Date:   Fri, 27 Aug 2021 00:19:25 +0530
From:   Pratyush Yadav <p.yadav@...com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>
CC:     Vinod Koul <vkoul@...nel.org>,
        Paul Kocialkowski <paul.kocialkowski@...tlin.com>,
        Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        Vignesh Raghavendra <vigneshr@...com>,
        Nikhil Devshatwar <nikhil.nd@...com>,
        Chunfeng Yun <chunfeng.yun@...iatek.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Peter Chen <peter.chen@....com>,
        <linux-kernel@...r.kernel.org>, <linux-phy@...ts.infradead.org>
Subject: Re: [PATCH v4 2/6] phy: cdns-dphy: Add Rx support

Hi Laurent,

Thanks for reviewing.

On 23/08/21 04:37AM, Laurent Pinchart wrote:
> Hi Pratyush,
> 
> Thank you for the patch.
> 
> On Sat, Aug 21, 2021 at 12:33:42AM +0530, Pratyush Yadav wrote:
> > The Cadence DPHY can be used to receive image data over the CSI-2
> > protocol. Add support for Rx mode. The programming sequence differs from
> > the Tx mode so it is added as a separate set of hooks to isolate the two
> > paths. The mode in which the DPHY has to be used is selected based on
> > the compatible.
> > 
> > Signed-off-by: Pratyush Yadav <p.yadav@...com>
> > 
> > ---
> > 
> > Changes in v4:
> > - Drop the submode parts. Use a different compatible for the Rx ops.
> > - Make bands and num_bands static.
> > 
> > Changes in v3:
> > - Use a table to select the band.
> > - Use a table to poll the data lane ready bits.
> > - Multiply the DPHY HS clock rate by 2 to get the bit rate since the
> >   clock is DDR.
> > 
> >  drivers/phy/cadence/cdns-dphy.c | 171 ++++++++++++++++++++++++++++++++
> >  1 file changed, 171 insertions(+)
> > 
> > diff --git a/drivers/phy/cadence/cdns-dphy.c b/drivers/phy/cadence/cdns-dphy.c
> > index 0a169d649216..149fccdfad38 100644
> > --- a/drivers/phy/cadence/cdns-dphy.c
> > +++ b/drivers/phy/cadence/cdns-dphy.c
> > @@ -1,11 +1,14 @@
> >  // SPDX-License-Identifier: GPL-2.0+
> >  /*
> >   * Copyright: 2017-2018 Cadence Design Systems, Inc.
> > + * Copyright (C) 2021 Texas Instruments Incorporated - https://www.ti.com/
> >   */
> >  
> >  #include <linux/bitops.h>
> > +#include <linux/bitfield.h>
> 
> Alphabetical order please.
> 
> >  #include <linux/clk.h>
> >  #include <linux/io.h>
> > +#include <linux/iopoll.h>
> >  #include <linux/module.h>
> >  #include <linux/of_address.h>
> >  #include <linux/of_device.h>
> > @@ -25,10 +28,14 @@
> >  #define DPHY_PMA_RCLK(reg)		(0x600 + (reg))
> >  #define DPHY_PMA_RDATA(lane, reg)	(0x700 + ((lane) * 0x100) + (reg))
> >  #define DPHY_PCS(reg)			(0xb00 + (reg))
> > +#define DPHY_ISO(reg)			(0xc00 + (reg))
> >  
> >  #define DPHY_CMN_SSM			DPHY_PMA_CMN(0x20)
> >  #define DPHY_CMN_SSM_EN			BIT(0)
> > +#define DPHY_CMN_RX_BANDGAP_TIMER_MASK	GENMASK(8, 1)
> >  #define DPHY_CMN_TX_MODE_EN		BIT(9)
> > +#define DPHY_CMN_RX_MODE_EN		BIT(10)
> > +#define DPHY_CMN_RX_BANDGAP_TIMER	0x14
> >  
> >  #define DPHY_CMN_PWM			DPHY_PMA_CMN(0x40)
> >  #define DPHY_CMN_PWM_DIV(x)		((x) << 20)
> > @@ -45,10 +52,27 @@
> >  #define DPHY_CMN_OPDIV_FROM_REG		BIT(6)
> >  #define DPHY_CMN_OPDIV(x)		((x) << 7)
> >  
> > +#define DPHY_BAND_CFG			DPHY_PCS(0x0)
> > +#define DPHY_BAND_CFG_LEFT_BAND		GENMASK(4, 0)
> > +#define DPHY_BAND_CFG_RIGHT_BAND	GENMASK(9, 5)
> > +
> >  #define DPHY_PSM_CFG			DPHY_PCS(0x4)
> >  #define DPHY_PSM_CFG_FROM_REG		BIT(0)
> >  #define DPHY_PSM_CLK_DIV(x)		((x) << 1)
> >  
> > +#define DPHY_POWER_ISLAND_EN_DATA	DPHY_PCS(0x8)
> > +#define DPHY_POWER_ISLAND_EN_DATA_VAL	0xaaaaaaaa
> > +#define DPHY_POWER_ISLAND_EN_CLK	DPHY_PCS(0xc)
> > +#define DPHY_POWER_ISLAND_EN_CLK_VAL	0xaa
> > +
> > +#define DPHY_ISO_CL_CTRL_L		DPHY_ISO(0x10)
> > +#define DPHY_ISO_DL_CTRL_L0		DPHY_ISO(0x14)
> > +#define DPHY_ISO_DL_CTRL_L1		DPHY_ISO(0x20)
> > +#define DPHY_ISO_DL_CTRL_L2		DPHY_ISO(0x30)
> > +#define DPHY_ISO_DL_CTRL_L3		DPHY_ISO(0x3c)
> > +#define DPHY_ISO_LANE_READY_BIT		0
> > +#define DPHY_ISO_LANE_READY_TIMEOUT_MS	100UL
> > +
> >  #define DSI_HBP_FRAME_OVERHEAD		12
> >  #define DSI_HSA_FRAME_OVERHEAD		14
> >  #define DSI_HFP_FRAME_OVERHEAD		6
> > @@ -57,6 +81,9 @@
> >  #define DSI_NULL_FRAME_OVERHEAD		6
> >  #define DSI_EOT_PKT_SIZE		4
> >  
> > +#define DPHY_LANES_MIN			1
> > +#define DPHY_LANES_MAX			4
> > +
> >  struct cdns_dphy_cfg {
> >  	u8 pll_ipdiv;
> >  	u8 pll_opdiv;
> > @@ -98,6 +125,22 @@ struct cdns_dphy {
> >  	struct phy *phy;
> >  };
> >  
> > +struct cdns_dphy_rx_band {
> > +	unsigned int min_rate;
> > +	unsigned int max_rate;
> > +};
> > +
> > +/* Order of bands is important since the index is the band number. */
> > +static struct cdns_dphy_rx_band bands[] = {
> 
> static const
> 
> > +	{80, 100}, {100, 120}, {120, 160}, {160, 200}, {200, 240},
> > +	{240, 280}, {280, 320}, {320, 360}, {360, 400}, {400, 480},
> > +	{480, 560}, {560, 640}, {640, 720}, {720, 800}, {800, 880},
> > +	{880, 1040}, {1040, 1200}, {1200, 1350}, {1350, 1500}, {1500, 1750},
> > +	{1750, 2000}, {2000, 2250}, {2250, 2500}
> > +};
> > +
> > +static int num_bands = ARRAY_SIZE(bands);
> 
> No need for a variable (which should be const otherwise), you can use
> ARRAY_SIZE(bands) where needed.
> 
> > +
> >  static int cdns_dsi_get_dphy_pll_cfg(struct cdns_dphy *dphy,
> >  				     struct cdns_dphy_cfg *cfg,
> >  				     struct phy_configure_opts_mipi_dphy *opts,
> > @@ -309,6 +352,132 @@ static const struct cdns_dphy_ops tx_ref_dphy_ops = {
> >  	.set_psm_div = cdns_dphy_ref_set_psm_div,
> >  };
> >  
> > +static int cdns_dphy_rx_power_on(struct cdns_dphy *dphy)
> > +{
> > +	/* Start RX state machine. */
> > +	writel(DPHY_CMN_SSM_EN | DPHY_CMN_RX_MODE_EN |
> > +	       FIELD_PREP(DPHY_CMN_RX_BANDGAP_TIMER_MASK,
> > +			  DPHY_CMN_RX_BANDGAP_TIMER),
> > +	       dphy->regs + DPHY_CMN_SSM);
> > +
> > +	return 0;
> > +}
> > +
> > +static int cdns_dphy_rx_power_off(struct cdns_dphy *dphy)
> > +{
> > +	writel(0, dphy->regs + DPHY_CMN_SSM);
> > +
> > +	return 0;
> > +}
> > +
> > +static int cdns_dphy_rx_get_band_ctrl(unsigned long hs_clk_rate)
> > +{
> > +	unsigned int rate;
> > +	int i;
> 
> i is never negative, you can make it an unsigned int.
> 
> > +
> > +	rate = hs_clk_rate / 1000000UL;
> > +	/* Since CSI-2 clock is DDR, the bit rate is twice the clock rate. */
> > +	rate *= 2;
> > +
> > +	if (rate < bands[0].min_rate || rate >= bands[num_bands - 1].max_rate)
> > +		return -EOPNOTSUPP;
> > +
> > +	for (i = 0; i < num_bands; i++) {
> > +		if (rate >= bands[i].min_rate && rate < bands[i].max_rate)
> 
> You can replace this with
> 
> 		if (rate < bands[i].max_rate)
> 
> as the bands are in increasing order.
> 
> > +			return i;
> > +	}
> > +
> > +	/* Unreachable. */
> > +	WARN(1, "Reached unreachable code.");
> > +	return -EINVAL;
> 
> That's not very nice.
> 
> As a clock rate higher than the maximum isn't supposed to happen, you
> could drop that initial check (it won't affect performance) and return
> -EOPNOTSUPP here without a WARN().

Ok.

> 
> > +}
> > +
> > +static int cdns_dphy_rx_wait_for_bit(void __iomem *addr, unsigned int bit)
> > +{
> > +	u32 val;
> > +
> > +	return readl_relaxed_poll_timeout(addr, val, val & BIT(bit), 10,
> > +					  DPHY_ISO_LANE_READY_TIMEOUT_MS * 1000);
> 
> A busy wait for one second is quite long. How long does it typically
> take for the condition to be true ?

I have not measured. I don't see any timing information in the 
datasheet.

But the timeout is 100 miliseconds not 1 second. 
readl_relaxed_poll_timeout() expects microseconds, so we multiply by 
1000. The value of DPHY_ISO_LANE_READY_TIMEOUT_MS is 100, so it will be 
a 100 ms timeout, which I think is reasonable.

> 
> > +}
> > +
> > +static int cdns_dphy_rx_wait_lane_ready(struct cdns_dphy *dphy, int lanes)
> 
> lanes should be an unsigned int.
> 
> > +{
> > +	void __iomem *reg = dphy->regs;
> 
> You can use dphy->regs directly in the code below.
> 
> > +	u32 data_lane_ctrl[] = {DPHY_ISO_DL_CTRL_L0, DPHY_ISO_DL_CTRL_L1,
> > +				DPHY_ISO_DL_CTRL_L2, DPHY_ISO_DL_CTRL_L3};
> 
> static const, and move it first in the function.

Ok. But out of curiosity, why?

> 
> > +	int ret, i;
> 
> i is never negative here either.

Yes. Will change to unsigned.

> 
> > +
> > +	/* Data lanes. Minimum one lane is mandatory. */
> > +	if (lanes < DPHY_LANES_MIN || lanes > DPHY_LANES_MAX)
> > +		return -EINVAL;
> > +
> > +	/* Clock lane */
> > +	ret = cdns_dphy_rx_wait_for_bit(reg + DPHY_ISO_CL_CTRL_L,
> > +					DPHY_ISO_LANE_READY_BIT);
> > +	if (ret)
> > +		return ret;
> > +
> > +	for (i = 0; i < lanes; i++) {
> > +		ret = cdns_dphy_rx_wait_for_bit(reg + data_lane_ctrl[i],
> > +						DPHY_ISO_LANE_READY_BIT);
> > +		if (ret)
> > +			return ret;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int cdns_dphy_rx_configure(struct cdns_dphy *dphy,
> > +				  union phy_configure_opts *opts)
> > +{
> > +	unsigned int reg;
> > +	int band_ctrl, ret;
> > +
> > +	band_ctrl = cdns_dphy_rx_get_band_ctrl(opts->mipi_dphy.hs_clk_rate);
> > +	if (band_ctrl < 0)
> > +		return band_ctrl;
> > +
> > +	reg = FIELD_PREP(DPHY_BAND_CFG_LEFT_BAND, band_ctrl) |
> > +	      FIELD_PREP(DPHY_BAND_CFG_RIGHT_BAND, band_ctrl);
> > +	writel(reg, dphy->regs + DPHY_BAND_CFG);
> > +
> > +	/*
> > +	 * Set the required power island phase 2 time. This is mandated by DPHY
> > +	 * specs.
> > +	 */
> > +	reg = DPHY_POWER_ISLAND_EN_DATA_VAL;
> > +	writel(reg, dphy->regs + DPHY_POWER_ISLAND_EN_DATA);
> > +	reg = DPHY_POWER_ISLAND_EN_CLK_VAL;
> > +	writel(reg, dphy->regs + DPHY_POWER_ISLAND_EN_CLK);
> > +
> > +	ret = cdns_dphy_rx_wait_lane_ready(dphy, opts->mipi_dphy.lanes);
> > +	if (ret) {
> > +		dev_err(dphy->dev, "DPHY wait for lane ready timeout\n");
> > +		return ret;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static int cdns_dphy_rx_validate(struct cdns_dphy *dphy, enum phy_mode mode,
> > +				 int submode, union phy_configure_opts *opts)
> > +{
> > +	int ret;
> > +
> > +	ret = cdns_dphy_rx_get_band_ctrl(opts->mipi_dphy.hs_clk_rate);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	return phy_mipi_dphy_config_validate(&opts->mipi_dphy);
> > +}
> > +
> > +static const struct cdns_dphy_ops rx_ref_dphy_ops = {
> > +	.power_on = cdns_dphy_rx_power_on,
> > +	.power_off = cdns_dphy_rx_power_off,
> > +	.configure = cdns_dphy_rx_configure,
> > +	.validate = cdns_dphy_rx_validate,
> > +};
> > +
> >  static int cdns_dphy_validate(struct phy *phy, enum phy_mode mode, int submode,
> >  			      union phy_configure_opts *opts)
> >  {
> > @@ -421,6 +590,7 @@ static int cdns_dphy_remove(struct platform_device *pdev)
> >  
> >  static const struct of_device_id cdns_dphy_of_match[] = {
> >  	{ .compatible = "cdns,dphy", .data = &tx_ref_dphy_ops },
> > +	{ .compatible = "cdns,dphy-rx", .data = &rx_ref_dphy_ops },
> >  	{ /* sentinel */ },
> >  };
> >  MODULE_DEVICE_TABLE(of, cdns_dphy_of_match);
> > @@ -436,5 +606,6 @@ static struct platform_driver cdns_dphy_platform_driver = {
> >  module_platform_driver(cdns_dphy_platform_driver);
> >  
> >  MODULE_AUTHOR("Maxime Ripard <maxime.ripard@...tlin.com>");
> > +MODULE_AUTHOR("Pratyush Yadav <p.yadav@...com>");
> >  MODULE_DESCRIPTION("Cadence MIPI D-PHY Driver");
> >  MODULE_LICENSE("GPL");
> 
> -- 
> Regards,
> 
> Laurent Pinchart

-- 
Regards,
Pratyush Yadav
Texas Instruments Inc.

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