Re: [PATCH] spi: orion: support armada extended baud rates

[Jonas Gorski <jogo@xxxxxxxxxxx>]

On Mon, Sep 1, 2014 at 9:01 AM,  <gerg@xxxxxxxxxxx> wrote:
> From: Greg Ungerer <gerg@xxxxxxxxxxx>
>
> The Armada SoC family implementation of this SPI hardware module has
> extended the configuration register to allow for a wider range of SPI
> clock rates. Specifically the Serial Baud Rate Pre-selection bits in the
> SPI Interface Configuration Register now also use bits 6 and 7 as well.
>
> Modify the baud rate calculation to handle these differences for the
> Armada case. Potentially a baud rate can be setup using a number of
> different pre-scalar and scalar combinations. This code tries all
> possible pre-scalar divisors (8 in total) to try and find the most
> accuate set.
>
> Signed-off-by: Greg Ungerer <gerg@xxxxxxxxxxx>
> ---
>  drivers/spi/spi-orion.c | 77 +++++++++++++++++++++++++++++++++++++++----------
>  1 file changed, 61 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/spi/spi-orion.c b/drivers/spi/spi-orion.c
> index c4675fa..816822f 100644
> --- a/drivers/spi/spi-orion.c
> +++ b/drivers/spi/spi-orion.c
> @@ -40,6 +40,7 @@
>  #define ORION_SPI_MODE_CPHA            (1 << 12)
>  #define ORION_SPI_IF_8_16_BIT_MODE     (1 << 5)
>  #define ORION_SPI_CLK_PRESCALE_MASK    0x1F
> +#define ARMADA_SPI_CLK_PRESCALE_MASK   0xDF
>  #define ORION_SPI_MODE_MASK            (ORION_SPI_MODE_CPOL | \
>                                          ORION_SPI_MODE_CPHA)
>
> @@ -82,31 +83,74 @@ static int orion_spi_baudrate_set(struct spi_device *spi, unsigned int speed)
>         u32 rate;
>         u32 prescale;
>         u32 reg;
> +       u32 mask;
>         struct orion_spi *orion_spi;
>
>         orion_spi = spi_master_get_devdata(spi->master);
>
>         tclk_hz = clk_get_rate(orion_spi->clk);
>
> -       /*
> -        * the supported rates are: 4,6,8...30
> -        * round up as we look for equal or less speed
> -        */
> -       rate = DIV_ROUND_UP(tclk_hz, speed);
> -       rate = roundup(rate, 2);
> +       if (of_machine_is_compatible("marvell,armada370")) {

This is ugly, can't you use a new compatible name for the driver (e.g.
"marvell,armada370-spi")? And then just store the result in orion_spi.
I don't think checking a compatible string for every transfer is good
for performance. Also what about armada370-xp, armada375, armada380
and any other variants out there?

> +               unsigned int clk, spr, sppr, sppr2, err;
> +               unsigned int best_spr, best_sppr, best_err;
>
> -       /* check if requested speed is too small */
> -       if (rate > 30)
> -               return -EINVAL;
> +               best_err = speed;
> +               best_spr = 0;
> +               best_sppr = 0;
>
> -       if (rate < 4)
> -               rate = 4;
> +               tclk_hz *= 10;
> +               if (speed > tclk_hz)
> +                       return -EINVAL;
>
> -       /* Convert the rate to SPI clock divisor value. */
> -       prescale = 0x10 + rate/2;
> +               /* Iterate over the valid range looking for best fit */
> +               for (sppr = 0; sppr < 8; sppr++) {
> +                       sppr2 = 0x1 << sppr;
> +
> +                       spr = tclk_hz / sppr2;
> +                       spr = DIV_ROUND_UP(spr, speed);
> +                       if ((spr == 0) || (spr > 15))
> +                               continue;
> +
> +                       clk = tclk_hz / (spr * sppr2);
> +                       err = speed - clk;
> +
> +                       if (err < best_err) {
> +                               best_spr = spr;
> +                               best_sppr = sppr;
> +                               best_err = err;
> +                       }
> +               }
> +
> +               if ((best_sppr == 0) && (best_spr == 0))
> +                       return -EINVAL;
> +
> +               prescale = ((best_sppr & 0x6) << 5) |
> +                       ((best_sppr & 0x1) << 4) | best_spr;
> +
> +               mask = ARMADA_SPI_CLK_PRESCALE_MASK;
> +       } else {
> +               mask = ORION_SPI_CLK_PRESCALE_MASK;
> +
> +               /*
> +                * the supported rates are: 4,6,8...30
> +                * round up as we look for equal or less speed
> +                */
> +               rate = DIV_ROUND_UP(tclk_hz, speed);
> +               rate = roundup(rate, 2);
> +
> +               /* check if requested speed is too small */
> +               if (rate > 30)
> +                       return -EINVAL;
> +
> +               if (rate < 4)
> +                       rate = 4;
> +
> +               /* Convert the rate to SPI clock divisor value. */
> +               prescale = 0x10 + rate/2;
> +       }
>
>         reg = readl(spi_reg(orion_spi, ORION_SPI_IF_CONFIG_REG));
> -       reg = ((reg & ~ORION_SPI_CLK_PRESCALE_MASK) | prescale);
> +       reg = ((reg & ~mask) | prescale);
>         writel(reg, spi_reg(orion_spi, ORION_SPI_IF_CONFIG_REG));
>
>         return 0;
> @@ -348,7 +392,7 @@ static int orion_spi_probe(struct platform_device *pdev)
>         struct orion_spi *spi;
>         struct resource *r;
>         unsigned long tclk_hz;
> -       int status = 0;
> +       int mindiv, status = 0;
>
>         master = spi_alloc_master(&pdev->dev, sizeof(*spi));
>         if (master == NULL) {
> @@ -390,7 +434,8 @@ static int orion_spi_probe(struct platform_device *pdev)
>
>         tclk_hz = clk_get_rate(spi->clk);
>         master->max_speed_hz = DIV_ROUND_UP(tclk_hz, 4);
> -       master->min_speed_hz = DIV_ROUND_UP(tclk_hz, 30);
> +       mindiv = (of_machine_is_compatible("marvell,armada370")) ? 1920 : 30;

Same as above.


Jonas
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