio_chip *chip,
 	fwspec->param[1] = parent_hwirq;
 	fwspec->param[2] = parent_type;
 
-	return fwspec;
+	return 0;
 }
 
 #ifdef CONFIG_PM_SLEEP

drivers/gpio/gpio-tegra186.c

@@ -621,16 +621,13 @@ static int tegra186_gpio_irq_domain_translate(struct irq_domain *domain,
 	return 0;
 }
 
-static void *tegra186_gpio_populate_parent_fwspec(struct gpio_chip *chip,
+static int tegra186_gpio_populate_parent_fwspec(struct gpio_chip *chip,
+						union gpio_irq_fwspec *gfwspec,
 						unsigned int parent_hwirq,
 						unsigned int parent_type)
 {
 	struct tegra_gpio *gpio = gpiochip_get_data(chip);
-	struct irq_fwspec *fwspec;
-
-	fwspec = kmalloc(sizeof(*fwspec), GFP_KERNEL);
-	if (!fwspec)
-		return NULL;
+	struct irq_fwspec *fwspec = &gfwspec->fwspec;
 
 	fwspec->fwnode = chip->irq.parent_domain->fwnode;
 	fwspec->param_count = 3;
@@ -638,7 +635,7 @@ static void *tegra186_gpio_populate_parent_fwspec(struct gpio_chip *chip,
 	fwspec->param[1] = parent_hwirq;
 	fwspec->param[2] = parent_type;
 
-	return fwspec;
+	return 0;
 }
 
 static int tegra186_gpio_child_to_parent_hwirq(struct gpio_chip *chip,

drivers/gpio/gpio-thunderx.c

@@ -408,18 +408,15 @@ static int thunderx_gpio_child_to_parent_hwirq(struct gpio_chip *gc,
 	return 0;
 }
 
-static void *thunderx_gpio_populate_parent_alloc_info(struct gpio_chip *chip,
+static int thunderx_gpio_populate_parent_alloc_info(struct gpio_chip *chip,
+						    union gpio_irq_fwspec *gfwspec,
 						    unsigned int parent_hwirq,
 						    unsigned int parent_type)
 {
-	msi_alloc_info_t *info;
-
-	info = kmalloc(sizeof(*info), GFP_KERNEL);
-	if (!info)
-		return NULL;
+	msi_alloc_info_t *info = &gfwspec->msiinfo;
 
 	info->hwirq = parent_hwirq;
-	return info;
+	return 0;
 }
 
 static int thunderx_gpio_probe(struct pci_dev *pdev,

drivers/gpio/gpio-visconti.c

@@ -103,15 +103,12 @@ static int visconti_gpio_child_to_parent_hwirq(struct gpio_chip *gc,
 	return -EINVAL;
 }
 
-static void *visconti_gpio_populate_parent_fwspec(struct gpio_chip *chip,
+static int visconti_gpio_populate_parent_fwspec(struct gpio_chip *chip,
+						union gpio_irq_fwspec *gfwspec,
 						unsigned int parent_hwirq,
 						unsigned int parent_type)
 {
-	struct irq_fwspec *fwspec;
-
-	fwspec = kmalloc(sizeof(*fwspec), GFP_KERNEL);
-	if (!fwspec)
-		return NULL;
+	struct irq_fwspec *fwspec = &gfwspec->fwspec;
 
 	fwspec->fwnode = chip->irq.parent_domain->fwnode;
 	fwspec->param_count = 3;
@@ -119,7 +116,7 @@ static void *visconti_gpio_populate_parent_fwspec(struct gpio_chip *chip,
 	fwspec->param[1] = parent_hwirq;
 	fwspec->param[2] = parent_type;
 
-	return fwspec;
+	return 0;
 }
 
 static int visconti_gpio_probe(struct platform_device *pdev)

drivers/gpio/gpiolib.c

@@ -1107,7 +1107,7 @@ static int gpiochip_hierarchy_irq_domain_alloc(struct irq_domain *d,
 	irq_hw_number_t hwirq;
 	unsigned int type = IRQ_TYPE_NONE;
 	struct irq_fwspec *fwspec = data;
-	void *parent_arg;
+	union gpio_irq_fwspec gpio_parent_fwspec = {};
 	unsigned int parent_hwirq;
 	unsigned int parent_type;
 	struct gpio_irq_chip *girq = &gc->irq;
@@ -1147,14 +1147,15 @@ static int gpiochip_hierarchy_irq_domain_alloc(struct irq_domain *d,
 	irq_set_probe(irq);
 
 	/* This parent only handles asserted level IRQs */
-	parent_arg = girq->populate_parent_alloc_arg(gc, parent_hwirq, parent_type);
-	if (!parent_arg)
-		return -ENOMEM;
+	ret = girq->populate_parent_alloc_arg(gc, &gpio_parent_fwspec,
+					      parent_hwirq, parent_type);
+	if (ret)
+		return ret;
 
 	chip_dbg(gc, "alloc_irqs_parent for %d parent hwirq %d\n",
 		  irq, parent_hwirq);
 	irq_set_lockdep_class(irq, gc->irq.lock_key, gc->irq.request_key);
-	ret = irq_domain_alloc_irqs_parent(d, irq, 1, parent_arg);
+	ret = irq_domain_alloc_irqs_parent(d, irq, 1, &gpio_parent_fwspec);
 	/*
 	 * If the parent irqdomain is msi, the interrupts have already
 	 * been allocated, so the EEXIST is good.
@@ -1166,7 +1167,6 @@ static int gpiochip_hierarchy_irq_domain_alloc(struct irq_domain *d,
 			 "failed to allocate parent hwirq %d for hwirq %lu\n",
 			 parent_hwirq, hwirq);
 
-	kfree(parent_arg);
 	return ret;
 }
 
@@ -1230,34 +1230,28 @@ static bool gpiochip_hierarchy_is_hierarchical(struct gpio_chip *gc)
 	return !!gc->irq.parent_domain;
 }
 
-void *gpiochip_populate_parent_fwspec_twocell(struct gpio_chip *gc,
+int gpiochip_populate_parent_fwspec_twocell(struct gpio_chip *gc,
+					    union gpio_irq_fwspec *gfwspec,
 					    unsigned int parent_hwirq,
 					    unsigned int parent_type)
 {
-	struct irq_fwspec *fwspec;
-
-	fwspec = kmalloc(sizeof(*fwspec), GFP_KERNEL);
-	if (!fwspec)
-		return NULL;
+	struct irq_fwspec *fwspec = &gfwspec->fwspec;
 
 	fwspec->fwnode = gc->irq.parent_domain->fwnode;
 	fwspec->param_count = 2;
 	fwspec->param[0] = parent_hwirq;
 	fwspec->param[1] = parent_type;
 
-	return fwspec;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(gpiochip_populate_parent_fwspec_twocell);
 
-void *gpiochip_populate_parent_fwspec_fourcell(struct gpio_chip *gc,
+int gpiochip_populate_parent_fwspec_fourcell(struct gpio_chip *gc,
+					     union gpio_irq_fwspec *gfwspec,
 					     unsigned int parent_hwirq,
 					     unsigned int parent_type)
 {
-	struct irq_fwspec *fwspec;
-
-	fwspec = kmalloc(sizeof(*fwspec), GFP_KERNEL);
-	if (!fwspec)
-		return NULL;
+	struct irq_fwspec *fwspec = &gfwspec->fwspec;
 
 	fwspec->fwnode = gc->irq.parent_domain->fwnode;
 	fwspec->param_count = 4;
@@ -1266,7 +1260,7 @@ void *gpiochip_populate_parent_fwspec_fourcell(struct gpio_chip *gc,
 	fwspec->param[2] = 0;
 	fwspec->param[3] = parent_type;
 
-	return fwspec;
+	return 0;
 }
 EXPORT_SYMBOL_GPL(gpiochip_populate_parent_fwspec_fourcell);
 

drivers/pinctrl/qcom/pinctrl-spmi-gpio.c

@@ -966,16 +966,13 @@ static int pmic_gpio_child_to_parent_hwirq(struct gpio_chip *chip,
 	return 0;
 }
 
-static void *pmic_gpio_populate_parent_fwspec(struct gpio_chip *chip,
+static int pmic_gpio_populate_parent_fwspec(struct gpio_chip *chip,
+					    union gpio_irq_fwspec *gfwspec,
 					    unsigned int parent_hwirq,
 					    unsigned int parent_type)
 {
 	struct pmic_gpio_state *state = gpiochip_get_data(chip);
-	struct irq_fwspec *fwspec;
-
-	fwspec = kzalloc(sizeof(*fwspec), GFP_KERNEL);
-	if (!fwspec)
-		return NULL;
+	struct irq_fwspec *fwspec = &gfwspec->fwspec;
 
 	fwspec->fwnode = chip->irq.parent_domain->fwnode;
 
@@ -985,7 +982,7 @@ static void *pmic_gpio_populate_parent_fwspec(struct gpio_chip *chip,
 	/* param[2] must be left as 0 */
 	fwspec->param[3] = parent_type;
 
-	return fwspec;
+	return 0;
 }
 
 static int pmic_gpio_probe(struct platform_device *pdev)

include/linux/gpio/driver.h

@@ -12,6 +12,8 @@
 #include <linux/property.h>
 #include <linux/types.h>
 
+#include <asm/msi.h>
+
 struct gpio_desc;
 struct of_phandle_args;
 struct device_node;
@@ -23,6 +25,13 @@ enum gpio_lookup_flags;
 
 struct gpio_chip;
 
+union gpio_irq_fwspec {
+	struct irq_fwspec	fwspec;
+#ifdef CONFIG_GENERIC_MSI_IRQ_DOMAIN
+	msi_alloc_info_t	msiinfo;
+#endif
+};
+
 #define GPIO_LINE_DIRECTION_IN	1
 #define GPIO_LINE_DIRECTION_OUT	0
 
@@ -103,7 +112,8 @@ struct gpio_irq_chip {
 	 * variant named &gpiochip_populate_parent_fwspec_fourcell is also
 	 * available.
 	 */
-	void *(*populate_parent_alloc_arg)(struct gpio_chip *gc,
+	int (*populate_parent_alloc_arg)(struct gpio_chip *gc,
+					 union gpio_irq_fwspec *fwspec,
 					 unsigned int parent_hwirq,
 					 unsigned int parent_type);
 
@@ -646,29 +656,15 @@ struct bgpio_pdata {
 
 #ifdef CONFIG_IRQ_DOMAIN_HIERARCHY
 
-void *gpiochip_populate_parent_fwspec_twocell(struct gpio_chip *gc,
+int gpiochip_populate_parent_fwspec_twocell(struct gpio_chip *gc,
+					    union gpio_irq_fwspec *gfwspec,
 					    unsigned int parent_hwirq,
 					    unsigned int parent_type);
-void *gpiochip_populate_parent_fwspec_fourcell(struct gpio_chip *gc,
+int gpiochip_populate_parent_fwspec_fourcell(struct gpio_chip *gc,
+					     union gpio_irq_fwspec *gfwspec,
 					     unsigned int parent_hwirq,
 					     unsigned int parent_type);
 
-#else
-
-static inline void *gpiochip_populate_parent_fwspec_twocell(struct gpio_chip *gc,
-						    unsigned int parent_hwirq,
-						    unsigned int parent_type)
-{
-	return NULL;
-}
-
-static inline void *gpiochip_populate_parent_fwspec_fourcell(struct gpio_chip *gc,
-						     unsigned int parent_hwirq,
-						     unsigned int parent_type)
-{
-	return NULL;
-}
-
 #endif /* CONFIG_IRQ_DOMAIN_HIERARCHY */
 
 int bgpio_init(struct gpio_chip *gc, struct device *dev,