sh: intc: userimask support.

This adds support for hardware-assisted userspace irq masking for
special priority levels. Due to the SR.IMASK interactivity, only some
platforms implement this in hardware (including but not limited to
SH-4A interrupt controllers, and ARM-based SH-Mobile CPUs). Each CPU
needs to wire this up on its own, for now only SH7786 is wired up as an
example.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

2 files changed, 80 insertions, 2 deletions

diff --git a/drivers/sh/Kconfig b/drivers/sh/Kconfig
new file mode 100644
index 000000000000..22c3cdaf22fe
--- /dev/null
+++ b/drivers/sh/Kconfig
@@ -0,0 +1,13 @@
+config INTC_USERIMASK
+        bool "Userspace interrupt masking support"
+        depends on ARCH_SHMOBILE || (SUPERH && CPU_SH4A)
+        help
+          This enables support for hardware-assisted userspace hardirq
+          masking.
+
+          SH-4A and newer interrupt blocks all support a special shadowed
+          page with all non-masking registers obscured when mapped in to
+          userspace. This is primarily for use by userspace device
+          drivers that are using special priority levels.
+
+          If in doubt, say N.
diff --git a/drivers/sh/intc.c b/drivers/sh/intc.c
index 65e15828faaa..77d10acf1884 100644
--- a/drivers/sh/intc.c
+++ b/drivers/sh/intc.c
@@ -27,6 +27,7 @@
 #include <linux/topology.h>
 #include <linux/bitmap.h>
 #include <linux/cpumask.h>
+#include <asm/sizes.h>
 
 #define _INTC_MK(fn, mode, addr_e, addr_d, width, shift) \
         ((shift) | ((width) << 5) | ((fn) << 9) | ((mode) << 13) | \
@@ -94,7 +95,8 @@ static DEFINE_SPINLOCK(vector_lock);
 #define SMP_NR(d, x) 1
 #endif
 
-static unsigned int intc_prio_level[NR_IRQS]; /* for now */
+static unsigned int intc_prio_level[NR_IRQS];   /* for now */
+static unsigned int default_prio_level = 2;     /* 2 - 16 */
 static unsigned long ack_handle[NR_IRQS];
 
 static inline struct intc_desc_int *get_intc_desc(unsigned int irq)
@@ -787,7 +789,7 @@ static void __init intc_register_irq(struct intc_desc *desc,
         /* set priority level
          * - this needs to be at least 2 for 5-bit priorities on 7780
          */
-        intc_prio_level[irq] = 2;
+        intc_prio_level[irq] = default_prio_level;
 
         /* enable secondary masking method if present */
         if (data[!primary])
@@ -1037,6 +1039,64 @@ err0:
         return -ENOMEM;
 }
 
+#ifdef CONFIG_INTC_USERIMASK
+static void __iomem *uimask;
+
+int register_intc_userimask(unsigned long addr)
+{
+        if (unlikely(uimask))
+                return -EBUSY;
+
+        uimask = ioremap_nocache(addr, SZ_4K);
+        if (unlikely(!uimask))
+                return -ENOMEM;
+
+        pr_info("intc: userimask support registered for levels 0 -> %d\n",
+                default_prio_level - 1);
+
+        return 0;
+}
+
+static ssize_t
+show_intc_userimask(struct sysdev_class *cls,
+                    struct sysdev_class_attribute *attr, char *buf)
+{
+        return sprintf(buf, "%d\n", (__raw_readl(uimask) >> 4) & 0xf);
+}
+
+static ssize_t
+store_intc_userimask(struct sysdev_class *cls,
+                     struct sysdev_class_attribute *attr,
+                     const char *buf, size_t count)
+{
+        unsigned long level;
+
+        level = simple_strtoul(buf, NULL, 10);
+
+        /*
+         * Minimal acceptable IRQ levels are in the 2 - 16 range, but
+         * these are chomped so as to not interfere with normal IRQs.
+         *
+         * Level 1 is a special case on some CPUs in that it's not
+         * directly settable, but given that USERIMASK cuts off below a
+         * certain level, we don't care about this limitation here.
+         * Level 0 on the other hand equates to user masking disabled.
+         *
+         * We use default_prio_level as a cut off so that only special
+         * case opt-in IRQs can be mangled.
+         */
+        if (level >= default_prio_level)
+                return -EINVAL;
+
+        __raw_writel(0xa5 << 24 | level << 4, uimask);
+
+        return count;
+}
+
+static SYSDEV_CLASS_ATTR(userimask, S_IRUSR | S_IWUSR,
+                         show_intc_userimask, store_intc_userimask);
+#endif
+
 static ssize_t
 show_intc_name(struct sys_device *dev, struct sysdev_attribute *attr, char *buf)
 {
@@ -1108,6 +1168,11 @@ static int __init register_intc_sysdevs(void)
         int id = 0;
 
         error = sysdev_class_register(&intc_sysdev_class);
+#ifdef CONFIG_INTC_USERIMASK
+        if (!error && uimask)
+                error = sysdev_class_create_file(&intc_sysdev_class,
+                                                 &attr_userimask);
+#endif
         if (!error) {
                 list_for_each_entry(d, &intc_list, list) {
                         d->sysdev.id = id;