Re: [PATCH v3 3/5] spi: sun6i: add quirk for in-controller clock divider

[Andre Przywara <andre.przywara@xxxxxxx>]

On Sun,  7 May 2023 02:26:06 +0300
Maksim Kiselev <bigunclemax@xxxxxxxxx> wrote:

Hi Maksim,

thanks for the quick turnaround and the changes.

> Previously SPI controllers in Allwinner SoCs has a clock divider inside.
> However now the clock divider is removed and to set the transfer clock
> rate it's only needed to set the SPI module clock to the target value
> and configure a proper work mode.
> 
> According to the datasheet there are three work modes:
> 
> | SPI Sample Mode         | SDM(bit13) | SDC(bit11) | Run Clock |
> |-------------------------|------------|------------|-----------|
> | normal sample           |      1     |      0     | <= 24 MHz |
> | delay half cycle sample |      0     |      0     | <= 40 MHz |
> | delay one cycle sample  |      0     |      1     | >= 80 MHz |
> 
> Add a quirk for this kind of SPI controllers.
> 
> Co-developed-by: Icenowy Zheng <icenowy@xxxxxxx>
> Signed-off-by: Maksim Kiselev <bigunclemax@xxxxxxxxx>
> ---
>  drivers/spi/spi-sun6i.c | 92 +++++++++++++++++++++++++++--------------
>  1 file changed, 62 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/spi/spi-sun6i.c b/drivers/spi/spi-sun6i.c
> index 01a01cd86db5..1e9e9a8159d9 100644
> --- a/drivers/spi/spi-sun6i.c
> +++ b/drivers/spi/spi-sun6i.c
> @@ -42,7 +42,9 @@
>  #define SUN6I_TFR_CTL_CS_MANUAL			BIT(6)
>  #define SUN6I_TFR_CTL_CS_LEVEL			BIT(7)
>  #define SUN6I_TFR_CTL_DHB			BIT(8)
> +#define SUN6I_TFR_CTL_SDC			BIT(11)
>  #define SUN6I_TFR_CTL_FBS			BIT(12)
> +#define SUN6I_TFR_CTL_SDM			BIT(13)
>  #define SUN6I_TFR_CTL_XCH			BIT(31)
>  
>  #define SUN6I_INT_CTL_REG		0x10
> @@ -87,6 +89,7 @@
>  
>  struct sun6i_spi_cfg {
>  	unsigned long		fifo_depth;
> +	bool			has_clk_ctl;
>  };
>  
>  struct sun6i_spi {
> @@ -260,7 +263,7 @@ static int sun6i_spi_transfer_one(struct spi_master *master,
>  				  struct spi_transfer *tfr)
>  {
>  	struct sun6i_spi *sspi = spi_master_get_devdata(master);
> -	unsigned int mclk_rate, div, div_cdr1, div_cdr2, timeout;
> +	unsigned int div, div_cdr1, div_cdr2, timeout;
>  	unsigned int start, end, tx_time;
>  	unsigned int trig_level;
>  	unsigned int tx_len = 0, rx_len = 0;
> @@ -350,39 +353,66 @@ static int sun6i_spi_transfer_one(struct spi_master *master,
>  
>  	sun6i_spi_write(sspi, SUN6I_TFR_CTL_REG, reg);
>  
> -	/* Ensure that we have a parent clock fast enough */
> -	mclk_rate = clk_get_rate(sspi->mclk);
> -	if (mclk_rate < (2 * tfr->speed_hz)) {
> -		clk_set_rate(sspi->mclk, 2 * tfr->speed_hz);
> -		mclk_rate = clk_get_rate(sspi->mclk);
> -	}
> +	if (sspi->cfg->has_clk_ctl) {
> +		unsigned int mclk_rate = clk_get_rate(sspi->mclk);
>  
> -	/*
> -	 * Setup clock divider.
> -	 *
> -	 * We have two choices there. Either we can use the clock
> -	 * divide rate 1, which is calculated thanks to this formula:
> -	 * SPI_CLK = MOD_CLK / (2 ^ cdr)
> -	 * Or we can use CDR2, which is calculated with the formula:
> -	 * SPI_CLK = MOD_CLK / (2 * (cdr + 1))
> -	 * Wether we use the former or the latter is set through the
> -	 * DRS bit.
> -	 *
> -	 * First try CDR2, and if we can't reach the expected
> -	 * frequency, fall back to CDR1.
> -	 */
> -	div_cdr1 = DIV_ROUND_UP(mclk_rate, tfr->speed_hz);
> -	div_cdr2 = DIV_ROUND_UP(div_cdr1, 2);
> -	if (div_cdr2 <= (SUN6I_CLK_CTL_CDR2_MASK + 1)) {
> -		reg = SUN6I_CLK_CTL_CDR2(div_cdr2 - 1) | SUN6I_CLK_CTL_DRS;
> -		tfr->effective_speed_hz = mclk_rate / (2 * div_cdr2);
> +		/* Ensure that we have a parent clock fast enough */
> +		if (mclk_rate < (2 * tfr->speed_hz)) {
> +			clk_set_rate(sspi->mclk, 2 * tfr->speed_hz);
> +			mclk_rate = clk_get_rate(sspi->mclk);
> +		}
> +
> +		/*
> +		 * Setup clock divider.
> +		 *
> +		 * We have two choices there. Either we can use the clock
> +		 * divide rate 1, which is calculated thanks to this formula:
> +		 * SPI_CLK = MOD_CLK / (2 ^ cdr)
> +		 * Or we can use CDR2, which is calculated with the formula:
> +		 * SPI_CLK = MOD_CLK / (2 * (cdr + 1))
> +		 * Whether we use the former or the latter is set through the
> +		 * DRS bit.
> +		 *
> +		 * First try CDR2, and if we can't reach the expected
> +		 * frequency, fall back to CDR1.
> +		 */
> +		div_cdr1 = DIV_ROUND_UP(mclk_rate, tfr->speed_hz);
> +		div_cdr2 = DIV_ROUND_UP(div_cdr1, 2);
> +		if (div_cdr2 <= (SUN6I_CLK_CTL_CDR2_MASK + 1)) {
> +			reg = SUN6I_CLK_CTL_CDR2(div_cdr2 - 1) | SUN6I_CLK_CTL_DRS;
> +			tfr->effective_speed_hz = mclk_rate / (2 * div_cdr2);
> +		} else {
> +			div = min(SUN6I_CLK_CTL_CDR1_MASK, order_base_2(div_cdr1));
> +			reg = SUN6I_CLK_CTL_CDR1(div);
> +			tfr->effective_speed_hz = mclk_rate / (1 << div);
> +		}
> +
> +		sun6i_spi_write(sspi, SUN6I_CLK_CTL_REG, reg);
>  	} else {
> -		div = min(SUN6I_CLK_CTL_CDR1_MASK, order_base_2(div_cdr1));
> -		reg = SUN6I_CLK_CTL_CDR1(div);
> -		tfr->effective_speed_hz = mclk_rate / (1 << div);
> +		clk_set_rate(sspi->mclk, tfr->speed_hz);
> +		tfr->effective_speed_hz = clk_get_rate(sspi->mclk);
> +
> +		/*
> +		 * Configure work mode.
> +		 *
> +		 * There are three work modes depending on the controller clock
> +		 * frequency:
> +		 * - normal sample mode           : CLK <= 24MHz SDM=1 SDC=0
> +		 * - delay half-cycle sample mode : CLK <= 40MHz SDM=0 SDC=0
> +		 * - delay one-cycle sample mode  : CLK >= 80MHz SDM=0 SDC=1
> +		 */
> +		reg = sun6i_spi_read(sspi, SUN6I_TFR_CTL_REG);
> +
> +		if (tfr->effective_speed_hz <= 24000000)
> +			reg |= SUN6I_TFR_CTL_SDM;
> +		else if (tfr->effective_speed_hz >= 80000000)
> +			reg |= SUN6I_TFR_CTL_SDC;

This case assumes that the SDM bit is zero already. I think just
masking both bits off above, right after the read, is the easiest, then
you can also lose the else branch below entirely.

Cheers,
Andre

> +		else
> +			reg &= ~(SUN6I_TFR_CTL_SDM | SUN6I_TFR_CTL_SDC);
> +
> +		sun6i_spi_write(sspi, SUN6I_TFR_CTL_REG, reg);
>  	}
>  
> -	sun6i_spi_write(sspi, SUN6I_CLK_CTL_REG, reg);
>  	/* Finally enable the bus - doing so before might raise SCK to HIGH */
>  	reg = sun6i_spi_read(sspi, SUN6I_GBL_CTL_REG);
>  	reg |= SUN6I_GBL_CTL_BUS_ENABLE;
> @@ -701,10 +731,12 @@ static void sun6i_spi_remove(struct platform_device *pdev)
>  
>  static const struct sun6i_spi_cfg sun6i_a31_spi_cfg = {
>  	.fifo_depth	= SUN6I_FIFO_DEPTH,
> +	.has_clk_ctl	= true,
>  };
>  
>  static const struct sun6i_spi_cfg sun8i_h3_spi_cfg = {
>  	.fifo_depth	= SUN8I_FIFO_DEPTH,
> +	.has_clk_ctl	= true,
>  };
>  
>  static const struct of_device_id sun6i_spi_match[] = {