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Re: [PATCH v6 1/7] xen/riscv: imsic_init() implementation




On 7/8/25 3:52 PM, Jan Beulich wrote:
On 07.07.2025 11:01, Oleksii Kurochko wrote:
imsic_init() is introduced to parse device tree node, which has the following
bindings [2], and based on the parsed information update IMSIC configuration
which is stored in imsic_cfg.

The following helpers are introduces for imsic_init() usage:
  - imsic_parse_node() parses IMSIC node from DTS
  - imsic_get_parent_hartid() returns the hart ( CPU ) ID of the given device
    tree node.

This patch is based on the code from [1].

Since Microchip originally developed imsic.{c,h}, an internal discussion with
them led to the decision to use the MIT license.

[1] https://gitlab.com/xen-project/people/olkur/xen/-/commit/0b1a94f2bc3bb1a81cd26bb75f0bf578f84cb4d4
[2] https://elixir.bootlin.com/linux/v6.12/source/Documentation/devicetree/bindings/interrupt-controller/riscv,imsics.yaml

Co-developed-by: Romain Caritey <Romain.Caritey@xxxxxxxxxxxxx>
Signed-off-by: Oleksii Kurochko <oleksii.kurochko@xxxxxxxxx>
Acked-by: Jan Beulich <jbeulich@xxxxxxxx

I'm curious though:

--- a/xen/arch/riscv/include/asm/smp.h
+++ b/xen/arch/riscv/include/asm/smp.h
@@ -3,6 +3,7 @@
 #define ASM__RISCV__SMP_H
 
 #include <xen/cpumask.h>
+#include <xen/macros.h>
 #include <xen/percpu.h>
 
 #include <asm/current.h>
@@ -18,6 +19,18 @@ static inline unsigned long cpuid_to_hartid(unsigned long cpuid)
     return pcpu_info[cpuid].hart_id;
 }
 
+static inline unsigned int hartid_to_cpuid(unsigned long hartid)
+{
+    for ( unsigned int cpu = 0; cpu < ARRAY_SIZE(pcpu_info); cpu++ )
+    {
+        if ( hartid == cpuid_to_hartid(cpu) )
+            return cpu;
+    }
+
+    /* hartid isn't valid for some reason */
+    return NR_CPUS;
+}
Since there's no FIXME or alike here, is this really intended to remain this
way? With many CPUs this form of lookup can be pretty inefficient.
In the case with a big amount of CPUs it will require to update it. I will create
TODO task in my repo to not forget to update it in a future.

Thanks.

~ Oleksii

 


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