linux-kernel - Re: [PATCH v2 3/8] mmc: sdhci-st: Add delay management functions for top registers (eMMC).

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Date:	Tue, 3 Mar 2015 11:47:56 +0100
From:	Maxime Coquelin <maxime.coquelin@...com>
To:	Peter Griffin <peter.griffin@...aro.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <patrice.chotard@...com>,
	<srinivas.kandagatla@...il.com>, <chris@...ntf.net>,
	<ulf.hansson@...aro.org>
CC:	<lee.jones@...aro.org>, <devicetree@...r.kernel.org>,
	<linux-mmc@...r.kernel.org>, <peppe.cavallaro@...com>
Subject: Re: [PATCH v2 3/8] mmc: sdhci-st: Add delay management functions
 for top registers (eMMC).


On 02/26/2015 02:10 PM, Peter Griffin wrote:
> Due to the tight timing constriants in some UHS modes, it is required to have
s/constriant/constraints/
> some delay management in the design. Two types of delay management are supported
> in the HW: -
>
> 1) Static delay management
> 2) Dynamic delay management
>
> NB: The delay management is only there when eMMC interface is selected.
>
> 1: Static delay management: is used to provide PVT dependent static delay on the
> clock/data lines to manage setup/hold requirements of the interface. The maximum
> delay possible is 3.25ns. These delays are PVT dependent, and thus delay values
> applied are not accurate and vary across provcess voltage and temperature range.
> Due to this these delays must not be used on the very time critical paths.
>
> 2. Dynamic delay locked loop (DLL): is used to provide dynamic delay management.
> The advantage of DLL is that it provides accurate & PVT indepedent delay.
>
> The DLL is used to provide delay on the loopback clock on "Read Path" to capture
> read data reliably. On TX path the clock on which output data is transmitted is
> delayed, resulting in delay of TX data.
>
> Signed-off-by: Peter Griffin <peter.griffin@...aro.org>
> Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@...com>
> ---
>   drivers/mmc/host/sdhci-st.c | 58 +++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 58 insertions(+)
>
> diff --git a/drivers/mmc/host/sdhci-st.c b/drivers/mmc/host/sdhci-st.c
> index 0101ae9..3443cc0 100644
> --- a/drivers/mmc/host/sdhci-st.c
> +++ b/drivers/mmc/host/sdhci-st.c
> @@ -122,6 +122,64 @@ struct st_mmc_platform_data {
>   		 ST_TOP_MMC_DLY_CTRL_ATUNE_NOT_CFG_DLY | \
>   		 ST_TOP_MMC_START_DLL_LOCK)
>   
> +/*
> + * For clock speeds greater than 90MHz, we need to check that the
> + * DLL procedure has finished before switching to ultra-speed modes.
> + */
> +#define	CLK_TO_CHECK_DLL_LOCK	90000000
> +
> +static inline void st_mmcss_set_static_delay(void __iomem *ioaddr)
> +{
> +	if (ioaddr) {
Maybe you could do:
     if (!ioaddr)
         return;

     writel_relaxed....
> +		writel_relaxed(0x0, ioaddr + ST_TOP_MMC_DLY_CTRL);
> +		writel_relaxed(ST_TOP_MMC_DLY_MAX,
> +				ioaddr + ST_TOP_MMC_TX_CLK_DLY);
> +	}
> +}
> +
> +static inline void st_mmcss_set_dll(void __iomem *ioaddr)
> +{
> +	if (ioaddr) {
Ditto


> +		writel_relaxed(ST_TOP_MMC_DYN_DLY_CONF,
> +			ioaddr + ST_TOP_MMC_DLY_CTRL);
> +		writel_relaxed(ST_TOP_MMC_TX_DLL_STEP_DLY_VALID,
> +			ioaddr + ST_TOP_MMC_TX_DLL_STEP_DLY);
> +	}
> +}
> +
> +static int st_mmcss_lock_dll(void __iomem *ioaddr)
> +{
> +	unsigned long curr, value;
> +	unsigned long finish = jiffies + HZ;
> +
> +	/* Checks if the DLL procedure is finished */
> +	do {
> +		curr = jiffies;
> +		value = readl(ioaddr + ST_MMC_STATUS_R);
> +		if (value & 0x1)
> +			return 0;
> +
> +		cpu_relax();
> +	} while (!time_after_eq(curr, finish));
> +
> +	return -EBUSY;
> +}
> +
> +static int sdhci_st_set_dll_for_clock(struct sdhci_host *host)
> +{
> +	int ret = 0;
> +	struct sdhci_pltfm_host *pltfm_host = sdhci_priv(host);
> +	struct st_mmc_platform_data *pdata = pltfm_host->priv;
> +
> +	if (host->clock > CLK_TO_CHECK_DLL_LOCK) {
> +		st_mmcss_set_dll(pdata->top_ioaddr);
> +		ret = st_mmcss_lock_dll(host->ioaddr);
> +	}
> +
> +	return ret;
> +}
> +
> +
>   static u32 sdhci_st_readl(struct sdhci_host *host, int reg)
>   {
>   	u32 ret;

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