Re: [PATCH v2 5/5] spi: bcm-mspi: Add support to set serial baud clock rate

[Jonas Gorski <jogo@xxxxxxxxxxx>]

Hi,

On Wed, Apr 8, 2015 at 8:04 PM, Jonathan Richardson
<jonathar@xxxxxxxxxxxx> wrote:
> The driver wasn't setting the SPBR (serial clock baud rate) which caused
> it to run at the slowest speed possible. The driver now calculates the
> SPBR based on the reference clock frequency resulting in much faster
> SPI transfers.
>
> Signed-off-by: Jonathan Richardson <jonathar@xxxxxxxxxxxx>
> ---
>  drivers/spi/spi-bcm-mspi.c |   50 ++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
>
> diff --git a/drivers/spi/spi-bcm-mspi.c b/drivers/spi/spi-bcm-mspi.c
> index 32bb1f0..9320de9 100644
> --- a/drivers/spi/spi-bcm-mspi.c
> +++ b/drivers/spi/spi-bcm-mspi.c
> @@ -18,10 +18,15 @@
>  #include <linux/bcma/bcma.h>
>  #include <linux/spi/spi.h>
>  #include <linux/of.h>
> +#include <linux/clk.h>
>
>  #include "spi-bcm-mspi.h"
>
>  #define BCM_MSPI_MAX_SPI_BAUD   13500000       /* 216 MHz? */
> +#define SPBR_MIN                8U
> +#define SPBR_MAX                255U
> +#define MSPI_SPCR0_LSB_OFFSET   0x200
> +#define MSPI_SPCR0_LSB_SHIFT    0
>
>  /* The longest observed required wait was 19 ms */
>  #define BCM_MSPI_SPE_TIMEOUT_MS 80
> @@ -33,7 +38,9 @@ struct bcm_mspi {
>
>         void __iomem *base;
>         struct spi_master *master;
> +       struct clk *clk;
>         size_t read_offset;
> +       u32    spbr;
>
>         void (*mspi_write)(struct bcm_mspi *mspi, u16 offset, u32 value);
>         u32 (*mspi_read)(struct bcm_mspi *mspi, u16 offset);
> @@ -45,6 +52,15 @@ static inline unsigned int bcm_mspi_calc_timeout(size_t len)
>         return (len * 9000 / BCM_MSPI_MAX_SPI_BAUD * 110 / 100) + 1;
>  }
>
> +static void bcm_mspi_hw_init(struct bcm_mspi *mspi)
> +{
> +       /* Set SPBR (serial clock baud rate). */
> +       if (mspi->spbr) {
> +               mspi->mspi_write(mspi, MSPI_SPCR0_LSB_OFFSET,
> +                       mspi->spbr << MSPI_SPCR0_LSB_SHIFT);
> +       }
> +}
> +
>  static int bcm_mspi_wait(struct bcm_mspi *mspi, unsigned int timeout_ms)
>  {
>         unsigned long deadline;
> @@ -222,6 +238,7 @@ static struct bcm_mspi *bcm_mspi_init(struct device *dev)
>  {
>         struct bcm_mspi *data;
>         struct spi_master *master;
> +       u32 desired_rate;
>
>         master = spi_alloc_master(dev, sizeof(*data));
>         if (!master) {
> @@ -236,6 +253,33 @@ static struct bcm_mspi *bcm_mspi_init(struct device *dev)
>         master->dev.of_node = dev->of_node;
>         master->transfer_one = bcm_mspi_transfer_one;
>
> +       /*
> +        * Enable clock if provided. The frequency can be changed by setting
> +        * SPBR (serial clock baud rate) based on the desired 'clock-frequency'.
> +        *
> +        * Baud rate is calculated as: mspi_clk / (2 * SPBR) where SPBR is a
> +        * value between 1-255. If not set then it is left at the h/w default.
> +        */
> +       data->clk = devm_clk_get(dev, "mspi_clk");
> +       if (!IS_ERR(data->clk)) {
> +               int ret = clk_prepare_enable(data->clk);

You need to disable_unprepare the clock on removal, I don't see you doing that.

> +
> +               if (ret < 0) {
> +                       dev_err(dev, "failed to enable clock: %d\n", ret);
> +                       return 0;
> +               }
> +
> +               /* Calculate SPBR if clock-frequency provided. */
> +               if (of_property_read_u32(dev->of_node, "clock-frequency",
> +                       &desired_rate) >= 0) {
> +                       u32 spbr = clk_get_rate(data->clk) / (2 * desired_rate);
> +
> +                       if (spbr > 0)
> +                               data->spbr = clamp_val(spbr, SPBR_MIN,
> +                                       SPBR_MAX);
> +               }
> +       }
> +
>         return data;
>  }
>
> @@ -287,6 +331,9 @@ static int bcm_mspi_probe(struct platform_device *pdev)
>         data->mspi_write = bcm_mspi_write;
>         platform_set_drvdata(pdev, data);
>
> +       /* Initialize SPI controller. */
> +       bcm_mspi_hw_init(data);
> +
>         err = devm_spi_register_master(dev, data->master);
>         if (err)
>                 goto out;
> @@ -362,6 +409,9 @@ static int bcm_mspi_bcma_probe(struct bcma_device *core)
>
>         bcma_set_drvdata(core, data);
>
> +       /* Initialize SPI controller. */
> +       bcm_mspi_hw_init(data);
> +
>         err = devm_spi_register_master(&core->dev, data->master);
>         if (err) {
>                 spi_master_put(data->master);
> --

Regards
Jonas
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