linux-kernel - Re: [PATCH] spi: omap2-mcspi: Fix hardcoded reference clock

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Message-ID: <20230912134034.hkciu5wqiuci6hga@dhruva>
Date:   Tue, 12 Sep 2023 19:10:34 +0530
From:   Dhruva Gole <d-gole@...com>
To:     Vaishnav Achath <vaishnav.a@...com>
CC:     <broonie@...nel.org>, <linux-spi@...r.kernel.org>,
        <t-kristo@...com>, <vigneshr@...com>,
        <linux-kernel@...r.kernel.org>, <u-kumar1@...com>
Subject: Re: [PATCH] spi: omap2-mcspi: Fix hardcoded reference clock

On Sep 12, 2023 at 15:33:28 +0530, Vaishnav Achath wrote:
> A hardcoded reference clock of 48 MHz is used to calculate the
> clock divisor values, but the reference clock frequency can be
> different across devices and can be configured which can cause
> a mismatch between the reported frequency and actual SPI clock
> frequency observed. Fix this by fetching the clock rate from
> the clock provider and falling back to hardcoded reference only
> if the clock is not supplied.
> 
> Fixes: 2cd7d393f461 ("arm64: dts: ti: k3-am654: Add McSPI DT nodes")
> 
> Signed-off-by: Vaishnav Achath <vaishnav.a@...com>
> ---
> 
> Blamed commit is the first device where the default reference clock was
> different from the hardcoded value.
> Tested on TDA4VM SK (6.6.0-rc1-next-20230911)

Would be good to have some logs too next time, to share how it was tested.

> 
>  drivers/spi/spi-omap2-mcspi.c | 31 ++++++++++++++++++++-----------
>  1 file changed, 20 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/spi/spi-omap2-mcspi.c b/drivers/spi/spi-omap2-mcspi.c
> index e5cd82eb9e54..6ec45fd0e904 100644
> --- a/drivers/spi/spi-omap2-mcspi.c
> +++ b/drivers/spi/spi-omap2-mcspi.c
> @@ -125,8 +125,10 @@ struct omap2_mcspi {
>  	struct omap2_mcspi_dma	*dma_channels;
>  	struct device		*dev;
>  	struct omap2_mcspi_regs ctx;
> +	struct clk		*clk;

I dislike naming an obj after it's struct, can we come up with some
other name?

>  	int			fifo_depth;
>  	bool			slave_aborted;
> +	unsigned int		ref_clk_hz;

Do you want to make it u32 here? or...

>  	unsigned int		pin_dir:1;
>  	size_t			max_xfer_len;
>  };
> @@ -880,12 +882,12 @@ omap2_mcspi_txrx_pio(struct spi_device *spi, struct spi_transfer *xfer)
>  	return count - c;
>  }
>  
> -static u32 omap2_mcspi_calc_divisor(u32 speed_hz)
> +static u32 omap2_mcspi_calc_divisor(u32 speed_hz, u32 ref_clk_hz)

unsigned int ref_clk_hz here?

>  {
>  	u32 div;
>  
>  	for (div = 0; div < 15; div++)
> -		if (speed_hz >= (OMAP2_MCSPI_MAX_FREQ >> div))
> +		if (speed_hz >= (ref_clk_hz >> div))
>  			return div;
>  
>  	return 15;
> @@ -897,7 +899,7 @@ static int omap2_mcspi_setup_transfer(struct spi_device *spi,
>  {
>  	struct omap2_mcspi_cs *cs = spi->controller_state;
>  	struct omap2_mcspi *mcspi;
> -	u32 l = 0, clkd = 0, div, extclk = 0, clkg = 0;
> +	u32 ref_clk_hz, l = 0, clkd = 0, div, extclk = 0, clkg = 0;

here as well, your ref_clk_hz is u32 but below you're making it mcspi->ref_clk_hz
which is an unsigned int?

I know it's not a deal breaker, however not a big fan of mixing fixed
types and types that the compiler may decide.

>  	u8 word_len = spi->bits_per_word;
>  	u32 speed_hz = spi->max_speed_hz;
>  
> @@ -911,14 +913,15 @@ static int omap2_mcspi_setup_transfer(struct spi_device *spi,
>  	if (t && t->speed_hz)
>  		speed_hz = t->speed_hz;
>  
> -	speed_hz = min_t(u32, speed_hz, OMAP2_MCSPI_MAX_FREQ);
> -	if (speed_hz < (OMAP2_MCSPI_MAX_FREQ / OMAP2_MCSPI_MAX_DIVIDER)) {
> -		clkd = omap2_mcspi_calc_divisor(speed_hz);
> -		speed_hz = OMAP2_MCSPI_MAX_FREQ >> clkd;
> +	ref_clk_hz = mcspi->ref_clk_hz;
> +	speed_hz = min_t(u32, speed_hz, ref_clk_hz);
> +	if (speed_hz < (ref_clk_hz / OMAP2_MCSPI_MAX_DIVIDER)) {
> +		clkd = omap2_mcspi_calc_divisor(speed_hz, ref_clk_hz);
> +		speed_hz = ref_clk_hz >> clkd;
>  		clkg = 0;
>  	} else {
> -		div = (OMAP2_MCSPI_MAX_FREQ + speed_hz - 1) / speed_hz;
> -		speed_hz = OMAP2_MCSPI_MAX_FREQ / div;
> +		div = (ref_clk_hz + speed_hz - 1) / speed_hz;
> +		speed_hz = ref_clk_hz / div;
>  		clkd = (div - 1) & 0xf;
>  		extclk = (div - 1) >> 4;
>  		clkg = OMAP2_MCSPI_CHCONF_CLKG;
> @@ -1448,8 +1451,6 @@ static int omap2_mcspi_probe(struct platform_device *pdev)
>  	master->cleanup = omap2_mcspi_cleanup;
>  	master->slave_abort = omap2_mcspi_slave_abort;
>  	master->dev.of_node = node;
> -	master->max_speed_hz = OMAP2_MCSPI_MAX_FREQ;
> -	master->min_speed_hz = OMAP2_MCSPI_MAX_FREQ >> 15;
>  	master->use_gpio_descriptors = true;
>  
>  	platform_set_drvdata(pdev, master);
> @@ -1519,6 +1520,14 @@ static int omap2_mcspi_probe(struct platform_device *pdev)
>  		goto free_master;
>  	}
>  
> +	mcspi->clk = devm_clk_get_optional_enabled(&pdev->dev, NULL);
> +	if (mcspi->clk)
> +		mcspi->ref_clk_hz = clk_get_rate(mcspi->clk);
> +	else
> +		mcspi->ref_clk_hz = OMAP2_MCSPI_MAX_FREQ;
> +	master->max_speed_hz = mcspi->ref_clk_hz;
> +	master->min_speed_hz = mcspi->ref_clk_hz >> 15;
> +
>  	pm_runtime_use_autosuspend(&pdev->dev);
>  	pm_runtime_set_autosuspend_delay(&pdev->dev, SPI_AUTOSUSPEND_TIMEOUT);
>  	pm_runtime_enable(&pdev->dev);
> -- 
> 2.17.1
> 

-- 
Best regards,
Dhruva Gole <d-gole@...com>