iwlwifi: document shared Tx structures

Document shared Tx structures
Signed-off-by: NBen Cahill <ben.m.cahill@intel.com>
Signed-off-by: NZhu Yi <yi.zhu@intel.com>
Signed-off-by: NJohn W. Linville <linville@tuxdriver.com>

drivers/net/wireless/iwlwifi/iwl-4965-hw.h

@@ -452,6 +452,13 @@ struct iwl4965_eeprom {
  */
 #define CSR_HW_REV_WA_REG	(CSR_BASE+0x22C)
 
+/* Hardware interface configuration bits */
+#define CSR_HW_IF_CONFIG_REG_BIT_KEDRON_R	(0x00000010)
+#define CSR_HW_IF_CONFIG_REG_MSK_BOARD_VER	(0x00000C00)
+#define CSR_HW_IF_CONFIG_REG_BIT_MAC_SI		(0x00000100)
+#define CSR_HW_IF_CONFIG_REG_BIT_RADIO_SI	(0x00000200)
+#define CSR_HW_IF_CONFIG_REG_BIT_EEPROM_OWN_SEM (0x00200000)
+
 /* interrupt flags in INTA, set by uCode or hardware (e.g. dma),
  * acknowledged (reset) by host writing "1" to flagged bits. */
 #define CSR_INT_BIT_FH_RX        (1<<31) /* Rx DMA, cmd responses, FH_INT[17:16] */
@@ -1574,12 +1581,6 @@ enum {
 #define SCD_QUEUE_CTX_REG2_FRAME_LIMIT_POS	(16)
 #define SCD_QUEUE_CTX_REG2_FRAME_LIMIT_MSK	(0x007F0000)
 
-#define CSR_HW_IF_CONFIG_REG_BIT_KEDRON_R	(0x00000010)
-#define CSR_HW_IF_CONFIG_REG_MSK_BOARD_VER	(0x00000C00)
-#define CSR_HW_IF_CONFIG_REG_BIT_MAC_SI		(0x00000100)
-#define CSR_HW_IF_CONFIG_REG_BIT_RADIO_SI	(0x00000200)
-#define CSR_HW_IF_CONFIG_REG_BIT_EEPROM_OWN_SEM (0x00200000)
-
 static inline u8 iwl4965_hw_get_rate(__le32 rate_n_flags)
 {
 	return le32_to_cpu(rate_n_flags) & 0xFF;
@@ -1593,6 +1594,53 @@ static inline __le32 iwl4965_hw_set_rate_n_flags(u8 rate, u16 flags)
 	return cpu_to_le32(flags|(u16)rate);
 }
 
+
+/**
+ * Tx/Rx Queues
+ *
+ * Most communication between driver and 4965 is via queues of data buffers.
+ * For example, all commands that the driver issues to device's embedded
+ * controller (uCode) are via the command queue (one of the Tx queues).  All
+ * uCode command responses/replies/notifications, including Rx frames, are
+ * conveyed from uCode to driver via the Rx queue.
+ *
+ * Most support for these queues, including handshake support, resides in
+ * structures in host DRAM, shared between the driver and the device.  When
+ * allocating this memory, the driver must make sure that data written by
+ * the host CPU updates DRAM immediately (and does not get "stuck" in CPU's
+ * cache memory), so DRAM and cache are consistent, and the device can
+ * immediately see changes made by the driver.
+ *
+ * 4965 supports up to 16 DRAM-based Tx queues, and services these queues via
+ * up to 7 DMA channels (FIFOs).  Each Tx queue is supported by a circular array
+ * in DRAM containing 256 Transmit Frame Descriptors (TFDs).
+ */
+#define IWL4965_MAX_WIN_SIZE              64
+#define IWL4965_QUEUE_SIZE               256
+#define IWL4965_NUM_FIFOS                  7
+#define IWL_MAX_NUM_QUEUES                16
+
+
+/**
+ * struct iwl4965_tfd_frame_data
+ *
+ * Describes up to 2 buffers containing (contiguous) portions of a Tx frame.
+ * Each buffer must be on dword boundary.
+ * Up to 10 iwl_tfd_frame_data structures, describing up to 20 buffers,
+ * may be filled within a TFD (iwl_tfd_frame).
+ *
+ * Bit fields in tb1_addr:
+ * 31- 0: Tx buffer 1 address bits [31:0]
+ *
+ * Bit fields in val1:
+ * 31-16: Tx buffer 2 address bits [15:0]
+ * 15- 4: Tx buffer 1 length (bytes)
+ *  3- 0: Tx buffer 1 address bits [32:32]
+ *
+ * Bit fields in val2:
+ * 31-20: Tx buffer 2 length (bytes)
+ * 19- 0: Tx buffer 2 address bits [35:16]
+ */
 struct iwl4965_tfd_frame_data {
 	__le32 tb1_addr;
 
@@ -1621,6 +1669,35 @@ struct iwl4965_tfd_frame_data {
 #define IWL_tb2_len_SYM val2
 } __attribute__ ((packed));
 
+
+/**
+ * struct iwl4965_tfd_frame
+ *
+ * Transmit Frame Descriptor (TFD)
+ *
+ * 4965 supports up to 16 Tx queues resident in host DRAM.
+ * Each Tx queue uses a circular buffer of 256 TFDs stored in host DRAM.
+ * Both driver and device share these circular buffers, each of which must be
+ * contiguous 256 TFDs x 128 bytes-per-TFD = 32 KBytes for 4965.
+ *
+ * Driver must indicate the physical address of the base of each
+ * circular buffer via the 4965's FH_MEM_CBBC_QUEUE registers.
+ *
+ * Each TFD contains pointer/size information for up to 20 data buffers
+ * in host DRAM.  These buffers collectively contain the (one) frame described
+ * by the TFD.  Each buffer must be a single contiguous block of memory within
+ * itself, but buffers may be scattered in host DRAM.  Each buffer has max size
+ * of (4K - 4).  The 4965 concatenates all of a TFD's buffers into a single
+ * Tx frame, up to 8 KBytes in size.
+ *
+ * Bit fields in the control dword (val0):
+ * 31-30: # dwords (0-3) of padding required at end of frame for 16-byte bound
+ *    29: reserved
+ * 28-24: # Transmit Buffer Descriptors in TFD
+ * 23- 0: reserved
+ *
+ * A maximum of 255 (not 256!) TFDs may be on a queue waiting for Tx.
+ */
 struct iwl4965_tfd_frame {
 	__le32 val0;
 	/* __le32 rsvd1:24; */
@@ -1634,11 +1711,16 @@ struct iwl4965_tfd_frame {
 	__le32 reserved;
 } __attribute__ ((packed));
 
-#define IWL4965_MAX_WIN_SIZE              64
-#define IWL4965_QUEUE_SIZE               256
-#define IWL4965_NUM_FIFOS                  7
-#define IWL_MAX_NUM_QUEUES                16
 
+/**
+ * struct iwl4965_queue_byte_cnt_entry
+ *
+ * Byte Count Table Entry
+ *
+ * Bit fields:
+ * 15-12: reserved
+ * 11- 0: total to-be-transmitted byte count of frame (does not include command)
+ */
 struct iwl4965_queue_byte_cnt_entry {
 	__le16 val;
 	/* __le16 byte_cnt:12; */
@@ -1648,6 +1730,25 @@ struct iwl4965_queue_byte_cnt_entry {
 	/* __le16 rsvd:4; */
 } __attribute__ ((packed));
 
+
+/**
+ * struct iwl4965_sched_queue_byte_cnt_tbl
+ *
+ * Byte Count table
+ *
+ * Each Tx queue uses a byte-count table containing 320 entries:
+ * one 16-bit entry for each of 256 TFDs, plus an additional 64 entries that
+ * duplicate the first 64 entries (to avoid wrap-around within a Tx window;
+ * max Tx window is 64 TFDs).
+ *
+ * When driver sets up a new TFD, it must also enter the total byte count
+ * of the frame to be transmitted into the corresponding entry in the byte
+ * count table for the chosen Tx queue.  If the TFD index is 0-63, the driver
+ * must duplicate the byte count entry in corresponding index 256-319.
+ *
+ * "dont_care" padding puts each byte count table on a 1024-byte boundary;
+ * 4965 assumes tables are separated by 1024 bytes.
+ */
 struct iwl4965_sched_queue_byte_cnt_tbl {
 	struct iwl4965_queue_byte_cnt_entry tfd_offset[IWL4965_QUEUE_SIZE +
 						       IWL4965_MAX_WIN_SIZE];
@@ -1656,8 +1757,30 @@ struct iwl4965_sched_queue_byte_cnt_tbl {
 		     sizeof(__le16)];
 } __attribute__ ((packed));
 
-/* Base physical address of iwl4965_shared is provided to KDR_SCD_DRAM_BASE_ADDR
- * and &iwl4965_shared.val0 is provided to FH_RSCSR_CHNL0_STTS_WPTR_REG */
+
+/**
+ * struct iwl4965_shared - handshake area for Tx and Rx
+ *
+ * For convenience in allocating memory, this structure combines 2 areas of
+ * DRAM which must be shared between driver and 4965.  These do not need to
+ * be combined, if better allocation would result from keeping them separate:
+ *
+ * 1)  The Tx byte count tables occupy 1024 bytes each (16 KBytes total for
+ *     16 queues).  Driver uses SCD_DRAM_BASE_ADDR to tell 4965 where to find
+ *     the first of these tables.  4965 assumes tables are 1024 bytes apart.
+ *
+ * 2)  The Rx status (val0 and val1) occupies only 8 bytes.  Driver uses
+ *     FH_RSCSR_CHNL0_STTS_WPTR_REG to tell 4965 where to find this area.
+ *     Driver reads val0 to determine the latest Receive Buffer Descriptor (RBD)
+ *     that has been filled by the 4965.
+ *
+ * Bit fields val0:
+ * 31-12:  Not used
+ * 11- 0:  Index of last filled Rx buffer descriptor (4965 writes, driver reads)
+ *
+ * Bit fields val1:
+ * 31- 0:  Not used
+ */
 struct iwl4965_shared {
 	struct iwl4965_sched_queue_byte_cnt_tbl
 	 queues_byte_cnt_tbls[IWL_MAX_NUM_QUEUES];