spi: spi-imx: Fix spi_bus_clk if requested clock is higher than input clock

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2071848
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2122415

commit db2d2dc
Author: Frieder Schrempf <frieder.schrempf@kontron.de>
Date: Tue, 15 Nov 2022 19:10:00 +0100

    In case the requested bus clock is higher than the input clock, the correct
    dividers (pre = 0, post = 0) are returned from mx51_ecspi_clkdiv(), but
    *fres is left uninitialized and therefore contains an arbitrary value.

    This causes trouble for the recently introduced PIO polling feature as the
    value in spi_imx->spi_bus_clk is used there to calculate for which
    transfers to enable PIO polling.

    Fix this by setting *fres even if no clock dividers are in use.

    This issue was observed on Kontron BL i.MX8MM with an SPI peripheral clock set
    to 50 MHz by default and a requested SPI bus clock of 80 MHz for the SPI NOR
    flash.

    With the fix applied the debug message from mx51_ecspi_clkdiv() now prints the
    following:

    spi_imx 30820000.spi: mx51_ecspi_clkdiv: fin: 50000000, fspi: 50000000,
    post: 0, pre: 0

    Fixes: 6fd8b85 ("spi: spi-imx: Fix out-of-order CS/SCLK operation at low speeds")
    Fixes: 07e7593 ("spi: spi-imx: add PIO polling support")
    Cc: Marc Kleine-Budde <mkl@pengutronix.de>
    Cc: David Jander <david@protonic.nl>
    Cc: Fabio Estevam <festevam@gmail.com>
    Cc: Mark Brown <broonie@kernel.org>
    Cc: Marek Vasut <marex@denx.de>
    Cc: stable@vger.kernel.org
    Signed-off-by: Frieder Schrempf <frieder.schrempf@kontron.de>
    Tested-by: Fabio Estevam <festevam@gmail.com>
    Acked-by: Marek Vasut <marex@denx.de>
    Link: https://lore.kernel.org/r/20221115181002.2068270-1-frieder@fris.de
    Signed-off-by: Mark Brown <broonie@kernel.org>

Signed-off-by: Mark Salter <msalter@redhat.com>

Author: mosalter

drivers/spi/spi-imx.c

@@ -444,8 +444,7 @@ static unsigned int mx51_ecspi_clkdiv(struct spi_imx_data *spi_imx,
 	unsigned int pre, post;
 	unsigned int fin = spi_imx->spi_clk;
 
-	if (unlikely(fspi > fin))
-		return 0;
+	fspi = min(fspi, fin);
 
 	post = fls(fin) - fls(fspi);
 	if (fin > fspi << post)