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 <[email protected]>
Signed-off-by: Marc Zyngier <[email protected]>
Cc: Daniel Palmer <[email protected]>
Cc: Romain Perier <[email protected]>
Cc: Bartosz Golaszewski <[email protected]>
Cc: Thierry Reding <[email protected]>
Cc: Jonathan Hunter <[email protected]>
Cc: Robert Richter <[email protected]>
Cc: Nobuhiro Iwamatsu <[email protected]>
Cc: Andy Gross <[email protected]>
Cc: Bjorn Andersson <[email protected]>
Acked-by: Bartosz Golaszewski <[email protected]>
Link: https://lore.kernel.org/r/[email protected]

1 files changed, 6 insertions, 9 deletions

diff --git a/drivers/gpio/gpio-thunderx.c b/drivers/gpio/gpio-thunderx.c
index 9f66deab46ea..e1dedbca0c85 100644
--- a/drivers/gpio/gpio-thunderx.c
+++ b/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,
-						      unsigned int parent_hwirq,
-						      unsigned int parent_type)
+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,