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SubjectRe: [PATCH 1/3] phy: rockchip-emmc: Allow to set drive impedance via DTS.
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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");

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