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Subject: Re: [PATCH 1/3] phy: rockchip-emmc: Allow to set drive impedance via
 DTS.
From:   =?utf-8?Q?Christoph_M=C3=BCllner?= 
        <christoph.muellner@theobroma-systems.com>
In-Reply-To: <1347b956-5682-1f86-b38c-7768bb9ffd23@arm.com>
Date:   Fri, 1 Mar 2019 18:38:07 +0100
Cc:     robh+dt@kernel.org, mark.rutland@arm.com, heiko@sntech.de,
        shawn.lin@rock-chips.com, devicetree@vger.kernel.org,
        Matthias Brugger <mbrugger@suse.com>,
        linux-kernel@vger.kernel.org,
        Emil Renner Berthing <kernel@esmil.dk>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        Randy Li <ayaka@soulik.info>,
        Douglas Anderson <dianders@chromium.org>,
        Vicente Bergas <vicencb@gmail.com>,
        Kishon Vijay Abraham I <kishon@ti.com>,
        linux-rockchip@lists.infradead.org,
        Tony Xie <tony.xie@rock-chips.com>,
        Klaus Goger <klaus.goger@theobroma-systems.com>,
        Enric Balletbo i Serra <enric.balletbo@collabora.com>,
        Philipp Tomsich <philipp.tomsich@theobroma-systems.com>,
        Ezequiel Garcia <ezequiel@collabora.com>,
        linux-arm-kernel@lists.infradead.org
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Message-Id: <0DE1481B-7F61-4D85-9593-07E9680AC0EC@theobroma-systems.com>
References: <20190301153348.29870-1-christoph.muellner@theobroma-systems.com>
 <1347b956-5682-1f86-b38c-7768bb9ffd23@arm.com>
To:     Robin Murphy <robin.murphy@arm.com>
Sender: linux-kernel-owner@vger.kernel.org
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Hi Robin,

> On 01.03.2019, at 17:51, Robin Murphy <robin.murphy@arm.com> wrote:
> 
> On 01/03/2019 15:33, Christoph Muellner wrote:
>> The rockchip-emmc PHY can be configured with different
>> drive impedance values. Currenlty a value of 50 Ohm is
>> hard coded into the driver.
>> This patch introduces the DTS property 'drive-impedance-ohm'
>> for the rockchip-emmc phy node, which uses the value from the DTS
>> to setup the drive impedance accordingly.
>> Signed-off-by: Christoph Muellner <christoph.muellner@theobroma-systems.com>
>> Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
>> ---
>>  drivers/phy/rockchip/phy-rockchip-emmc.c | 38 ++++++++++++++++++++++++++++++--
>>  1 file changed, 36 insertions(+), 2 deletions(-)
>> diff --git a/drivers/phy/rockchip/phy-rockchip-emmc.c b/drivers/phy/rockchip/phy-rockchip-emmc.c
>> index 19bf84f0bc67..5413fa73dd45 100644
>> --- a/drivers/phy/rockchip/phy-rockchip-emmc.c
>> +++ b/drivers/phy/rockchip/phy-rockchip-emmc.c
>> @@ -87,6 +87,7 @@ struct rockchip_emmc_phy {
>>  	unsigned int	reg_offset;
>>  	struct regmap	*reg_base;
>>  	struct clk	*emmcclk;
>> +	unsigned int drive_impedance;
>>  };
>>    static int rockchip_emmc_phy_power(struct phy *phy, bool on_off)
>> @@ -281,10 +282,10 @@ static int rockchip_emmc_phy_power_on(struct phy *phy)
>>  {
>>  	struct rockchip_emmc_phy *rk_phy = phy_get_drvdata(phy);
>>  -	/* Drive impedance: 50 Ohm */
>> +	/* Drive impedance: from DTS */
>>  	regmap_write(rk_phy->reg_base,
>>  		     rk_phy->reg_offset + GRF_EMMCPHY_CON6,
>> -		     HIWORD_UPDATE(PHYCTRL_DR_50OHM,
>> +		     HIWORD_UPDATE(rk_phy->drive_impedance,
>>  				   PHYCTRL_DR_MASK,
>>  				   PHYCTRL_DR_SHIFT));
>>  @@ -314,6 +315,28 @@ static const struct phy_ops ops = {
>>  	.owner		= THIS_MODULE,
>>  };
>>  +static u32 convert_drive_impedance_ohm(struct platform_device *pdev, u32 dr_ohm)
>> +{
>> +	switch (dr_ohm) {
>> +	case 100:
>> +		return PHYCTRL_DR_100OHM;
>> +	case 66:
>> +		return PHYCTRL_DR_66OHM;
>> +	case 50:
>> +		return PHYCTRL_DR_50OHM;
>> +	case 40:
>> +		return PHYCTRL_DR_40OHM;
>> +	case 33:
>> +		return PHYCTRL_DR_33OHM;
>> +	}
>> +
>> +	dev_warn(&pdev->dev,
>> +		"Invalid value %u for drive-impedance-ohm. "
>> +		"Falling back to 50 Ohm.\n",
>> +		dr_ohm);
>> +	return PHYCTRL_DR_50OHM;
>> +}
>> +
>>  static int rockchip_emmc_phy_probe(struct platform_device *pdev)
>>  {
>>  	struct device *dev = &pdev->dev;
>> @@ -322,6 +345,7 @@ static int rockchip_emmc_phy_probe(struct platform_device *pdev)
>>  	struct phy_provider *phy_provider;
>>  	struct regmap *grf;
>>  	unsigned int reg_offset;
>> +	u32 val;
>>    	if (!dev->parent || !dev->parent->of_node)
>>  		return -ENODEV;
>> @@ -345,6 +369,16 @@ static int rockchip_emmc_phy_probe(struct platform_device *pdev)
>>  	rk_phy->reg_offset = reg_offset;
>>  	rk_phy->reg_base = grf;
>>  +	if (of_property_read_u32(dev->of_node, "drive-impedance-ohm", &val)) {
>> +		dev_info(dev,
>> +			"Missing drive-impedance-ohm property in node %s "
>> +			"Falling back to 50 Ohm.\n",
>> +			dev->of_node->name);
> 
> I think we're aiming to use %pOF for node names now, but here it looks redundant anyway - dev_info() will already show the device name, which for an of_platform device is the same thing.
> 
>> +		rk_phy->drive_impedance = PHYCTRL_DR_50OHM;
>> +	} else {
>> +		rk_phy->drive_impedance = convert_drive_impedance_ohm(pdev, val);
>> +	}
> 
> FWIW, if you initialise val to the default (i.e. 50) then you could get rid of the "else" case and just do the conversion unconditionally. That's a fairly common idiom for reading optional properties.

Ack. For v2 I've removed the else case (not defined value).

Thanks,
Christoph

> 
> Robin.
> 
>> +
>>  	generic_phy = devm_phy_create(dev, dev->of_node, &ops);
>>  	if (IS_ERR(generic_phy)) {
>>  		dev_err(dev, "failed to create PHY\n");