spi: spi-fsl-lpspi: Clamp too high speed_hz

[ Upstream commit af357a6 ]

Currently the driver is not able to handle the case that a SPI device
specifies a higher spi-max-frequency than half of per-clk:

    per-clk should be at least two times of transfer speed

Fix this by clamping to the max possible value and use the minimum SCK
period of 2 cycles.

Fixes: 77736a9 ("spi: lpspi: add the error info of transfer speed setting")
Signed-off-by: Stefan Wahren <wahrenst@gmx.net>
Link: https://patch.msgid.link/20250807100742.9917-1-wahrenst@gmx.net
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: lategoodbye

drivers/spi/spi-fsl-lpspi.c

@@ -331,13 +331,11 @@ static int fsl_lpspi_set_bitrate(struct fsl_lpspi_data *fsl_lpspi)
 	}
 
 	if (config.speed_hz > perclk_rate / 2) {
-		dev_err(fsl_lpspi->dev,
-		      "per-clk should be at least two times of transfer speed");
-		return -EINVAL;
+		div = 2;
+	} else {
+		div = DIV_ROUND_UP(perclk_rate, config.speed_hz);
 	}
 
-	div = DIV_ROUND_UP(perclk_rate, config.speed_hz);
-
 	for (prescale = 0; prescale <= prescale_max; prescale++) {
 		scldiv = div / (1 << prescale) - 2;
 		if (scldiv >= 0 && scldiv < 256) {