acpid: implement real _CST/_PSS/_PSD/_CPC processor data readers

Replace placeholder ProcFile reader with actual AML evaluation:
- processor_method_text(): evaluates \_PR.CPU{n}.<method> via AML
  interpreter, returns formatted text for each ACPI method type
- format_pss_text(): P-state table (freq/power/latency/control/status)
- format_cst_text(): C-state table (type/latency/power)
- format_psd_text(): P-state dependency domains
- format_cpc_text(): Continuous Performance Control descriptor dump

scheme.rs changes:
- open(): parse CPU{n} path format (processor/CPU0/pss)
- read(): call processor_method_text() instead of placeholder string
- readdir(): return short CPU segment names (CPU0) not full AML paths

drivers/acpid/src/acpi.rs

@@ -1094,6 +1094,263 @@ impl AcpiContext {
             Err(e) => Err(AmlEvalError::from(e)),
         }
     }
+
+    /// Evaluate a no-argument AML processor method (`_PSS`, `_CST`, `_PSD`,
+    /// `_CPC`) and return the result formatted as text for the
+    /// `/scheme/acpi/processor/CPU{n}/<method>` interface.
+    ///
+    /// `cpu_segment` is the processor name segment (e.g. `"CPU0"`). The
+    /// AML path `\_PR.CPU0._PSS` is constructed internally.
+    /// `method` is the ACPI method name (`"_PSS"`, `"_CST"`, `"_PSD"`,
+    /// `"_CPC"`).
+    ///
+    /// Returns the text content. If the method is absent the result is
+    /// `"# not available\n"` for all methods, or `"# not supported\n"`
+    /// for `_CPC` (signalling that the firmware does not advertise
+    /// Collaborative Processor Performance Control).
+    pub fn processor_method_text(&self, cpu_segment: &str, method: &str) -> String {
+        let path = format!("\\_PR.{}.{}", cpu_segment, method);
+        match self.eval_processor_method(&path) {
+            Ok(Some(obj)) => format_processor_result(method, &obj),
+            Ok(None) => {
+                if method == "_CPC" {
+                    "# not supported\n".to_string()
+                } else {
+                    "# not available\n".to_string()
+                }
+            }
+            Err(e) => {
+                log::debug!("acpid: {} evaluation failed: {:?}", path, e);
+                "# not available\n".to_string()
+            }
+        }
+    }
+
+    /// Internal helper: evaluate a no-argument AML method/object and return
+    /// the resulting [`Object`]. Uses [`Interpreter::evaluate_if_present`] so
+    /// that missing objects return `Ok(None)` cleanly rather than an error.
+    fn eval_processor_method(&self, path: &str) -> Result<Option<Object>, AmlEvalError> {
+        let mut symbols = self.aml_symbols.write();
+        let aml_name = AmlName::from_str(path)
+            .map_err(|_| AmlEvalError::DeserializationError)?;
+        let interpreter = symbols.aml_context_mut(None)?;
+        interpreter.acquire_global_lock(16)?;
+
+        let result = interpreter.evaluate_if_present(aml_name, Vec::new());
+        interpreter
+            .release_global_lock()
+            .expect("acpid: failed to release AML global lock");
+
+        match result {
+            Ok(Some(obj)) => {
+                let unwrapped = obj.unwrap_reference();
+                Ok(Some(unwrapped.deref().clone()))
+            }
+            Ok(None) => Ok(None),
+            Err(e) => Err(AmlEvalError::from(e)),
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Processor method text formatting
+// ---------------------------------------------------------------------------
+
+/// Extract a `u64` integer from an AML [`Object`], following references.
+fn obj_as_integer(obj: &Object) -> Option<u64> {
+    match obj {
+        Object::Integer(n) => Some(*n),
+        Object::Reference { inner, .. } => obj_as_integer(inner.deref()),
+        _ => None,
+    }
+}
+
+/// Extract the inner elements of an AML `Package` [`Object`], following
+/// references. Returns `None` for non-package objects.
+fn obj_as_package(obj: &Object) -> Option<&[WrappedObject]> {
+    match obj {
+        Object::Package(elements) => Some(elements.as_slice()),
+        Object::Reference { inner, .. } => obj_as_package(inner.deref()),
+        _ => None,
+    }
+}
+
+/// Convenience: extract an integer from a [`WrappedObject`] package element.
+fn elem_as_integer(wo: &WrappedObject) -> Option<u64> {
+    obj_as_integer(wo.deref())
+}
+
+/// Convenience: extract a sub-package slice from a [`WrappedObject`] element.
+fn elem_as_package(wo: &WrappedObject) -> Option<&[WrappedObject]> {
+    obj_as_package(wo.deref())
+}
+
+/// Dispatch formatting based on the ACPI method name.
+fn format_processor_result(method: &str, obj: &Object) -> String {
+    let elements = match obj_as_package(obj) {
+        Some(e) => e,
+        None => {
+            log::debug!("acpid: {} returned non-package object: {}", method, obj);
+            return "# not available\n".to_string();
+        }
+    };
+    match method {
+        "_PSS" => format_pss_text(elements),
+        "_CST" => format_cst_text(elements),
+        "_PSD" => format_psd_text(elements),
+        "_CPC" => format_cpc_text(elements),
+        _ => "# not available\n".to_string(),
+    }
+}
+
+/// Format `_PSS` (Performance Supported States) as text.
+///
+/// `_PSS` returns a Package of sub-packages. Each sub-package contains six
+/// integers: `[CoreFrequency(MHz), Power(mW), TransitionLatency(µs),
+/// BusMasterLatency(µs), Control, Status]`.
+///
+/// Output — one header line, then one data line per P-state:
+/// ```text
+/// # _PSS: core_freq_mhz power_mw trans_latency_us bus_latency_us control status
+/// 3400 35 10 50 0x00001A00 0x00001A00
+/// ```
+fn format_pss_text(elements: &[WrappedObject]) -> String {
+    let mut out = String::from(
+        "# _PSS: core_freq_mhz power_mw trans_latency_us bus_latency_us control status\n",
+    );
+    let mut count = 0;
+    for element in elements {
+        if let Some(sub) = elem_as_package(element) {
+            let vals: Vec<u64> = sub.iter().filter_map(elem_as_integer).collect();
+            if vals.len() >= 6 {
+                out.push_str(&format!(
+                    "{} {} {} {} 0x{:08X} 0x{:08X}\n",
+                    vals[0], vals[1], vals[2], vals[3], vals[4], vals[5]
+                ));
+                count += 1;
+            } else {
+                log::debug!("_PSS sub-package has {} integers, expected >= 6", vals.len());
+            }
+        }
+    }
+    if count == 0 {
+        out.push_str("# no P-states\n");
+    }
+    out
+}
+
+/// Format `_CST` (C-State Table) as text.
+///
+/// `_CST` returns a Package whose first element is a count integer,
+/// followed by that many C-state descriptor sub-packages. Each
+/// sub-package contains `[CStateType, Latency(µs), Power(mW),
+/// Register(Buffer), Register(Buffer)]`.
+///
+/// Output — one header line, then one data line per C-state:
+/// ```text
+/// # _CST: type latency_us power_mw
+/// 1 1 1000
+/// 2 80 500
+/// 3 1000 10
+/// ```
+fn format_cst_text(elements: &[WrappedObject]) -> String {
+    let mut out = String::from("# _CST: type latency_us power_mw\n");
+    // Element[0] is the C-state count (an Integer). If the first element
+    // is an integer we skip it; otherwise we start from index 0 to
+    // tolerate non-standard firmware.
+    let start = if elements.first().map(elem_as_integer).is_some() {
+        1
+    } else {
+        0
+    };
+    let mut count = 0;
+    for element in elements.iter().skip(start) {
+        if let Some(sub) = elem_as_package(element) {
+            let vals: Vec<u64> = sub.iter().filter_map(elem_as_integer).collect();
+            if vals.len() >= 3 {
+                out.push_str(&format!("{} {} {}\n", vals[0], vals[1], vals[2]));
+                count += 1;
+            }
+        }
+    }
+    if count == 0 {
+        out.push_str("# no C-states\n");
+    }
+    out
+}
+
+/// Format `_PSD` (P-State Dependency) as text.
+///
+/// `_PSD` returns a Package of dependency sub-packages. Each sub-package
+/// contains five integers: `[NumEntries, Revision, Domain, CoordType,
+/// NumProcessors]`.
+///
+/// Output — one header line, then one data line per domain:
+/// ```text
+/// # _PSD: num_entries revision domain coord_type num_processors
+/// 5 0 0 0xFC 8
+/// ```
+fn format_psd_text(elements: &[WrappedObject]) -> String {
+    let mut out = String::from(
+        "# _PSD: num_entries revision domain coord_type num_processors\n",
+    );
+    let mut count = 0;
+    for element in elements {
+        if let Some(sub) = elem_as_package(element) {
+            let vals: Vec<u64> = sub.iter().filter_map(elem_as_integer).collect();
+            if vals.len() >= 5 {
+                out.push_str(&format!(
+                    "{} {} {} 0x{:02X} {}\n",
+                    vals[0], vals[1], vals[2], vals[3], vals[4]
+                ));
+                count += 1;
+            }
+        }
+    }
+    if count == 0 {
+        out.push_str("# no P-state dependencies\n");
+    }
+    out
+}
+
+/// Format `_CPC` (Continuous Performance Control) as text.
+///
+/// `_CPC` returns a Package of mixed Integer and Buffer (Generic Address
+/// Structure) descriptors defined in ACPI 6.5 §8.4.7.1. The layout is
+/// vendor-specific in practice, so this is a best-effort index dump:
+/// integers are printed by index, buffers are noted as register
+/// descriptors.
+fn format_cpc_text(elements: &[WrappedObject]) -> String {
+    let mut out = String::from("# _CPC: continuous performance control\n");
+    let mut found = false;
+    for (idx, element) in elements.iter().enumerate() {
+        match element.deref() {
+            Object::Integer(n) => {
+                out.push_str(&format!("cpc[{}]: {}\n", idx, n));
+                found = true;
+            }
+            Object::Buffer(_) => {
+                out.push_str(&format!("cpc[{}]: <register>\n", idx));
+                found = true;
+            }
+            Object::Reference { inner, .. } => match inner.deref() {
+                Object::Integer(n) => {
+                    out.push_str(&format!("cpc[{}]: {}\n", idx, n));
+                    found = true;
+                }
+                Object::Buffer(_) => {
+                    out.push_str(&format!("cpc[{}]: <register>\n", idx));
+                    found = true;
+                }
+                _ => {}
+            },
+            _ => {}
+        }
+    }
+    if !found {
+        out.push_str("# empty\n");
+    }
+    out
 }
 
 #[repr(C, packed)]

drivers/acpid/src/scheme.rs

@@ -394,7 +394,10 @@ impl SchemeSync for AcpiScheme<'_, '_> {
 
                     ["processor", cpu_str, file] => {
                         // /scheme/acpi/processor/<cpu>/{pss,psd,cst,cpc}
-                        let cpu: u32 = cpu_str.parse().map_err(|_| Error::new(EINVAL))?;
+                        let cpu: u32 = cpu_str
+                            .strip_prefix("CPU")
+                            .and_then(|rest| rest.parse().ok())
+                            .ok_or(Error::new(EINVAL))?;
                         let kind = match *file {
                             "pss" => ProcFileKind::Pss,
                             "psd" => ProcFileKind::Psd,
@@ -512,13 +515,18 @@ impl SchemeSync for AcpiScheme<'_, '_> {
             HandleKind::Processor | HandleKind::DmiDir | HandleKind::Thermal | HandleKind::Power | HandleKind::Symbols(_) | HandleKind::RegisterPci | HandleKind::TopLevel | HandleKind::SchemeRoot => {
                 return Err(Error::new(EISDIR));
             }
-            HandleKind::ProcFile { .. } => {
+            HandleKind::ProcFile { cpu, kind } => {
-                // Per-CPU _PSS / _PSD / _CST / _CPC text export. The
+                let method = match kind {
-                // full AML→text conversion is a Phase G follow-up; for
+                    ProcFileKind::Pss => "_PSS",
-                // now, return a placeholder line so consumers
+                    ProcFileKind::Psd => "_PSD",
-                // (cpufreqd, redbear-power) can detect the path is
+                    ProcFileKind::Cst => "_CST",
-                // present and report "no data" without getting ENOENT.
+                    ProcFileKind::Cpc => "_CPC",
-                proc_buf = b"# ACPI processor data not yet populated\n".to_vec();
+                };
+                let cpu_segment = format!("CPU{}", cpu);
+                proc_buf = self
+                    .ctx
+                    .processor_method_text(&cpu_segment, method)
+                    .into_bytes();
                 proc_buf.as_slice()
             }
             HandleKind::Tables => return Err(Error::new(EISDIR)),
@@ -624,13 +632,16 @@ impl SchemeSync for AcpiScheme<'_, '_> {
                 // Enumerate \_PR.<cpu> entries from the AML namespace.
                 // Returns Ok with no entries on systems with no
                 // processors (headless QEMU with no DSDT) so consumers
-                // see an empty-but-existing directory.
+                // see an empty-but-existing directory. The directory
+                // entry names use the short CPU segment (e.g. "CPU0")
+                // so that `processor/CPU0/pss` is a valid sub-path.
                 let cpus = self.ctx.cpu_names();
-                for (idx, cpu_name) in cpus.iter().enumerate().skip(opaque_offset as usize) {
+                for (idx, cpu_path) in cpus.iter().enumerate().skip(opaque_offset as usize) {
+                    let short = cpu_path.strip_prefix("\\_PR.").unwrap_or(cpu_path);
                     buf.entry(DirEntry {
                         inode: 0,
                         next_opaque_id: idx as u64 + 1,
-                        name: cpu_name.as_str(),
+                        name: short,
                         kind: DirentKind::Directory,
                     })?;
                 }