[PATCH 2/3] drm/tiny: ili9486: Do not assume 8-bit only SPI controllers

[Carlo Caione <ccaione@xxxxxxxxxxxx>]

The ILI9486 driver is wrongly assuming that the SPI panel is interfaced
only with 8-bit SPI controllers and consequently that the pixel data
passed by the MIPI DBI subsystem are already swapped before being sent
over SPI using 8 bits-per-word.

This is not always true for all the SPI controllers.

Make the command function more general to not only support 8-bit only
SPI controllers and support sending un-swapped data over SPI using 16
bits-per-word when dealing with pixel data.

Signed-off-by: Carlo Caione <ccaione@xxxxxxxxxxxx>
---
 drivers/gpu/drm/tiny/ili9486.c | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/tiny/ili9486.c b/drivers/gpu/drm/tiny/ili9486.c
index bd37dfe8dd05..4d80a413338f 100644
--- a/drivers/gpu/drm/tiny/ili9486.c
+++ b/drivers/gpu/drm/tiny/ili9486.c
@@ -43,6 +43,7 @@ static int waveshare_command(struct mipi_dbi *mipi, u8 *cmd, u8 *par,
 			     size_t num)
 {
 	struct spi_device *spi = mipi->spi;
+	unsigned int bpw = 8;
 	void *data = par;
 	u32 speed_hz;
 	int i, ret;
@@ -56,8 +57,6 @@ static int waveshare_command(struct mipi_dbi *mipi, u8 *cmd, u8 *par,
 	 * The displays are Raspberry Pi HATs and connected to the 8-bit only
 	 * SPI controller, so 16-bit command and parameters need byte swapping
 	 * before being transferred as 8-bit on the big endian SPI bus.
-	 * Pixel data bytes have already been swapped before this function is
-	 * called.
 	 */
 	buf[0] = cpu_to_be16(*cmd);
 	gpiod_set_value_cansleep(mipi->dc, 0);
@@ -71,12 +70,18 @@ static int waveshare_command(struct mipi_dbi *mipi, u8 *cmd, u8 *par,
 		for (i = 0; i < num; i++)
 			buf[i] = cpu_to_be16(par[i]);
 		num *= 2;
-		speed_hz = mipi_dbi_spi_cmd_max_speed(spi, num);
 		data = buf;
 	}
 
+	/*
+	 * Check whether pixel data bytes needs to be swapped or not
+	 */
+	if (*cmd == MIPI_DCS_WRITE_MEMORY_START && !mipi->swap_bytes)
+		bpw = 16;
+
 	gpiod_set_value_cansleep(mipi->dc, 1);
-	ret = mipi_dbi_spi_transfer(spi, speed_hz, 8, data, num);
+	speed_hz = mipi_dbi_spi_cmd_max_speed(spi, num);
+	ret = mipi_dbi_spi_transfer(spi, speed_hz, bpw, data, num);
  free:
 	kfree(buf);
 

-- 
b4 0.10.1