linux-kernel - Re: [PATCH 3/4] spi: sun6i: add quirk for in-controller clock divider

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Message-ID: <d1c09ca7-dc25-843c-2f64-fbf5111a9118@sholland.org>
Date:   Fri, 22 Apr 2022 18:54:43 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     Icenowy Zheng <icenowy@...c.io>, Mark Brown <broonie@...nel.org>,
        Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Maxime Ripard <mripard@...nel.org>
Cc:     linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Icenowy Zheng <icenowy@...c.io>
Subject: Re: [PATCH 3/4] spi: sun6i: add quirk for in-controller clock divider

On 4/22/22 10:56 AM, icenowy@...look.com wrote:
> From: Icenowy Zheng <icenowy@...c.io>
> 
> 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.
> 
> Add a quirk for this kind of SPI controllers.
> 
> Signed-off-by: Icenowy Zheng <icenowy@...c.io>
> ---
>  drivers/spi/spi-sun6i.c | 68 +++++++++++++++++++++++------------------
>  1 file changed, 38 insertions(+), 30 deletions(-)
> 
> diff --git a/drivers/spi/spi-sun6i.c b/drivers/spi/spi-sun6i.c
> index 84c525b08ad0..fc81afc3a963 100644
> --- a/drivers/spi/spi-sun6i.c
> +++ b/drivers/spi/spi-sun6i.c
> @@ -87,6 +87,7 @@
>  
>  struct sun6i_spi_cfg {
>  	unsigned long		fifo_depth;
> +	bool			has_clk_ctl;
>  };
>  
>  struct sun6i_spi {
> @@ -260,7 +261,7 @@ 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 +351,44 @@ 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);
> +		/* 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))
> -	 * 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);
> +		/*
> +		 * 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);
> +		} 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);

clk_set_rate() may not set the exact requested rate. Should we set
tfr->effective_speed_hz based on clk_get_rate() afterward?

Regards,
Samuel

>  	}
>  
> -	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;
> @@ -702,10 +708,12 @@ static int 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[] = {
>