net: ethernet: oa_tc6: implement transmit path to transfer tx ethernet frames

The transmit ethernet frame will be converted into multiple transmit data
chunks. Each transmit data chunk consists of a 4 bytes header followed by
a 64 bytes transmit data chunk payload. The 4 bytes data header occurs at
the beginning of each transmit data chunk on MOSI. The data header
contains the information needed to determine the validity and location of
the transmit frame data within the data chunk payload. The number of
transmit data chunks transmitted to mac-phy is limited to the number
transmit credits available in the mac-phy. Initially the transmit credits
will be updated from the buffer status register and then it will be
updated from the footer received on each spi data transfer. The received
footer will be examined for the transmit errors if any.
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Parthiban Veerasooran <Parthiban.Veerasooran@microchip.com>
Link: https://patch.msgid.link/20240909082514.262942-10-Parthiban.Veerasooran@microchip.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

include/linux/oa_tc6.h

@@ -20,3 +20,4 @@ int oa_tc6_write_registers(struct oa_tc6 *tc6, u32 address, u32 value[],
 int oa_tc6_read_register(struct oa_tc6 *tc6, u32 address, u32 *value);
 int oa_tc6_read_registers(struct oa_tc6 *tc6, u32 address, u32 value[],
 			  u8 length);
+netdev_tx_t oa_tc6_start_xmit(struct oa_tc6 *tc6, struct sk_buff *skb);