x86_64/device_io: simplify implementation

1 files changed, 53 insertions, 102 deletions

diff --git a/arch/x86_64/include/x86_64/device_io/port_io.hpp b/arch/x86_64/include/x86_64/device_io/port_io.hpp
index 352a4d0..ceabf4a 100644
--- a/arch/x86_64/include/x86_64/device_io/port_io.hpp
+++ b/arch/x86_64/include/x86_64/device_io/port_io.hpp
@@ -1,130 +1,81 @@
 #ifndef TEACHOS_X86_64_IO_PORT_IO_HPP
 #define TEACHOS_X86_64_IO_PORT_IO_HPP
 
+#include <array>
 #include <cstddef>
 #include <cstdint>
+#include <string_view>
 #include <type_traits>
 
 namespace teachos::io::x86_64
 {
-  /**
-   * @brief An I/O port of a given size at a given address.
-   *
-   * @tparam Address The address (port number) of the I/O port.
-   * @tparam Size The size (in bytes) of the I/O port.
-   */
+
+  //! An I/O port of a given size at a given address.
+  //!
+  //! Port I/O leverages a separate address space to communicate with devices via the memory bus, allowing for byte to
+  //! double-word sized transfers.
+  //!
+  //! @tparam Address The address (port number) of the I/O port.
+  //! @tparam Size The size (in bytes) of the I/O port.
   template<std::uint16_t Address, std::size_t Size>
+    requires(Size == 1 || Size == 2 || Size == 4)
   struct port
   {
-    static_assert(Size == 1 || Size == 2 || Size == 4, "A port must be either 1, 2, or 4 bytes in size");
-
-    /**
-     * @brief The type of data available for reading and writing through this port.
-     */
-    using io_type =
+    //! The type of data available for reading and writing through this port.
+    using value_type =
         std::conditional_t<Size == 1, std::byte, std::conditional_t<Size == 2, std::uint16_t, std::uint32_t>>;
 
-    /**
-     * @brief Write a byte to the I/O port.
-     *
-     * @param data The data to write to the I/O port.
-     */
-    auto static write(io_type data) -> void
-      requires(Size == 1)
+    //! Read from the I/O port.
+    //!
+    //! @return The data read from the I/O port.
+    auto static read() noexcept -> value_type
     {
-      asm volatile("mov %[port], %%dx\n"
-                   "mov %[data], %%al\n"
-                   "out %%al, %%dx\n"
-                   :
-                   : [port] "i"(Address), [data] "im"(data)
-                   : "dx", "al");
+      auto data = value_type{};
+      asm volatile((read_code[asm_template_index])
+                   : [data] "=m"(data)
+                   : [port] "i"(Address)
+                   : "dx", (data_register[asm_template_index]));
+      return data;
     }
 
-    /**
-     * @brief Write a word to the I/O port.
-     *
-     * @param data The data to write to the I/O port.
-     */
-    auto static write(io_type data) -> void
-      requires(Size == 2)
+    //! Write data to the I/O port.
+    //!
+    //! @param data The data to write to the I/O port.
+    auto static write(value_type data) noexcept -> void
     {
-      asm volatile("mov %[port], %%dx\n"
-                   "mov %[data], %%ax\n"
-                   "out %%ax, %%dx\n"
+      asm volatile((write_code[asm_template_index])
                    :
                    : [port] "i"(Address), [data] "im"(data)
-                   : "dx", "ax");
+                   : "dx", (data_register[asm_template_index]));
     }
 
-    /**
-     * @brief Write a double-word to the I/O port.
-     *
-     * @param data The data to write to the I/O port.
-     */
-    auto static write(io_type data) -> void
-      requires(Size == 4)
-    {
-      asm volatile("mov %[port], %%dx\n"
-                   "mov %[data], %%eax\n"
-                   "out %%eax, %%dx\n"
-                   :
-                   : [port] "i"(Address), [data] "im"(data)
-                   : "dx", "eax");
-    }
+  private:
+    //! The index into the assembly template and register arrays.
+    //!
+    //! This index is used to select the correct assembly templates for the given operation (read or write), as well as
+    //! the clobbered data register, from the relevant template arrays.
+    constexpr auto static asm_template_index = Size / 2;
 
-    /**
-     * @brief Read a byte from the I/O port.
-     *
-     * @return The data read from the I/O port.
-     */
-    auto static read() -> io_type
-      requires(Size == 1)
-    {
-      auto data = io_type{};
-      asm volatile("mov %[port], %%dx\n"
-                   "in %%dx, %%al\n"
-                   "mov %%al, %[data]\n"
-                   : [data] "=m"(data)
-                   : [port] "i"(Address)
-                   : "dx", "al");
-      return data;
-    }
+    //! The assembly templates used for reading from an I/O port.
+    constexpr auto static read_code = std::array{
+      std::string_view{"mov %[port], %%dx\nin %%dx, %%al\nmov %%al, %[data]"},
+      std::string_view{"mov %[port], %%dx\nin %%dx, %%ax\nmov %%ax, %[data]"},
+      std::string_view{"mov %[port], %%dx\nin %%dx, %%eax\nmov %%eax, %[data]"},
+    };
 
-    /**
-     * @brief Read a word from the I/O port.
-     *
-     * @return The data read from the I/O port.
-     */
-    auto static read() -> io_type
-      requires(Size == 2)
-    {
-      auto data = io_type{};
-      asm volatile("mov %[port], %%dx\n"
-                   "in %%dx, %%ax\n"
-                   "mov %%ax, %[data]\n"
-                   : [data] "=m"(data)
-                   : [port] "i"(Address)
-                   : "dx", "ax");
-      return data;
-    }
+    //! The assembly templates used for writing to an I/O port.
+    constexpr auto static write_code = std::array{
+      std::string_view{"mov %[port], %%dx\nmov %%dx, %[data]\nout %%al, %%dx"},
+      std::string_view{"mov %[port], %%dx\nmov %%dx, %[data]\nout %%ax, %%dx"},
+      std::string_view{"mov %[port], %%dx\nmov %%dx, %[data]\nout %%eax, %%dx"},
+    };
 
-    /**
-     * @brief Read a double-word from the I/O port.
-     *
-     * @return The data read from the I/O port.
-     */
-    auto static read() -> io_type
-      requires(Size == 4)
-    {
-      auto data = io_type{};
-      asm volatile("mov %[port], %%dx\n"
-                   "in %%dx, %%eax\n"
-                   "mov %%eax, %[data]\n"
-                   : [data] "=m"(data)
-                   : [port] "i"(Address)
-                   : "dx", "eax");
-      return data;
-    }
+    //! The registers clobbered by the I/O operation.
+    constexpr auto static data_register = std::array{
+      std::string_view{"al"},
+      std::string_view{"ax"},
+      std::string_view{"eax"},
+    };
   };
 
 }  // namespace teachos::io::x86_64