of/irq: Support #msi-cells=<0> in of_msi_get_domain

An 'msi-parent' property with a single entry and no accompanying '#msi-cells' property is considered the legacy definition as opposed to its definition after being expanded with commit 126b16e2ad98 ("Docs: dt: add generic MSI bindings"). However, the legacy definition is completely compatible with the current definition and, since of_phandle_iterator_next() tolerates missing and present-but- zero *cells properties since commit e42ee61017f5 ("of: Let of_for_each_phandle fallback to non-negative cell_count"), there's no need anymore to special case the legacy definition in of_msi_get_domain().

Indeed, special casing has turned out to be harmful, because, as of commit 7c025238b47a ("dt-bindings: irqchip: Describe the IMX MU block as a MSI controller"), MSI controller DT bindings have started specifying '#msi-cells' as a required property (even when the value must be zero) as an effort to make the bindings more explicit. But, since the special casing of 'msi-parent' only uses the existence of '#msi-cells' for its heuristic, and not whether or not it's also nonzero, the legacy path is not taken. Furthermore, the path to support the new, broader definition isn't taken either since that path has been restricted to the platform-msi bus.

But, neither the definition of 'msi-parent' nor the definition of '#msi-cells' is platform-msi-specific (the platform-msi bus was just the first bus that needed '#msi-cells'), so remove both the special casing and the restriction. The code removal also requires changing to of_parse_phandle_with_optional_args() in order to ensure the legacy (but compatible) use of 'msi-parent' remains supported. This not only simplifies the code but also resolves an issue with PCI devices finding their MSI controllers on riscv, as the riscv,imsics binding requires '#msi-cells=<0>'.

Signed-off-by Andrew Jones <[email protected]>

---
v2:
- switch to of_parse_phandle_with_optional_args() to ensure the absence of #msi-cells means count=0

 drivers/of/irq.c | 37 +++++++++++--------------------------
 1 file changed, 11 insertions(+), 26 deletions(-)

drivers/of/irq.c +3 -9

index c94203ce65bb..690df4b71ab9 100644
@@ -709,8 +709,7 @@ struct irq_domain *of_msi_map_get_device_domain(struct device *dev, u32 id,
  * @np: device node for @dev
  * @token: bus type for this domain
  *
- * Parse the msi-parent property (both the simple and the complex
- * versions), and returns the corresponding MSI domain.
+ * Parse the msi-parent property and returns the corresponding MSI domain.
  *
  * Returns: the MSI domain for this device (or NULL on failure).
  */

@@ -718,33 +717,19 @@ struct irq_domain *of_msi_get_domain(struct device *dev,
                                     struct device_node *np,
                                     enum irq_domain_bus_token token)
 {
-       struct device_node *msi_np;
+       struct of_phandle_args args;
        struct irq_domain *d;
+       int index = 0;
 
-       /* Check for a single msi-parent property */
-       msi_np = of_parse_phandle(np, "msi-parent", 0);
-       if (msi_np && !of_property_read_bool(msi_np, "#msi-cells")) {
-               d = irq_find_matching_host(msi_np, token);
-               if (!d)
-                       of_node_put(msi_np);

Quoted 78 lines · Andrew Jones

An 'msi-parent' property with a single entry and no accompanying '#msi-cells' property is considered the legacy definition as opposed to its definition after being expanded with commit 126b16e2ad98 ("Docs: dt: add generic MSI bindings"). However, the legacy definition is completely compatible with the current definition and, since of_phandle_iterator_next() tolerates missing and present-but- zero *cells properties since commit e42ee61017f5 ("of: Let of_for_each_phandle fallback to non-negative cell_count"), there's no need anymore to special case the legacy definition in of_msi_get_domain().

Indeed, special casing has turned out to be harmful, because, as of commit 7c025238b47a ("dt-bindings: irqchip: Describe the IMX MU block as a MSI controller"), MSI controller DT bindings have started specifying '#msi-cells' as a required property (even when the value must be zero) as an effort to make the bindings more explicit. But, since the special casing of 'msi-parent' only uses the existence of '#msi-cells' for its heuristic, and not whether or not it's also nonzero, the legacy path is not taken. Furthermore, the path to support the new, broader definition isn't taken either since that path has been restricted to the platform-msi bus.

But, neither the definition of 'msi-parent' nor the definition of '#msi-cells' is platform-msi-specific (the platform-msi bus was just the first bus that needed '#msi-cells'), so remove both the special casing and the restriction. The code removal also requires changing to of_parse_phandle_with_optional_args() in order to ensure the legacy (but compatible) use of 'msi-parent' remains supported. This not only simplifies the code but also resolves an issue with PCI devices finding their MSI controllers on riscv, as the riscv,imsics binding requires '#msi-cells=<0>'.

Signed-off-by Andrew Jones <[email protected]>

---
v2:
- switch to of_parse_phandle_with_optional_args() to ensure the absence of #msi-cells means count=0

 drivers/of/irq.c | 37 +++++++++++--------------------------
 1 file changed, 11 insertions(+), 26 deletions(-)

drivers/of/irq.c +3 -16

index c94203ce65bb..690df4b71ab9 100644
@@ -709,8 +709,7 @@ struct irq_domain *of_msi_map_get_device_domain(struct device *dev, u32 id,
  * @np: device node for @dev
  * @token: bus type for this domain
  *
- * Parse the msi-parent property (both the simple and the complex
- * versions), and returns the corresponding MSI domain.
+ * Parse the msi-parent property and returns the corresponding MSI domain.
  *
  * Returns: the MSI domain for this device (or NULL on failure).
  */

@@ -718,33 +717,19 @@ struct irq_domain *of_msi_get_domain(struct device *dev,
                                     struct device_node *np,
                                     enum irq_domain_bus_token token)
 {
-       struct device_node *msi_np;
+       struct of_phandle_args args;
        struct irq_domain *d;
+       int index = 0;
 
-       /* Check for a single msi-parent property */
-       msi_np = of_parse_phandle(np, "msi-parent", 0);
-       if (msi_np && !of_property_read_bool(msi_np, "#msi-cells")) {
-               d = irq_find_matching_host(msi_np, token);
-               if (!d)
-                       of_node_put(msi_np);
-               return d;
-       }
-
-       if (token == DOMAIN_BUS_PLATFORM_MSI) {
-               /* Check for the complex msi-parent version */
-               struct of_phandle_args args;
-               int index = 0;

drivers/of/irq.c struct irq_domain *of_msi_get_domain(struct device *dev, · line 726

Quoted 3 lines

drivers/of/irq.c +3 -0

+       while (!of_parse_phandle_with_optional_args(np, "msi-parent",
+                                                   "#msi-cells",
+                                                   index, &args)) {

I guess you just maintained essentially what was here, but of_for_each_phandle() should work here. It's a bit more efficient too because of_parse_phandle_with_optional_args() is implemented using of_for_each_phandle().