linux-kernel - Re: [PATCH] mmc: sdhci-of-at91: add presets setup

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Message-ID: <5721CAB2.5000207@intel.com>
Date:	Thu, 28 Apr 2016 11:32:50 +0300
From:	Adrian Hunter <adrian.hunter@...el.com>
To:	Ludovic Desroches <ludovic.desroches@...el.com>,
	ulf.hansson@...aro.org
Cc:	linux-mmc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, nicolas.ferre@...el.com
Subject: Re: [PATCH] mmc: sdhci-of-at91: add presets setup

On 21/04/16 16:54, Ludovic Desroches wrote:
> The controller claims to support SDR104. In fact, it only supports a
> degraded SDR104 since the maximum frequency of the SD clock is 120 MHz
> instead of 208 MHz.
> The sdhci core is unaware of it and will compute a wrong clock divider.
> We can deal with this specific case by using presets.
> 
> Signed-off-by: Ludovic Desroches <ludovic.desroches@...el.com>
> ---
>  drivers/mmc/host/sdhci-of-at91.c | 24 ++++++++++++++++++++++++
>  1 file changed, 24 insertions(+)
> 
> diff --git a/drivers/mmc/host/sdhci-of-at91.c b/drivers/mmc/host/sdhci-of-at91.c
> index c1923c0..76308b1 100644
> --- a/drivers/mmc/host/sdhci-of-at91.c
> +++ b/drivers/mmc/host/sdhci-of-at91.c
> @@ -18,6 +18,7 @@
>  #include <linux/delay.h>
>  #include <linux/err.h>
>  #include <linux/io.h>
> +#include <linux/kernel.h>
>  #include <linux/mmc/host.h>
>  #include <linux/mmc/slot-gpio.h>
>  #include <linux/module.h>
> @@ -163,6 +164,7 @@ static int sdhci_at91_probe(struct platform_device *pdev)
>  	unsigned int			clk_base, clk_mul;
>  	unsigned int			gck_rate, real_gck_rate;
>  	int				ret;
> +	unsigned int			preset_div, preset_common = 0x400; /* drv type B, programmable clock mode */

preset_common is a constant, so why not #define it?

>  
>  	match = of_match_device(sdhci_at91_dt_match, &pdev->dev);
>  	if (!match)
> @@ -230,6 +232,28 @@ static int sdhci_at91_probe(struct platform_device *pdev)
>  			 clk_mul, real_gck_rate);
>  	}
>  
> +	/*
> +	 * We have to set preset values because it depends on the clk_mul
> +	 * value. Moreover, SDR104 is supported in a degraded mode since the
> +	 * maximum sd clock value is 120 MHz instead of 208 MHz. For that
> +	 * reason, we need to use presets to support SDR104.
> +	 */
> +	preset_div = DIV_ROUND_UP(real_gck_rate, 24000000) - 1;
> +	writew(preset_common | preset_div,
> +	       host->ioaddr + SDHCI_PRESET_FOR_SDR12);
> +	preset_div = DIV_ROUND_UP(real_gck_rate, 50000000) - 1;
> +	writew(preset_common | preset_div,
> +	       host->ioaddr + SDHCI_PRESET_FOR_SDR25);
> +	preset_div = DIV_ROUND_UP(real_gck_rate, 100000000) - 1;
> +	writew(preset_common | preset_div,
> +	       host->ioaddr + SDHCI_PRESET_FOR_SDR50);
> +	preset_div = DIV_ROUND_UP(real_gck_rate, 120000000) - 1;
> +	writew(preset_common | preset_div,
> +	       host->ioaddr + SDHCI_PRESET_FOR_SDR104);
> +	preset_div = DIV_ROUND_UP(real_gck_rate, 50000000) - 1;
> +	writew(preset_common | preset_div,
> +	       host->ioaddr + SDHCI_PRESET_FOR_DDR50);
> +
>  	clk_prepare_enable(priv->mainck);
>  	clk_prepare_enable(priv->gck);
>  
>