wilc1000: Introduce symbolic names for SPI protocol register

The WILC1000 protocol control register has bits for enabling the CRCs
(CRC7 for commands and CRC16 for data) and to set the data packet
size.  Define symbolic names for those so the code is more easily
understood.
Signed-off-by: David Mosberger-Tang <davidm@egauge.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210227172818.1711071-2-davidm@egauge.net

drivers/net/wireless/microchip/wilc1000/spi.c

@@ -46,12 +46,25 @@ static const struct wilc_hif_func wilc_hif_spi;
 #define CMD_RESET				0xcf
 
 #define SPI_ENABLE_VMM_RETRY_LIMIT		2
-#define DATA_PKT_SZ_256				256
-#define DATA_PKT_SZ_512				512
-#define DATA_PKT_SZ_1K				1024
-#define DATA_PKT_SZ_4K				(4 * 1024)
-#define DATA_PKT_SZ_8K				(8 * 1024)
-#define DATA_PKT_SZ				DATA_PKT_SZ_8K
+
+#define PROTOCOL_REG_PKT_SZ_MASK		GENMASK(6, 4)
+#define PROTOCOL_REG_CRC16_MASK			GENMASK(3, 3)
+#define PROTOCOL_REG_CRC7_MASK			GENMASK(2, 2)
+
+/*
+ * The SPI data packet size may be any integer power of two in the
+ * range from 256 to 8192 bytes.
+ */
+#define DATA_PKT_LOG_SZ_MIN			8	/* 256 B */
+#define DATA_PKT_LOG_SZ_MAX			13	/* 8 KiB */
+
+/*
+ * Select the data packet size (log2 of number of bytes): Use the
+ * maximum data packet size.  We only retransmit complete packets, so
+ * there is no benefit from using smaller data packets.
+ */
+#define DATA_PKT_LOG_SZ				DATA_PKT_LOG_SZ_MAX
+#define DATA_PKT_SZ				(1 << DATA_PKT_LOG_SZ)
 
 #define USE_SPI_DMA				0
 
@@ -827,9 +840,16 @@ static int wilc_spi_init(struct wilc *wilc, bool resume)
 		}
 	}
 	if (spi_priv->crc_off == 0) {
-		reg &= ~0xc; /* disable crc checking */
-		reg &= ~0x70;
-		reg |= (0x5 << 4);
+		/* disable crc checking: */
+		reg &= ~(PROTOCOL_REG_CRC7_MASK | PROTOCOL_REG_CRC16_MASK);
+
+		/* set the data packet size: */
+		BUILD_BUG_ON(DATA_PKT_LOG_SZ < DATA_PKT_LOG_SZ_MIN
+			     || DATA_PKT_LOG_SZ > DATA_PKT_LOG_SZ_MAX);
+		reg &= ~PROTOCOL_REG_PKT_SZ_MASK;
+		reg |= FIELD_PREP(PROTOCOL_REG_PKT_SZ_MASK,
+				  DATA_PKT_LOG_SZ - DATA_PKT_LOG_SZ_MIN);
+
 		ret = spi_internal_write(wilc, WILC_SPI_PROTOCOL_OFFSET, reg);
 		if (ret) {
 			dev_err(&spi->dev,