spi: fsl-espi: fix support for all available clock rates

According to NXP ESPI datasheet, the SPI clock rate is:

    spi_clk = System_Clock / ( 2 * DIV16 * ( 1 + PM ) )

Where System_Clock is the platform clock divided by 2,
DIV16 may be 1 or 16, and PM is a 4 bits integer (0 to 15).

Isolating PM on the expression, we get:

    PM = (System_Clock / ( 2 * DIV16 * spi_clk ) ) - 1

Where System_Clock = mpc8xxx_spi->spibrg / 2, spi_clk = hz,
and DIV16 = 1 or DIV16 = 16. So,

    PM = (mpc8xxx_spi->spibrg / ( 4 * hz) ) - 1
or
    PM = (mpc8xxx_spi->spibrg / ( 16 * 4 * hz) ) - 1

Current spi-fsl-espi driver can't configure the HW for all
supported clock rates. It filters out clock rates for PM = 0
and PM = 1.

This patch allows all range of supported clock rates to be
configured on the ESPI controller.

Signed-off-by: Paulo Zaneti <paulo.zaneti@datacom.ind.br>
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-fsl-espi.c b/drivers/spi/spi-fsl-espi.c
index 1d3c9023391d4e3799c09eaf48eb9ef99dcece53..8b3a28739d9a18ed60b91db2396214ca8c2e7a21 100644 (file)
--- a/drivers/spi/spi-fsl-espi.c
+++ b/drivers/spi/spi-fsl-espi.c
@@ -247,8 +247,7 @@ static void fsl_espi_setup_transfer(struct spi_device *spi,
 {
        struct mpc8xxx_spi *mpc8xxx_spi = spi_master_get_devdata(spi->master);
        int bits_per_word = t ? t->bits_per_word : spi->bits_per_word;
-       u32 hz = t ? t->speed_hz : spi->max_speed_hz;
-       u8 pm;
+       u32 pm, hz = t ? t->speed_hz : spi->max_speed_hz;
        struct spi_mpc8xxx_cs *cs = spi->controller_state;
 
        /* mask out bits we are going to set */
@@ -256,22 +255,19 @@ static void fsl_espi_setup_transfer(struct spi_device *spi,
 
        cs->hw_mode |= CSMODE_LEN(bits_per_word - 1);
 
-       if ((mpc8xxx_spi->spibrg / hz) > 64) {
+       pm = DIV_ROUND_UP(mpc8xxx_spi->spibrg, hz * 4) - 1;
+
+       if (pm > 15) {
                cs->hw_mode |= CSMODE_DIV16;
-               pm = DIV_ROUND_UP(mpc8xxx_spi->spibrg, hz * 16 * 4);
-
-               WARN_ONCE(pm > 33, "%s: Requested speed is too low: %d Hz. "
-                         "Will use %d Hz instead.\n", dev_name(&spi->dev),
-                               hz, mpc8xxx_spi->spibrg / (4 * 16 * (32 + 1)));
-               if (pm > 33)
-                       pm = 33;
-       } else {
-               pm = DIV_ROUND_UP(mpc8xxx_spi->spibrg, hz * 4);
+               pm = DIV_ROUND_UP(mpc8xxx_spi->spibrg, hz * 16 * 4) - 1;
+
+               WARN_ONCE(pm > 15,
+                         "%s: Requested speed is too low: %u Hz. Will use %u Hz instead.\n",
+                         dev_name(&spi->dev), hz,
+                         mpc8xxx_spi->spibrg / (4 * 16 * (15 + 1)));
+               if (pm > 15)
+                       pm = 15;
        }
-       if (pm)
-               pm--;
-       if (pm < 2)
-               pm = 2;
 
        cs->hw_mode |= CSMODE_PM(pm);