Re: [RFC PATCH 25/36] arm_mpam: Register and enable IRQs

Hi Fenghua,

On 04/08/2025 17:53, Fenghua Yu wrote:

On 7/11/25 11:36, James Morse wrote:

quoted

Register and enable error IRQs. All the MPAM error interrupts indicate a
software bug, e.g. out of range partid. If the error interrupt is ever
signalled, attempt to disable MPAM.

Only the irq handler accesses the ESR register, so no locking is needed.
The work to disable MPAM after an error needs to happen at process
context, use a threaded interrupt.

There is no support for percpu threaded interrupts, for now schedule
the work to be done from the irq handler.

Enabling the IRQs in the MSC may involve cross calling to a CPU that
can access the MSC.

quoted

+static int mpam_register_irqs(void)
+{
+    int err, irq, idx;
+    struct mpam_msc *msc;
+
+    lockdep_assert_cpus_held();
+
+    idx = srcu_read_lock(&mpam_srcu);
+    list_for_each_entry_srcu(msc, &mpam_all_msc, glbl_list,
srcu_read_lock_held(&mpam_srcu)) {
+        irq = platform_get_irq_byname_optional(msc->pdev, "error");
+        if (irq <= 0)
+            continue;
+
+        /* The MPAM spec says the interrupt can be SPI, PPI or LPI */
+        /* We anticipate sharing the interrupt with other MSCs */
+        if (irq_is_percpu(irq)) {
+            err = request_percpu_irq(irq, &mpam_ppi_handler,
+                         "mpam:msc:error",
+                         msc->error_dev_id);
+            if (err)
+                return err;

But right now mpam_srcu is still being locked. Need to unlock it before return.

Yup, Jonathan's srcu guard runes solve that in a future proof way.


Thanks,

James