linux-kernel - Re: [PATCH 3/4] phy: rockchip-emmc: configure default output tap delay

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Date:	Mon, 20 Jun 2016 18:41:52 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	Brian Norris <briannorris@...omium.org>
CC:	Heiko Stuebner <heiko@...ech.de>, <linux-kernel@...r.kernel.org>,
	<linux-rockchip@...ts.infradead.org>,
	Doug Anderson <dianders@...omium.org>,
	Shawn Lin <shawn.lin@...k-chips.com>,
	<linux-arm-kernel@...ts.infradead.org>,
	Brian Norris <computersforpeace@...il.com>
Subject: Re: [PATCH 3/4] phy: rockchip-emmc: configure default output tap
 delay



On Friday 13 May 2016 04:13 AM, Brian Norris wrote:
> The output tap delay controls helps maintain the hold requirements for
> eMMC. The exact value is dependent on the SoC and other factors, though
> it isn't really an exact science. But the default of 0 is not very good,
> as it doesn't give the eMMC much hold time, so let's bump up to 4
> (approx 90 degree phase?). If we need to configure this any further
> (e.g., based on board or speed factors), we may need to consider a
> device tree representation.
> 
> Suggested-by: Shawn Lin <shawn.lin@...k-chips.com>
> Signed-off-by: Brian Norris <briannorris@...omium.org>

Acked-by: Kishon Vijay Abraham I <kishon@...com>
> ---
>  drivers/phy/phy-rockchip-emmc.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/drivers/phy/phy-rockchip-emmc.c b/drivers/phy/phy-rockchip-emmc.c
> index 5641dede32f6..f94d3a6587ed 100644
> --- a/drivers/phy/phy-rockchip-emmc.c
> +++ b/drivers/phy/phy-rockchip-emmc.c
> @@ -69,6 +69,11 @@
>  #define PHYCTRL_DR_66OHM	0x2
>  #define PHYCTRL_DR_100OHM	0x3
>  #define PHYCTRL_DR_40OHM	0x4
> +#define PHYCTRL_OTAPDLYENA		0x1
> +#define PHYCTRL_OTAPDLYENA_MASK		0x1
> +#define PHYCTRL_OTAPDLYENA_SHIFT	0xb
> +#define PHYCTRL_OTAPDLYSEL_MASK		0xf
> +#define PHYCTRL_OTAPDLYSEL_SHIFT	0x7
>  
>  struct rockchip_emmc_phy {
>  	unsigned int	reg_offset;
> @@ -181,6 +186,20 @@ static int rockchip_emmc_phy_power_on(struct phy *phy)
>  				   PHYCTRL_DR_MASK,
>  				   PHYCTRL_DR_SHIFT));
>  
> +	/* Output tap delay: enable */
> +	regmap_write(rk_phy->reg_base,
> +		     rk_phy->reg_offset + GRF_EMMCPHY_CON0,
> +		     HIWORD_UPDATE(PHYCTRL_OTAPDLYENA,
> +				   PHYCTRL_OTAPDLYENA_MASK,
> +				   PHYCTRL_OTAPDLYENA_SHIFT));
> +
> +	/* Output tap delay */
> +	regmap_write(rk_phy->reg_base,
> +		     rk_phy->reg_offset + GRF_EMMCPHY_CON0,
> +		     HIWORD_UPDATE(4,
> +				   PHYCTRL_OTAPDLYSEL_MASK,
> +				   PHYCTRL_OTAPDLYSEL_SHIFT));
> +
>  	/* Power up emmc phy analog blocks */
>  	ret = rockchip_emmc_phy_power(rk_phy, PHYCTRL_PDB_PWR_ON);
>  	if (ret)
>