can: mcp25xxfd: optimize TEF read avoiding unnecessary SPI transfers

We have already enough information to know how many tx-messages have
been terminated so that we do not have to query TEF every time if
there is anything pending but we can read the tefs blindly.

This avoids 1 SPI transfer per TEF read.

Signed-off-by: Martin Sperl <kernel@martin.sperl.org>

drivers/net/can/spi/mcp25xxfd/mcp25xxfd_can_tx.c

@@ -274,6 +274,13 @@ int mcp25xxfd_can_tx_handle_int_tefif_fifo(struct mcp25xxfd_can_priv *cpriv)
  MCP25XXFD_CAN_TEFCON_UINC);
 }
 
+/* reading TEF entries can be made even more efficient by reading
+ * multiple TEF entries in one go.
+ * Under the assumption that we have count(TEF) >= count(TX_FIFO)
+ * we can even release TEFs early (before we read them)
+ * (and potentially restarting the transmit-queue early aswell)
+ */
+
 static int
 mcp25xxfd_can_tx_handle_int_tefif_conservative(struct mcp25xxfd_can_priv *cpriv)
 {
@@ -304,6 +311,25 @@ mcp25xxfd_can_tx_handle_int_tefif_conservative(struct mcp25xxfd_can_priv *cpriv)
  return 0;
 }
 
+static int
+mcp25xxfd_can_tx_handle_int_tefif_optimized(struct mcp25xxfd_can_priv *cpriv,
+ u32 finished)
+{
+ int i, fifo, ret;
+
+ /* now iterate those */
+ for (i = 0, fifo = cpriv->fifos.tx.start; i < cpriv->fifos.tx.count;
+ i++, fifo++) {
+ if (finished & BIT(fifo)) {
+ ret = mcp25xxfd_can_tx_handle_int_tefif_fifo(cpriv);
+ if (ret)
+ return ret;
+ }
+ }
+
+ return 0;
+}
+
 int mcp25xxfd_can_tx_handle_int_tefif(struct mcp25xxfd_can_priv *cpriv)
 {
  unsigned long flags;
@@ -323,6 +349,13 @@ int mcp25xxfd_can_tx_handle_int_tefif(struct mcp25xxfd_can_priv *cpriv)
 
  spin_unlock_irqrestore(&cpriv->fifos.tx_queue->lock, flags);
 
+ /* run in optimized mode if possible */
+ if (finished)
+ return mcp25xxfd_can_tx_handle_int_tefif_optimized(cpriv,
+ finished);
+ /* otherwise play it safe */
+ netdev_warn(cpriv->can.dev,
+ "Something is wrong - we got a TEF interrupt but we were not able to detect a finished fifo\n");
  return mcp25xxfd_can_tx_handle_int_tefif_conservative(cpriv);
 }