linux-kernel - Re: [PATCH 1/2] soundwire: cadence_master: set frame shape and divider based on actual clk freq

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Message-ID: <ff37ea9b-e162-4d6f-ae33-26ec2e342cc6@linux.dev>
Date: Tue, 7 Jan 2025 13:19:54 -0600
From: Pierre-Louis Bossart <pierre-louis.bossart@...ux.dev>
To: Bard Liao <yung-chuan.liao@...ux.intel.com>, linux-sound@...r.kernel.org,
 vkoul@...nel.org
Cc: vinod.koul@...aro.org, linux-kernel@...r.kernel.org, bard.liao@...el.com
Subject: Re: [PATCH 1/2] soundwire: cadence_master: set frame shape and
 divider based on actual clk freq


> -static void cdns_init_clock_ctrl(struct sdw_cdns *cdns)
> +static int cdns_init_clock_ctrl(struct sdw_cdns *cdns)
>  {
>  	struct sdw_bus *bus = &cdns->bus;
>  	struct sdw_master_prop *prop = &bus->prop;
>  	u32 val;
>  	u32 ssp_interval;
>  	int divider;
> +	int freq;
>  
>  	dev_dbg(cdns->dev, "mclk %d max %d row %d col %d\n",
>  		prop->mclk_freq,
> @@ -1356,13 +1357,25 @@ static void cdns_init_clock_ctrl(struct sdw_cdns *cdns)
>  		prop->default_col);
>  
>  	/* Set clock divider */
> -	divider	= (prop->mclk_freq / prop->max_clk_freq) - 1;
> +	divider	= (prop->mclk_freq * SDW_DOUBLE_RATE_FACTOR /
> +		bus->params.curr_dr_freq) - 1;
> +	freq = bus->params.curr_dr_freq >> 1;

do you actually need this intermediate variable? see below [1] ...

>  
>  	cdns_updatel(cdns, CDNS_MCP_CLK_CTRL0,
>  		     CDNS_MCP_CLK_MCLKD_MASK, divider);
>  	cdns_updatel(cdns, CDNS_MCP_CLK_CTRL1,
>  		     CDNS_MCP_CLK_MCLKD_MASK, divider);
>  
> +	/* Set frame shape base on the actual bus frequency. */
> +	if (!prop->default_frame_rate || !prop->default_row) {
> +		dev_err(cdns->dev, "Default frame_rate %d or row %d is invalid\n",
> +			prop->default_frame_rate, prop->default_row);
> +		return -EINVAL;
> +	}

maybe check the values before writing the divider registers?

> +
> +	prop->default_col = freq * SDW_DOUBLE_RATE_FACTOR /
> +			    prop->default_frame_rate / prop->default_row;

[1] ... this is the only place where 'freq' is used, and you multiply it by two after dividing it by two.

couldn't this just be:

prop->default_col = bus->params.curr_dr_freq /
		    prop->default_frame_rate / prop->default_row;