spi: omap2-mcspi: Revert multi mode support

There have been multiple reports that the multi-mode support in the
OMAP2 McSPI driver has caused regressions on existing systems.  There's
been some discussion and some proposed changes but nothing that's been
tested by all the reporters.  Drop the patch for v6.10, hopefully we can
get to the bottom of the issue and reenable the feature for v6.11.

Reported-by: Colin Foster <colin.foster@in-advantage.com>
Reported-by: João Paulo Gonçalves <jpaulo.silvagoncalves@gmail.com>
Fixes: e64d3b6 ("spi: omap2-mcpsi: Enable MULTI-mode in more situations")
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://patch.msgid.link/20240704-spi-revert-omap2-multi-v1-1-69357ef13fdc@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: broonie

drivers/spi/spi-omap2-mcspi.c

@@ -1277,24 +1277,11 @@ static int omap2_mcspi_prepare_message(struct spi_controller *ctlr,
 
 		/*
 		 * Check if this transfer contains only one word;
-		 * OR contains 1 to 4 words, with bits_per_word == 8 and no delay between each word
-		 * OR contains 1 to 2 words, with bits_per_word == 16 and no delay between each word
-		 *
-		 * If one of the two last case is true, this also change the bits_per_word of this
-		 * transfer to make it a bit faster.
-		 * It's not an issue to change the bits_per_word here even if the multi-mode is not
-		 * applicable for this message, the signal on the wire will be the same.
 		 */
 		if (bits_per_word < 8 && tr->len == 1) {
 			/* multi-mode is applicable, only one word (1..7 bits) */
-		} else if (tr->word_delay.value == 0 && bits_per_word == 8 && tr->len <= 4) {
-			/* multi-mode is applicable, only one "bigger" word (8,16,24,32 bits) */
-			tr->bits_per_word = tr->len * bits_per_word;
-		} else if (tr->word_delay.value == 0 && bits_per_word == 16 && tr->len <= 2) {
-			/* multi-mode is applicable, only one "bigger" word (16,32 bits) */
-			tr->bits_per_word = tr->len * bits_per_word / 2;
 		} else if (bits_per_word >= 8 && tr->len == bits_per_word / 8) {
-			/* multi-mode is applicable, only one word (9..15,17..32 bits) */
+			/* multi-mode is applicable, only one word (8..32 bits) */
 		} else {
 			/* multi-mode is not applicable: more than one word in the transfer */
 			mcspi->use_multi_mode = false;