[PATCH v2] ASoC: RT5677-SPI: Disable 16Bit SPI Transfers

[Curtis Malainey <cujomalainey@chromium.org>]

The current algorithm allows 3 types of transfers, 16bit, 32bit and
burst. According to Realtek, 16bit transfers have a special restriction
in that it is restricted to the memory region of
0x18020000 ~ 0x18021000. This region is the memory location of the I2C
registers. The current algorithm does not uphold this restriction and
therefore fails to complete writes.

Since this has been broken for some time it likely no one is using it.
Better to simply disable the 16 bit writes. This will allow users to
properly load firmware over SPI without data corruption.

CC: Ben Zhang <benzh@chromium.org>
CC: Oder Chiou <oder_chiou@realtek.com>
Signed-off-by: Curtis Malainey <cujomalainey@chromium.org>
---
 sound/soc/codecs/rt5677-spi.c | 35 ++++++++++++++++-------------------
 1 file changed, 16 insertions(+), 19 deletions(-)

diff --git a/sound/soc/codecs/rt5677-spi.c b/sound/soc/codecs/rt5677-spi.c
index 167a02773a0b..84b6bd8b50e1 100644
--- a/sound/soc/codecs/rt5677-spi.c
+++ b/sound/soc/codecs/rt5677-spi.c
@@ -58,13 +58,15 @@ static DEFINE_MUTEX(spi_mutex);
  * RT5677_SPI_READ/WRITE_32:	Transfer 4 bytes
  * RT5677_SPI_READ/WRITE_BURST:	Transfer any multiples of 8 bytes
  *
- * For example, reading 260 bytes at 0x60030002 uses the following commands:
- * 0x60030002 RT5677_SPI_READ_16	2 bytes
+ * Note:
+ * 16 Bit writes and reads are restricted to the address range
+ * 0x18020000 ~ 0x18021000
+ *
+ * For example, reading 256 bytes at 0x60030004 uses the following commands:
  * 0x60030004 RT5677_SPI_READ_32	4 bytes
  * 0x60030008 RT5677_SPI_READ_BURST	240 bytes
  * 0x600300F8 RT5677_SPI_READ_BURST	8 bytes
  * 0x60030100 RT5677_SPI_READ_32	4 bytes
- * 0x60030104 RT5677_SPI_READ_16	2 bytes
  *
  * Input:
  * @read: true for read commands; false for write commands
@@ -79,15 +81,13 @@ static u8 rt5677_spi_select_cmd(bool read, u32 align, u32 remain, u32 *len)
 {
 	u8 cmd;
 
-	if (align == 2 || align == 6 || remain == 2) {
-		cmd = RT5677_SPI_READ_16;
-		*len = 2;
-	} else if (align == 4 || remain <= 6) {
+	if (align == 4 || remain <= 4) {
 		cmd = RT5677_SPI_READ_32;
 		*len = 4;
 	} else {
 		cmd = RT5677_SPI_READ_BURST;
-		*len = min_t(u32, remain & ~7, RT5677_SPI_BURST_LEN);
+		*len = (((remain - 1) >> 3) + 1) << 3;
+		*len = min_t(u32, *len, RT5677_SPI_BURST_LEN);
 	}
 	return read ? cmd : cmd + 1;
 }
@@ -108,7 +108,7 @@ static void rt5677_spi_reverse(u8 *dst, u32 dstlen, const u8 *src, u32 srclen)
 	}
 }
 
-/* Read DSP address space using SPI. addr and len have to be 2-byte aligned. */
+/* Read DSP address space using SPI. addr and len have to be 4-byte aligned. */
 int rt5677_spi_read(u32 addr, void *rxbuf, size_t len)
 {
 	u32 offset;
@@ -124,7 +124,7 @@ int rt5677_spi_read(u32 addr, void *rxbuf, size_t len)
 	if (!g_spi)
 		return -ENODEV;
 
-	if ((addr & 1) || (len & 1)) {
+	if ((addr & 3) || (len & 3)) {
 		dev_err(&g_spi->dev, "Bad read align 0x%x(%zu)\n", addr, len);
 		return -EACCES;
 	}
@@ -159,13 +159,13 @@ int rt5677_spi_read(u32 addr, void *rxbuf, size_t len)
 }
 EXPORT_SYMBOL_GPL(rt5677_spi_read);
 
-/* Write DSP address space using SPI. addr has to be 2-byte aligned.
- * If len is not 2-byte aligned, an extra byte of zero is written at the end
+/* Write DSP address space using SPI. addr has to be 4-byte aligned.
+ * If len is not 4-byte aligned, then extra zeros are written at the end
  * as padding.
  */
 int rt5677_spi_write(u32 addr, const void *txbuf, size_t len)
 {
-	u32 offset, len_with_pad = len;
+	u32 offset;
 	int status = 0;
 	struct spi_transfer t;
 	struct spi_message m;
@@ -178,22 +178,19 @@ int rt5677_spi_write(u32 addr, const void *txbuf, size_t len)
 	if (!g_spi)
 		return -ENODEV;
 
-	if (addr & 1) {
+	if (addr & 3) {
 		dev_err(&g_spi->dev, "Bad write align 0x%x(%zu)\n", addr, len);
 		return -EACCES;
 	}
 
-	if (len & 1)
-		len_with_pad = len + 1;
-
 	memset(&t, 0, sizeof(t));
 	t.tx_buf = buf;
 	t.speed_hz = RT5677_SPI_FREQ;
 	spi_message_init_with_transfers(&m, &t, 1);
 
-	for (offset = 0; offset < len_with_pad;) {
+	for (offset = 0; offset < len;) {
 		spi_cmd = rt5677_spi_select_cmd(false, (addr + offset) & 7,
-				len_with_pad - offset, &t.len);
+				len - offset, &t.len);
 
 		/* Construct SPI message header */
 		buf[0] = spi_cmd;
-- 
2.21.0.1020.gf2820cf01a-goog