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

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Date:	Thu, 28 Apr 2016 14:23:19 +0200
From:	Ludovic Desroches <ludovic.desroches@...el.com>
To:	Adrian Hunter <adrian.hunter@...el.com>
CC:	Ludovic Desroches <ludovic.desroches@...el.com>,
	<ulf.hansson@...aro.org>, <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 Thu, Apr 28, 2016 at 11:32:50AM +0300, Adrian Hunter wrote:
> 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?

No reason, a mistake, I'll fix 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);
> >  
> > 
>