spi: fsl-espi: fix handling of word sizes other than 8 bit

The code in fsl_espi_tx_buf_lsb and parts of fsl_espi_setup_transfer
look very weird and don't reflect the ESPI spec.
ESPI stores values with <= 8 bit word size right justified as 8 bit
value and values with > 8 bit word size right justified as 16 bit
value. Therefore no such shifting is needed.
Only case MSB-first with 8 bit word size is correctly handled,
and most likely nobody ever used this driver with a different config.

On ESPI only the case LSB-first with word size > 8 bit needs a
special handling. In this case a little endian 16 bit value has
to be written to the TX FIFO what requires a byte swap as the
host system is big endian.
The same applies to reading from the RX FIFO.
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-espi.c

@@ -112,6 +112,32 @@ static inline void fsl_espi_write_reg8(struct mpc8xxx_spi *mspi, int offset,
 	iowrite8(val, mspi->reg_base + offset);
 }
 
+static void fsl_espi_memcpy_swab(void *to, const void *from,
+				 struct spi_message *m,
+				 struct spi_transfer *t)
+{
+	unsigned int len = t->len;
+
+	if (!(m->spi->mode & SPI_LSB_FIRST) || t->bits_per_word <= 8) {
+		memcpy(to, from, len);
+		return;
+	}
+
+	/* In case of LSB-first and bits_per_word > 8 byte-swap all words */
+	while (len)
+		if (len >= 4) {
+			*(u32 *)to = swahb32p(from);
+			to += 4;
+			from += 4;
+			len -= 4;
+		} else {
+			*(u16 *)to = swab16p(from);
+			to += 2;
+			from += 2;
+			len -= 2;
+		}
+}
+
 static void fsl_espi_copy_to_buf(struct spi_message *m,
 				 struct mpc8xxx_spi *mspi)
 {
@@ -120,7 +146,7 @@ static void fsl_espi_copy_to_buf(struct spi_message *m,
 
 	list_for_each_entry(t, &m->transfers, transfer_list) {
 		if (t->tx_buf)
-			memcpy(buf, t->tx_buf, t->len);
+			fsl_espi_memcpy_swab(buf, t->tx_buf, m, t);
 		else
 			memset(buf, 0, t->len);
 		buf += t->len;
@@ -135,7 +161,7 @@ static void fsl_espi_copy_from_buf(struct spi_message *m,
 
 	list_for_each_entry(t, &m->transfers, transfer_list) {
 		if (t->rx_buf)
-			memcpy(t->rx_buf, buf, t->len);
+			fsl_espi_memcpy_swab(t->rx_buf, buf, m, t);
 		buf += t->len;
 	}
 }
@@ -194,27 +220,6 @@ static void fsl_espi_change_mode(struct spi_device *spi)
 	local_irq_restore(flags);
 }
 
-static u32 fsl_espi_tx_buf_lsb(struct mpc8xxx_spi *mpc8xxx_spi)
-{
-	u32 data;
-	u16 data_h;
-	u16 data_l;
-	const u32 *tx = mpc8xxx_spi->tx;
-
-	if (!tx)
-		return 0;
-
-	data = *tx++ << mpc8xxx_spi->tx_shift;
-	data_l = data & 0xffff;
-	data_h = (data >> 16) & 0xffff;
-	swab16s(&data_l);
-	swab16s(&data_h);
-	data = data_h | data_l;
-
-	mpc8xxx_spi->tx = tx;
-	return data;
-}
-
 static void fsl_espi_setup_transfer(struct spi_device *spi,
 					struct spi_transfer *t)
 {
@@ -224,23 +229,6 @@ static void fsl_espi_setup_transfer(struct spi_device *spi,
 	u8 pm;
 	struct spi_mpc8xxx_cs *cs = spi->controller_state;
 
-	cs->rx_shift = 0;
-	cs->tx_shift = 0;
-	cs->get_rx = mpc8xxx_spi_rx_buf_u32;
-	cs->get_tx = mpc8xxx_spi_tx_buf_u32;
-	if (bits_per_word <= 8) {
-		cs->rx_shift = 8 - bits_per_word;
-	} else {
-		cs->rx_shift = 16 - bits_per_word;
-		if (spi->mode & SPI_LSB_FIRST)
-			cs->get_tx = fsl_espi_tx_buf_lsb;
-	}
-
-	mpc8xxx_spi->rx_shift = cs->rx_shift;
-	mpc8xxx_spi->tx_shift = cs->tx_shift;
-	mpc8xxx_spi->get_rx = cs->get_rx;
-	mpc8xxx_spi->get_tx = cs->get_tx;
-
 	/* mask out bits we are going to set */
 	cs->hw_mode &= ~(CSMODE_LEN(0xF) | CSMODE_DIV16 | CSMODE_PM(0xF));
 
@@ -271,7 +259,6 @@ static void fsl_espi_setup_transfer(struct spi_device *spi,
 static int fsl_espi_bufs(struct spi_device *spi, struct spi_transfer *t)
 {
 	struct mpc8xxx_spi *mpc8xxx_spi = spi_master_get_devdata(spi->master);
-	u32 word;
 	int ret;
 
 	mpc8xxx_spi->len = t->len;
@@ -290,8 +277,8 @@ static int fsl_espi_bufs(struct spi_device *spi, struct spi_transfer *t)
 	fsl_espi_write_reg(mpc8xxx_spi, ESPI_SPIM, SPIM_RNE);
 
 	/* transmit word */
-	word = mpc8xxx_spi->get_tx(mpc8xxx_spi);
-	fsl_espi_write_reg(mpc8xxx_spi, ESPI_SPITF, word);
+	fsl_espi_write_reg(mpc8xxx_spi, ESPI_SPITF, *(u32 *)mpc8xxx_spi->tx);
+	mpc8xxx_spi->tx += 4;
 
 	/* Won't hang up forever, SPI bus sometimes got lost interrupts... */
 	ret = wait_for_completion_timeout(&mpc8xxx_spi->done, 2 * HZ);
@@ -468,8 +455,10 @@ static void fsl_espi_cpu_irq(struct mpc8xxx_spi *mspi, u32 events)
 
 		mspi->len -= rx_nr_bytes;
 
-		if (mspi->rx)
-			mspi->get_rx(rx_data, mspi);
+		if (mspi->rx) {
+			*(u32 *)mspi->rx = rx_data;
+			mspi->rx += 4;
+		}
 	}
 
 	if (!(events & SPIE_TNF)) {
@@ -487,9 +476,8 @@ static void fsl_espi_cpu_irq(struct mpc8xxx_spi *mspi, u32 events)
 
 	mspi->count -= 1;
 	if (mspi->count) {
-		u32 word = mspi->get_tx(mspi);
-
-		fsl_espi_write_reg(mspi, ESPI_SPITF, word);
+		fsl_espi_write_reg(mspi, ESPI_SPITF, *(u32 *)mspi->tx);
+		mspi->tx += 4;
 	} else {
 		complete(&mspi->done);
 	}