drm/panel: s6e63m0: Add some explanations

The SPI DCS code was a bit hard to understand as the
device accepts 9-bit transfers packed into 16-bit words
with the most significant bit in bit 9 of the
16-bit word. Add some clarifying comments.
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Stephan Gerhold <stephan@gerhold.net>
Cc: Paweł Chmiel <pawel.mikolaj.chmiel@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201110234653.2248594-4-linus.walleij@linaro.org

drivers/gpu/drm/panel/panel-samsung-s6e63m0-spi.c

@@ -42,10 +42,17 @@ static int s6e63m0_spi_dcs_write(struct device *dev, const u8 *data, size_t len)
 	int ret = 0;
 
 	dev_dbg(dev, "SPI writing dcs seq: %*ph\n", (int)len, data);
+
+	/*
+	 * This sends 9 bits with the first bit (bit 8) set to 0
+	 * This indicates that this is a command. Anything after the
+	 * command is data.
+	 */
 	ret = s6e63m0_spi_write_word(dev, *data);
 
 	while (!ret && --len) {
 		++data;
+		/* This sends 9 bits with the first bit (bit 8) set to 1 */
 		ret = s6e63m0_spi_write_word(dev, *data | DATA_MASK);
 	}