Re: [PATCH v3] drm/bridge/sii902x: Fix EDID readback

[Boris Brezillon <boris.brezillon@bootlin.com>]

On Tue,  6 Nov 2018 11:52:36 +0000
Fabrizio Castro <fabrizio.castro@bp.renesas.com> wrote:

> While adding SiI9022A support to the iwg23s board, it came
> up that when the HDMI transmitter is in pass through mode the
> device is not compliant with the I2C specification anymore,
> as it requires a far bigger tbuf, due to a delay the HDMI
> transmitter is adding when relaying the STOP condition on the
> monitor i2c side of things.
> 
> When not providing an appropriate delay after the STOP condition
> the i2c bus would get stuck. Also, any other traffic on the bus
> while talking to the monitor may cause the transaction to fail
> or even cause issues with the i2c bus as well.
> 
> I2c-gates seemed to reach consent as a possible way to address
> these issues, and as such this patch is implementing a solution
> based on that. Since others are clearly relying on the current
> implementation of the driver, this patch won't require any DT
> changes.
> 
> Since we don't want any interference during the DDC Bus
> Request/Grant procedure and while talking to the monitor, we
> have to use the adapter locking primitives rather than the
> i2c-mux locking primitives.
> 
> Signed-off-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>

Acked-by: Boris Brezillon <boris.brezillon@bootlin.com>

> 
> ---
> v2->v3:
> * Incorporated comments from Boris Brezillon and Peter Rosin
> 
> v1->v2:
> * Incorporated comments from Peter Rosin
> 
>  drivers/gpu/drm/bridge/sii902x.c | 247 ++++++++++++++++++++++++++++-----------
>  1 file changed, 178 insertions(+), 69 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/sii902x.c b/drivers/gpu/drm/bridge/sii902x.c
> index e59a135..bfa9020 100644
> --- a/drivers/gpu/drm/bridge/sii902x.c
> +++ b/drivers/gpu/drm/bridge/sii902x.c
> @@ -1,4 +1,6 @@
>  /*
> + * Copyright (C) 2018 Renesas Electronics
> + *
>   * Copyright (C) 2016 Atmel
>   *		      Bo Shen <voice.shen@atmel.com>
>   *
> @@ -21,6 +23,7 @@
>   */
>  
>  #include <linux/gpio/consumer.h>
> +#include <linux/i2c-mux.h>
>  #include <linux/i2c.h>
>  #include <linux/module.h>
>  #include <linux/regmap.h>
> @@ -86,8 +89,49 @@ struct sii902x {
>  	struct drm_bridge bridge;
>  	struct drm_connector connector;
>  	struct gpio_desc *reset_gpio;
> +	struct i2c_mux_core *i2cmux;
>  };
>  
> +static int sii902x_read_unlocked(struct i2c_client *i2c, u8 reg, u8 *val)
> +{
> +	union i2c_smbus_data data;
> +	int ret;
> +
> +	ret = __i2c_smbus_xfer(i2c->adapter, i2c->addr, i2c->flags,
> +			       I2C_SMBUS_READ, reg, I2C_SMBUS_BYTE_DATA, &data);
> +
> +	if (ret < 0)
> +		return ret;
> +
> +	*val = data.byte;
> +	return 0;
> +}
> +
> +static int sii902x_write_unlocked(struct i2c_client *i2c, u8 reg, u8 val)
> +{
> +	union i2c_smbus_data data;
> +
> +	data.byte = val;
> +
> +	return __i2c_smbus_xfer(i2c->adapter, i2c->addr, i2c->flags,
> +				I2C_SMBUS_WRITE, reg, I2C_SMBUS_BYTE_DATA,
> +				&data);
> +}
> +
> +static int sii902x_update_bits_unlocked(struct i2c_client *i2c, u8 reg, u8 mask,
> +					u8 val)
> +{
> +	int ret;
> +	u8 status;
> +
> +	ret = sii902x_read_unlocked(i2c, reg, &status);
> +	if (ret)
> +		return ret;
> +	status &= ~mask;
> +	status |= val & mask;
> +	return sii902x_write_unlocked(i2c, reg, status);
> +}
> +
>  static inline struct sii902x *bridge_to_sii902x(struct drm_bridge *bridge)
>  {
>  	return container_of(bridge, struct sii902x, bridge);
> @@ -135,41 +179,11 @@ static const struct drm_connector_funcs sii902x_connector_funcs = {
>  static int sii902x_get_modes(struct drm_connector *connector)
>  {
>  	struct sii902x *sii902x = connector_to_sii902x(connector);
> -	struct regmap *regmap = sii902x->regmap;
>  	u32 bus_format = MEDIA_BUS_FMT_RGB888_1X24;
> -	struct device *dev = &sii902x->i2c->dev;
> -	unsigned long timeout;
> -	unsigned int retries;
> -	unsigned int status;
>  	struct edid *edid;
> -	int num = 0;
> -	int ret;
> -
> -	ret = regmap_update_bits(regmap, SII902X_SYS_CTRL_DATA,
> -				 SII902X_SYS_CTRL_DDC_BUS_REQ,
> -				 SII902X_SYS_CTRL_DDC_BUS_REQ);
> -	if (ret)
> -		return ret;
> -
> -	timeout = jiffies +
> -		  msecs_to_jiffies(SII902X_I2C_BUS_ACQUISITION_TIMEOUT_MS);
> -	do {
> -		ret = regmap_read(regmap, SII902X_SYS_CTRL_DATA, &status);
> -		if (ret)
> -			return ret;
> -	} while (!(status & SII902X_SYS_CTRL_DDC_BUS_GRTD) &&
> -		 time_before(jiffies, timeout));
> +	int num = 0, ret;
>  
> -	if (!(status & SII902X_SYS_CTRL_DDC_BUS_GRTD)) {
> -		dev_err(dev, "failed to acquire the i2c bus\n");
> -		return -ETIMEDOUT;
> -	}
> -
> -	ret = regmap_write(regmap, SII902X_SYS_CTRL_DATA, status);
> -	if (ret)
> -		return ret;
> -
> -	edid = drm_get_edid(connector, sii902x->i2c->adapter);
> +	edid = drm_get_edid(connector, sii902x->i2cmux->adapter[0]);
>  	drm_connector_update_edid_property(connector, edid);
>  	if (edid) {
>  		num = drm_add_edid_modes(connector, edid);
> @@ -181,42 +195,6 @@ static int sii902x_get_modes(struct drm_connector *connector)
>  	if (ret)
>  		return ret;
>  
> -	/*
> -	 * Sometimes the I2C bus can stall after failure to use the
> -	 * EDID channel. Retry a few times to see if things clear
> -	 * up, else continue anyway.
> -	 */
> -	retries = 5;
> -	do {
> -		ret = regmap_read(regmap, SII902X_SYS_CTRL_DATA,
> -				  &status);
> -		retries--;
> -	} while (ret && retries);
> -	if (ret)
> -		dev_err(dev, "failed to read status (%d)\n", ret);
> -
> -	ret = regmap_update_bits(regmap, SII902X_SYS_CTRL_DATA,
> -				 SII902X_SYS_CTRL_DDC_BUS_REQ |
> -				 SII902X_SYS_CTRL_DDC_BUS_GRTD, 0);
> -	if (ret)
> -		return ret;
> -
> -	timeout = jiffies +
> -		  msecs_to_jiffies(SII902X_I2C_BUS_ACQUISITION_TIMEOUT_MS);
> -	do {
> -		ret = regmap_read(regmap, SII902X_SYS_CTRL_DATA, &status);
> -		if (ret)
> -			return ret;
> -	} while (status & (SII902X_SYS_CTRL_DDC_BUS_REQ |
> -			   SII902X_SYS_CTRL_DDC_BUS_GRTD) &&
> -		 time_before(jiffies, timeout));
> -
> -	if (status & (SII902X_SYS_CTRL_DDC_BUS_REQ |
> -		      SII902X_SYS_CTRL_DDC_BUS_GRTD)) {
> -		dev_err(dev, "failed to release the i2c bus\n");
> -		return -ETIMEDOUT;
> -	}
> -
>  	return num;
>  }
>  
> @@ -366,6 +344,121 @@ static irqreturn_t sii902x_interrupt(int irq, void *data)
>  	return IRQ_HANDLED;
>  }
>  
> +/*
> + * The purpose of sii902x_i2c_bypass_select is to enable the pass through
> + * mode of the HDMI transmitter. Do not use regmap from within this function,
> + * only use sii902x_*_unlocked functions to read/modify/write registers.
> + * We are holding the parent adapter lock here, keep this in mind before
> + * adding more i2c transactions.
> + *
> + * Also, since SII902X_SYS_CTRL_DATA is used with regmap_update_bits elsewhere
> + * in this driver, we need to make sure that we only touch 0x1A[2:1] from
> + * within sii902x_i2c_bypass_select and sii902x_i2c_bypass_deselect, and that
> + * we leave the remaining bits as we have found them.
> + */
> +static int sii902x_i2c_bypass_select(struct i2c_mux_core *mux, u32 chan_id)
> +{
> +	struct sii902x *sii902x = i2c_mux_priv(mux);
> +	struct device *dev = &sii902x->i2c->dev;
> +	unsigned long timeout;
> +	u8 status;
> +	int ret;
> +
> +	ret = sii902x_update_bits_unlocked(sii902x->i2c, SII902X_SYS_CTRL_DATA,
> +					   SII902X_SYS_CTRL_DDC_BUS_REQ,
> +					   SII902X_SYS_CTRL_DDC_BUS_REQ);
> +	if (ret)
> +		return ret;
> +
> +	timeout = jiffies +
> +		  msecs_to_jiffies(SII902X_I2C_BUS_ACQUISITION_TIMEOUT_MS);
> +	do {
> +		ret = sii902x_read_unlocked(sii902x->i2c, SII902X_SYS_CTRL_DATA,
> +					    &status);
> +		if (ret)
> +			return ret;
> +	} while (!(status & SII902X_SYS_CTRL_DDC_BUS_GRTD) &&
> +		 time_before(jiffies, timeout));
> +
> +	if (!(status & SII902X_SYS_CTRL_DDC_BUS_GRTD)) {
> +		dev_err(dev, "Failed to acquire the i2c bus\n");
> +		return -ETIMEDOUT;
> +	}
> +
> +	return sii902x_write_unlocked(sii902x->i2c, SII902X_SYS_CTRL_DATA,
> +				      status);
> +}
> +
> +/*
> + * The purpose of sii902x_i2c_bypass_deselect is to disable the pass through
> + * mode of the HDMI transmitter. Do not use regmap from within this function,
> + * only use sii902x_*_unlocked functions to read/modify/write registers.
> + * We are holding the parent adapter lock here, keep this in mind before
> + * adding more i2c transactions.
> + *
> + * Also, since SII902X_SYS_CTRL_DATA is used with regmap_update_bits elsewhere
> + * in this driver, we need to make sure that we only touch 0x1A[2:1] from
> + * within sii902x_i2c_bypass_select and sii902x_i2c_bypass_deselect, and that
> + * we leave the remaining bits as we have found them.
> + */
> +static int sii902x_i2c_bypass_deselect(struct i2c_mux_core *mux, u32 chan_id)
> +{
> +	struct sii902x *sii902x = i2c_mux_priv(mux);
> +	struct device *dev = &sii902x->i2c->dev;
> +	unsigned long timeout;
> +	unsigned int retries;
> +	u8 status;
> +	int ret;
> +
> +	/*
> +	 * When the HDMI transmitter is in pass through mode, we need an
> +	 * (undocumented) additional delay between STOP and START conditions
> +	 * to guarantee the bus won't get stuck.
> +	 */
> +	udelay(30);
> +
> +	/*
> +	 * Sometimes the I2C bus can stall after failure to use the
> +	 * EDID channel. Retry a few times to see if things clear
> +	 * up, else continue anyway.
> +	 */
> +	retries = 5;
> +	do {
> +		ret = sii902x_read_unlocked(sii902x->i2c, SII902X_SYS_CTRL_DATA,
> +					    &status);
> +		retries--;
> +	} while (ret && retries);
> +	if (ret) {
> +		dev_err(dev, "failed to read status (%d)\n", ret);
> +		return ret;
> +	}
> +
> +	ret = sii902x_update_bits_unlocked(sii902x->i2c, SII902X_SYS_CTRL_DATA,
> +					   SII902X_SYS_CTRL_DDC_BUS_REQ |
> +					   SII902X_SYS_CTRL_DDC_BUS_GRTD, 0);
> +	if (ret)
> +		return ret;
> +
> +	timeout = jiffies +
> +		  msecs_to_jiffies(SII902X_I2C_BUS_ACQUISITION_TIMEOUT_MS);
> +	do {
> +		ret = sii902x_read_unlocked(sii902x->i2c, SII902X_SYS_CTRL_DATA,
> +					    &status);
> +		if (ret)
> +			return ret;
> +	} while (status & (SII902X_SYS_CTRL_DDC_BUS_REQ |
> +			   SII902X_SYS_CTRL_DDC_BUS_GRTD) &&
> +		 time_before(jiffies, timeout));
> +
> +	if (status & (SII902X_SYS_CTRL_DDC_BUS_REQ |
> +		      SII902X_SYS_CTRL_DDC_BUS_GRTD)) {
> +		dev_err(dev, "failed to release the i2c bus\n");
> +		return -ETIMEDOUT;
> +	}
> +
> +	return 0;
> +}
> +
>  static int sii902x_probe(struct i2c_client *client,
>  			 const struct i2c_device_id *id)
>  {
> @@ -375,6 +468,13 @@ static int sii902x_probe(struct i2c_client *client,
>  	u8 chipid[4];
>  	int ret;
>  
> +	ret = i2c_check_functionality(client->adapter,
> +				      I2C_FUNC_SMBUS_BYTE_DATA);
> +	if (!ret) {
> +		dev_err(dev, "I2C adapter not suitable\n");
> +		return -EIO;
> +	}
> +
>  	sii902x = devm_kzalloc(dev, sizeof(*sii902x), GFP_KERNEL);
>  	if (!sii902x)
>  		return -ENOMEM;
> @@ -433,7 +533,15 @@ static int sii902x_probe(struct i2c_client *client,
>  
>  	i2c_set_clientdata(client, sii902x);
>  
> -	return 0;
> +	sii902x->i2cmux = i2c_mux_alloc(client->adapter, dev,
> +					1, 0, I2C_MUX_GATE,
> +					sii902x_i2c_bypass_select,
> +					sii902x_i2c_bypass_deselect);
> +	if (!sii902x->i2cmux)
> +		return -ENOMEM;
> +
> +	sii902x->i2cmux->priv = sii902x;
> +	return i2c_mux_add_adapter(sii902x->i2cmux, 0, 0, 0);
>  }
>  
>  static int sii902x_remove(struct i2c_client *client)
> @@ -441,6 +549,7 @@ static int sii902x_remove(struct i2c_client *client)
>  {
>  	struct sii902x *sii902x = i2c_get_clientdata(client);
>  
> +	i2c_mux_del_adapters(sii902x->i2cmux);
>  	drm_bridge_remove(&sii902x->bridge);
>  
>  	return 0;

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