From a615c97a22d871984cd99c8659493c9bc5ceb8d9 Mon Sep 17 00:00:00 2001
From: Derek Hower <dhower@qti.qualcomm.com>
Date: Tue, 11 Nov 2025 11:53:49 -0800
Subject: [PATCH] feat: support CSR[name].reset_value() in IDL

---
 backends/cpp_hart_gen/lib/gen_cpp.rb         |  4 ++++
 backends/cpp_hart_gen/templates/csrs.hxx.erb | 11 +++++++++++
 spec/std/isa/csr/sstatus.yaml                |  2 +-
 tools/ruby-gems/idlc/lib/idlc/ast.rb         | 12 +++++++++++-
 4 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/backends/cpp_hart_gen/lib/gen_cpp.rb b/backends/cpp_hart_gen/lib/gen_cpp.rb
index 9fb62c6b73..16bc493ca2 100644
--- a/backends/cpp_hart_gen/lib/gen_cpp.rb
+++ b/backends/cpp_hart_gen/lib/gen_cpp.rb
@@ -270,6 +270,8 @@ def gen_cpp(symtab, indent = 2, indent_spaces: 2)
       if csr_obj.nil?
         if function_name == "sw_read"
           "#{' ' * indent}__UDB_CSR_BY_ADDR(#{csr.idx_expr.gen_cpp(symtab, 0, indent_spaces:)}).#{function_name}(__UDB_XLEN)"
+        elsif function_name == "reset_value"
+          "#{' ' * indent}__UDB_CSR_BY_ADDR(#{csr.idx_expr.gen_cpp(symtab, 0, indent_spaces:)})._#{function_name}()"
         else
           "#{' ' * indent}__UDB_CSR_BY_ADDR(#{csr.idx_expr.gen_cpp(symtab, 0, indent_spaces:)}).#{function_name.gsub('?', '_Q_')}(#{args_cpp.join(', ')})"
         end
@@ -280,6 +282,8 @@ def gen_cpp(symtab, indent = 2, indent_spaces: 2)
           else
             "#{' ' * indent}__UDB_CSR_BY_NAME(#{csr_obj.name})._#{function_name}()"
           end
+        elsif function_name == "reset_value"
+          "#{' ' * indent}__UDB_CSR_BY_NAME(#{csr_obj.name})._#{function_name}()"
         else
           "#{' ' * indent}__UDB_CSR_BY_NAME(#{csr_obj.name}).#{function_name.gsub('?', '_Q_')}(#{args_cpp.join(', ')})"
         end
diff --git a/backends/cpp_hart_gen/templates/csrs.hxx.erb b/backends/cpp_hart_gen/templates/csrs.hxx.erb
index a4ba44afae..0fb5ec20f5 100644
--- a/backends/cpp_hart_gen/templates/csrs.hxx.erb
+++ b/backends/cpp_hart_gen/templates/csrs.hxx.erb
@@ -213,6 +213,17 @@ namespace udb {
     const std::string name() const override { return "<%= csr.name %>"; }
     PrivilegeMode mode() const override { return PrivilegeMode::<%= csr.priv_mode %>; }
     bool writable() const override { return <%= csr.writable %>; }
+    ValueType _reset_value() const {
+      if (defined()) {
+        return 0_b
+        <%- fields_for_xlen.each do |field| -%>
+        | (m_<%= field.name %>.reset_value() << _Bits<64, false>(m_<%= field.name %>.location().lsb))
+        <%- end -%>
+        ;
+      } else {
+        "x"_xb;
+      }
+    }
 
     bool defined() override {
       return <%= csr.defined_by_condition.to_cxx { |ext_name, ext_req|
diff --git a/spec/std/isa/csr/sstatus.yaml b/spec/std/isa/csr/sstatus.yaml
index f634c71795..e22a88cf85 100644
--- a/spec/std/isa/csr/sstatus.yaml
+++ b/spec/std/isa/csr/sstatus.yaml
@@ -28,7 +28,7 @@ fields:
       Alias of `mstatus.SD`.
 
     type: RO-H
-    reset_value: UNDEFINED_LEGAL
+    reset_value(): return CSR[mstatus].reset_value();
     affectedBy: [F, D, V]
   UXL:
     location: 33-32
diff --git a/tools/ruby-gems/idlc/lib/idlc/ast.rb b/tools/ruby-gems/idlc/lib/idlc/ast.rb
index ea179764b1..5af63d647f 100644
--- a/tools/ruby-gems/idlc/lib/idlc/ast.rb
+++ b/tools/ruby-gems/idlc/lib/idlc/ast.rb
@@ -7450,6 +7450,8 @@ def type_check(symtab)
       elsif ["implemented_without?"].include?(function_name)
         type_error "Expecting one argument" unless args.size == 1
         type_error "Expecting an ExtensionName" unless args[0].type(symtab).kind == :enum_ref && args[0].class_name == "ExtensionName"
+      elsif function_name == "reset_value"
+        type_error "unexpected argument(s)" unless args.empty?
       else
         type_error "'#{function_name}' is not a supported CSR function call"
       end
@@ -7458,7 +7460,7 @@ def type_check(symtab)
     def type(symtab)
 
       case function_name
-      when "sw_read"
+      when "sw_read", "reset_value"
         if csr_known?(symtab)
           l = symtab.csr(csr.csr_name).length
           Type.new(:bits, width: (l.nil? ? :unknown : l))
@@ -7506,6 +7508,14 @@ def value(symtab)
         ext_name = extension_name_enum_type.element_names[idx]
 
         cd.implemented_without?(ext_name)
+      when "reset_value"
+        value_error "CSR not knowable" unless csr_known?(symtab)
+        cd = csr_def(symtab)
+        v = cd.reset_value
+        if v == "UNDEFINED_LEGAL"
+          value_error "undefined reset value"
+        end
+        v
       else
         internal_error "TODO: #{function_name}"
       end