Re: [PATCH] phy: qcom-qmp: add support for voltage and pre emphesis swing

[Bjorn Andersson <bjorn.andersson@linaro.org>]

On Tue 24 Aug 16:29 PDT 2021, Kuogee Hsieh wrote:

> Add voltage and pre emphesis swing tables so that voltage and
> pre emphsis swing level can be configured base on link rate.
> 

I think it would be nice if $subject, or at least the commit message
mentioned that this relates to the DisplayPort part of the QMP driver.

Also the commit message states that this allows someone/something to
configure the properties based on link rate. But it doesn't state why
this is needed.

> Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
> ---
>  drivers/phy/qualcomm/phy-qcom-qmp.c | 95 ++++++++++++++++++++++++++++++++-----
>  1 file changed, 82 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/phy/qualcomm/phy-qcom-qmp.c b/drivers/phy/qualcomm/phy-qcom-qmp.c
> index 31036aa..52bab6e 100644
> --- a/drivers/phy/qualcomm/phy-qcom-qmp.c
> +++ b/drivers/phy/qualcomm/phy-qcom-qmp.c
> @@ -1916,7 +1916,7 @@ static const struct qmp_phy_init_tbl qmp_v4_dp_tx_tbl[] = {
>  	QMP_PHY_INIT_CFG(QSERDES_V4_TX_RES_CODE_LANE_OFFSET_RX, 0x11),
>  	QMP_PHY_INIT_CFG(QSERDES_V4_TX_TX_BAND, 0x4),
>  	QMP_PHY_INIT_CFG(QSERDES_V4_TX_TX_POL_INV, 0x0a),
> -	QMP_PHY_INIT_CFG(QSERDES_V4_TX_TX_DRV_LVL, 0x2a),
> +	QMP_PHY_INIT_CFG(QSERDES_V4_TX_TX_DRV_LVL, 0x22),

Why is this initial value changed in order to make the swing and
emphasis configurable?

>  	QMP_PHY_INIT_CFG(QSERDES_V4_TX_TX_EMP_POST1_LVL, 0x20),
>  };
>  
> @@ -3727,6 +3727,81 @@ static int qcom_qmp_v3_dp_phy_calibrate(struct qmp_phy *qphy)
>  
>  	return 0;
>  }
> +/*
> + * 0x20 deducted from tables
> + *
> + * swing_value |= DP_PHY_TXn_TX_DRV_LVL_MUX_EN;
> + * pre_emphasis_value |= DP_PHY_TXn_TX_EMP_POST1_LVL_MUX_EN;

How about rewriting this as something like
  "The values in these tables are given without MUX_EN (0x20) bit set"

?

> +*/
> +static const u8 qmp_dp_v4_pre_emphasis_hbr3_hbr2[4][4] = {
> +	/* p0    p1    p2    p3 */
> +	{ 0x00, 0x0c, 0x15, 0x1b },	/* s0 */
> +	{ 0x02, 0x0e, 0x16, 0xff },	/* s1 */
> +	{ 0x02, 0x11, 0xff, 0xff },	/* s2 */
> +	{ 0x04, 0xff, 0xff, 0xff }	/* s3 */
> +};
> +
> +static const u8 qmp_dp_v4_voltage_swing_hbr3_hbr2[4][4] = {
> +	/* p0    p1    p2    p3 */
> +	{ 0x02, 0x12, 0x16, 0x1a },	/* s0 */
> +	{ 0x09, 0x19, 0x1f, 0xff },	/* s1 */
> +	{ 0x10, 0x1f, 0xff, 0xff },	/* s2 */
> +	{ 0x1f, 0xff, 0xff, 0xff }	/* s3 */
> +};
> +
> +static const u8 qmp_dp_v4_pre_emphasis_hbr_rbr[4][4] = {
> +	/* p0    p1    p2    p3 */
> +	{ 0x00, 0x0e, 0x15, 0x1b },	/* s0 */
> +	{ 0x00, 0x0e, 0x15, 0xff },	/* s1 */
> +	{ 0x00, 0x0e, 0xff, 0xff },	/* s2 */
> +	{ 0x04, 0xff, 0xff, 0xff }	/* s3 */
> +};
> +
> +static const u8 qmp_dp_v4_voltage_swing_hbr_rbr[4][4] = {
> +	/* p0    p1    p2    p3 */
> +	{ 0x08, 0x0f, 0x16, 0x1f },	/* s0 */
> +	{ 0x11, 0x1e, 0x1f, 0xff },	/* s1 */
> +	{ 0x16, 0x1f, 0xff, 0xff },	/* s2 */
> +	{ 0x1f, 0xff, 0xff, 0xff }	/* s3 */
> +};
> +
> +static int qcom_qmp_v4_phy_configure_dp_swing(struct qmp_phy *qphy,
> +		unsigned int drv_lvl_reg, unsigned int emp_post_reg)
> +{
> +	const struct phy_configure_opts_dp *dp_opts = &qphy->dp_opts;
> +	unsigned int v_level = 0, p_level = 0;
> +	u8 voltage_swing_cfg, pre_emphasis_cfg;

The "_cfg" suffix on these variables doesn't really add any value.
Frankly, calling them "voltage" (or "swing") and "emphasis" seems just
as expressive, but easier to read.

> +	int i;
> +
> +	for (i = 0; i < dp_opts->lanes; i++) {
> +		v_level = max(v_level, dp_opts->voltage[i]);
> +		p_level = max(p_level, dp_opts->pre[i]);
> +	}
> +
> +
> +	if (dp_opts->link_rate <= 2700) {
> +		voltage_swing_cfg = qmp_dp_v4_voltage_swing_hbr_rbr[v_level][p_level];
> +		pre_emphasis_cfg = qmp_dp_v4_pre_emphasis_hbr_rbr[v_level][p_level];
> +	} else {
> +		voltage_swing_cfg = qmp_dp_v4_voltage_swing_hbr3_hbr2[v_level][p_level];
> +		pre_emphasis_cfg = qmp_dp_v4_pre_emphasis_hbr3_hbr2[v_level][p_level];
> +	}
> +
> +	/* TODO: Move check to config check */
> +	if (voltage_swing_cfg == 0xFF && pre_emphasis_cfg == 0xFF)

Why is this && and not || ? 

> +		return -EINVAL;
> +
> +	/* Enable MUX to use Cursor values from these registers */
> +	voltage_swing_cfg |= DP_PHY_TXn_TX_DRV_LVL_MUX_EN;
> +	pre_emphasis_cfg |= DP_PHY_TXn_TX_EMP_POST1_LVL_MUX_EN;
> +
> +	writel(voltage_swing_cfg, qphy->tx + drv_lvl_reg);
> +	writel(pre_emphasis_cfg, qphy->tx + emp_post_reg);
> +	writel(voltage_swing_cfg, qphy->tx2 + drv_lvl_reg);
> +	writel(pre_emphasis_cfg, qphy->tx2 + emp_post_reg);
> +

This function is called once, so why is drv_lvl_reg and emp_post_reg
variables passed to the function, rather than just using the defines
directly?

Regards,
Bjorn

> +	return 0;
> +}
>  
>  static void qcom_qmp_v4_phy_dp_aux_init(struct qmp_phy *qphy)
>  {
> @@ -3757,14 +3832,7 @@ static void qcom_qmp_v4_phy_dp_aux_init(struct qmp_phy *qphy)
>  
>  static void qcom_qmp_v4_phy_configure_dp_tx(struct qmp_phy *qphy)
>  {
> -	/* Program default values before writing proper values */
> -	writel(0x27, qphy->tx + QSERDES_V4_TX_TX_DRV_LVL);
> -	writel(0x27, qphy->tx2 + QSERDES_V4_TX_TX_DRV_LVL);
> -
> -	writel(0x20, qphy->tx + QSERDES_V4_TX_TX_EMP_POST1_LVL);
> -	writel(0x20, qphy->tx2 + QSERDES_V4_TX_TX_EMP_POST1_LVL);
> -
> -	qcom_qmp_phy_configure_dp_swing(qphy,
> +	qcom_qmp_v4_phy_configure_dp_swing(qphy,
>  			QSERDES_V4_TX_TX_DRV_LVL,
>  			QSERDES_V4_TX_TX_EMP_POST1_LVL);
>  }
> @@ -3885,6 +3953,9 @@ static int qcom_qmp_v4_phy_configure_dp_phy(struct qmp_phy *qphy)
>  	writel(drvr1_en, qphy->tx2 + QSERDES_V4_TX_HIGHZ_DRVR_EN);
>  	writel(bias1_en, qphy->tx2 + QSERDES_V4_TX_TRANSCEIVER_BIAS_EN);
>  
> +	writel(0x0a, qphy->tx + QSERDES_V4_TX_TX_POL_INV);
> +	writel(0x0a, qphy->tx2 + QSERDES_V4_TX_TX_POL_INV);
> +
>  	writel(0x18, qphy->pcs + QSERDES_DP_PHY_CFG);
>  	udelay(2000);
>  	writel(0x19, qphy->pcs + QSERDES_DP_PHY_CFG);
> @@ -3896,11 +3967,9 @@ static int qcom_qmp_v4_phy_configure_dp_phy(struct qmp_phy *qphy)
>  			10000))
>  		return -ETIMEDOUT;
>  
> -	writel(0x0a, qphy->tx + QSERDES_V4_TX_TX_POL_INV);
> -	writel(0x0a, qphy->tx2 + QSERDES_V4_TX_TX_POL_INV);
>  
> -	writel(0x27, qphy->tx + QSERDES_V4_TX_TX_DRV_LVL);
> -	writel(0x27, qphy->tx2 + QSERDES_V4_TX_TX_DRV_LVL);
> +	writel(0x22, qphy->tx + QSERDES_V4_TX_TX_DRV_LVL);
> +	writel(0x22, qphy->tx2 + QSERDES_V4_TX_TX_DRV_LVL);
>  
>  	writel(0x20, qphy->tx + QSERDES_V4_TX_TX_EMP_POST1_LVL);
>  	writel(0x20, qphy->tx2 + QSERDES_V4_TX_TX_EMP_POST1_LVL);
> -- 
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>