On 15.12.20 13:55, Marc Kleine-Budde wrote:
From: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
This patch adds the function can_skb_get_dll_len() which returns the length of
a CAN frame on the data link layer, including Start-of-frame, Identifier,
various other bits, the CRC, the End-of-frame, the Inter frame spacing and the
actual data.
Co-developed-by: Arunachalam Santhanam <arunachalam.santhanam@xxxxxxxxxxxx>
Not-Signed-off-by: Arunachalam Santhanam <arunachalam.santhanam@xxxxxxxxxxxx>
Co-developed-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
Not-Signed-off-by: Vincent Mailhol <mailhol.vincent@xxxxxxxxxx>
Co-developed-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
Signed-off-by: Marc Kleine-Budde <mkl@xxxxxxxxxxxxxx>
---
drivers/net/can/dev.c | 166 ++++++++++++++++++++++++++++++++++++++++
include/linux/can/dev.h | 3 +
2 files changed, 169 insertions(+)
diff --git a/drivers/net/can/dev.c b/drivers/net/can/dev.c
index fa81e3067b3b..e11e3d95453b 100644
--- a/drivers/net/can/dev.c
+++ b/drivers/net/can/dev.c
@@ -81,6 +81,172 @@ u8 can_len2dll_len(u8 len)
}
EXPORT_SYMBOL_GPL(can_len2dll_len);
+/* Size of a Classical CAN Standard Frame
+ *
+ * Name of Field Bits
+ * ---------------------------------------------------------
+ * Start-of-frame 1
+ * Identifier 11
+ * Remote transmission request (RTR) 1
+ * Identifier extension bit (IDE) 1
+ * Reserved bit (r0) 1
+ * Data length code (DLC) 4
+ * Data field 0...64
+ * CRC 15
+ * CRC delimiter 1
+ * ACK slot 1
+ * ACK delimiter 1
+ * End-of-frame (EOF) 7
+ * Inter frame spacing 3
+ *
+ * rounded up and ignoring bitsuffing
bitsTuffing :-)
and in all the other copy/paste locations too
+ */
+#define CAN_DLL_OVERHEAD_SFF DIV_ROUND_UP(47, 8)
+
+/* Size of a Classical CAN Extended Frame
+ *
+ * Name of Field Bits
+ * ---------------------------------------------------------
+ * Start-of-frame 1
+ * Identifier A 11
+ * Substitute remote request (SRR) 1
+ * Identifier extension bit (IDE) 1
+ * Identifier B 18
+ * Remote transmission request (RTR) 1
+ * Reserved bits (r1, r0) 2
+ * Data length code (DLC) 4
+ * Data field 0...64
+ * CRC 15
+ * CRC delimiter 1
+ * ACK slot 1
+ * ACK delimiter 1
+ * End-of-frame (EOF) 7
+ * Inter frame spacing 3
+ *
+ * rounded up and ignoring bitsuffing
+ */
+#define CAN_DLL_OVERHEAD_EFF DIV_ROUND_UP(67, 8)
+
+/* Size of a CAN-FD Standard Frame
+ *
+ * Name of Field Bits
+ * ---------------------------------------------------------
+ * Start-of-frame 1
+ * Identifier 11
+ * Reserved bit (r1) 1
+ * Identifier extension bit (IDE) 1
+ * Flexible data rate format (FDF) 1
+ * Reserved bit (r0) 1
+ * Bit Rate Switch (BRS) 1
+ * Error Status Indicator (ESI) 1
+ * Data length code (DLC) 4
+ * Data field 0...512
+ * Stuff Bit Count (SBC) 4/5 0...16/20...64
+ * CRC 17/21 0...16/20...64
+ * CRC delimiter (CD) 1
+ * ACK slot (AS) 1
+ * ACK delimiter (AD) 1
+ * End-of-frame (EOF) 7
+ * Inter frame spacing 3
+ *
+ * assuming CRC21, rounded up and ignoring bitsuffing
+ */
+#define CANFD_DLL_OVERHEAD_SFF DIV_ROUND_UP(61, 8)
+
+/* Size of a CAN-FD Extended Frame
+ *
+ * Name of Field Bits
+ * ---------------------------------------------------------
+ * Start-of-frame 1
+ * Identifier A 11
+ * Substitute remote request (SRR) 1
+ * Identifier extension bit (IDE) 1
+ * Identifier B 18
+ * Reserved bit (r1) 1
+ * Flexible data rate format (FDF) 1
+ * Reserved bit (r0) 1
+ * Bit Rate Switch (BRS) 1
+ * Error Status Indicator (ESI) 1
+ * Data length code (DLC) 4
+ * Data field 0...512
+ * Stuff Bit Count (SBC) 4/5 0...16/20...64
+ * CRC 17/21 0...16/20...64
+ * CRC delimiter (CD) 1
+ * ACK slot (AS) 1
+ * ACK delimiter (AD) 1
+ * End-of-frame (EOF) 7
+ * Inter frame spacing 3
+ *
+ * assuming CRC21, rounded up and ignoring bitsuffing
+ */
+#define CANFD_DLL_OVERHEAD_EFF DIV_ROUND_UP(80, 8)
+
+/* Maximum size of a Classical CAN frame
+ * (rounded up and ignoring bitsuffing)
+ */
+#define CAN_DLL_LEN_MAX (CAN_DLL_OVERHEAD_EFF + CAN_MAX_DLEN)
+
+/* Maximum size of a CAN-FD frame (rough estimation because
+ * ES58X_SFF_BYTES() and ES58X_EFF_BYTES() macros are using the
+ * constant values for Classical CAN, not CAN-FD).
+ */
+#define CANFD_DLL_LEN_MAX (CANFD_DLL_OVERHEAD_EFF + CANFD_MAX_DLEN)
+
Would it make sense to move these definitions and/or the below code into
a separate can_dll.h file?
we have separated the code to calculate these kind of things in
canframelen.[ch] in the can-utils too.
Regards,
Oliver
+/**
+ * can_skb_get_dll_len() - Calculate the CAN Data Link Layer length in
+ * bytes of a given skb.
+ * @skb: socket buffer of a CAN message.
+ *
+ * Do a rough calculation: bit stuffing is ignored and length in bits
+ * is rounded up to a length in bytes.
+ *
+ * Rationale: this function is to be used for the BQL functions
+ * (netdev_sent_queue() and netdev_completed_queue()) which expect a
+ * value in bytes. Just using skb->len is insufficient because it will
+ * return the constant value of CAN(FD)_MTU. Doing the bit stuffing
+ * calculation would be too expensive in term of computing resources
+ * for no noticeable gain.
+ *
+ * Remarks:
+ * a.) The payload of CAN FD frames with BRS flag are sent at a
+ * different bitrate. Currently, the can-utils canbusload tool does
+ * not support CAN-FD yet and so we could not run any benchmark to
+ * measure the impact. There might be possible improvement here.
+ * b.) The macro CAN_DLL_OVERHEAD_EFF and CAN_DLL_OVERHEAD_SFF are
+ * for classical CAN. Need to do the addition for CAN-FD (the value
+ * are expected to be close enough so the impact should be minimal or
+ * none).
+ *
+ * Return: length in bytes.
+ */
+unsigned int can_skb_get_dll_len(const struct sk_buff *skb)
+{
+ const struct canfd_frame *cf = (const struct canfd_frame *)skb->data;
+ u8 len;
+
+ if (can_is_canfd_skb(skb))
+ len = can_len2dll_len(cf->len);
+ else if (cf->can_id & CAN_RTR_FLAG)
+ len = 0;
+ else
+ len = cf->len;
+
+ if (can_is_canfd_skb(skb)) {
+ if (cf->can_id & CAN_EFF_FLAG)
+ len += CANFD_DLL_OVERHEAD_EFF;
+ else
+ len += CANFD_DLL_OVERHEAD_SFF;
+ } else {
+ if (cf->can_id & CAN_EFF_FLAG)
+ len += CAN_DLL_OVERHEAD_EFF;
+ else
+ len += CAN_DLL_OVERHEAD_SFF;
+ }
+
+ return len;
+}
+EXPORT_SYMBOL_GPL(can_skb_get_dll_len);
+
#ifdef CONFIG_CAN_CALC_BITTIMING
#define CAN_CALC_MAX_ERROR 50 /* in one-tenth of a percent */
diff --git a/include/linux/can/dev.h b/include/linux/can/dev.h
index 27c359a00203..affdee8f64c4 100644
--- a/include/linux/can/dev.h
+++ b/include/linux/can/dev.h
@@ -195,6 +195,9 @@ u8 can_len2dlc(u8 len);
/* map the sanitized data length to an appropriate data link layer length */
u8 can_len2dll_len(u8 len);
+/* get data link layer length of CAN/CAN-FD frame */
+unsigned int can_skb_get_dll_len(const struct sk_buff *skb);
+
struct net_device *alloc_candev_mqs(int sizeof_priv, unsigned int echo_skb_max,
unsigned int txqs, unsigned int rxqs);
#define alloc_candev(sizeof_priv, echo_skb_max) \
