Hi!
A handful of nitpicks inline...
On 2018-11-05 14:56, Fabrizio Castro 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@xxxxxxxxxxxxxx>
>
> ---
> v1->v2:
> * Incorporated comments from Peter Rosin
>
> drivers/gpu/drm/bridge/sii902x.c | 256 ++++++++++++++++++++++++++++-----------
> 1 file changed, 188 insertions(+), 68 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/sii902x.c b/drivers/gpu/drm/bridge/sii902x.c
> index e59a135..dd4318b 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@xxxxxxxxx>
> *
> @@ -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));
> -
> - 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;
> + int num = 0, 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 +344,122 @@ 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);
You have omitted failure handling here.
> +
> + 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;
> + }
> +
> + ret = sii902x_write_unlocked(sii902x->i2c, SII902X_SYS_CTRL_DATA,
> + status);
> + if (ret)
> + return ret;
> + return 0;
A plain "return sii902x_write_unlocked(...);" is equivalent.
> +}
> +
> +/*
> + * 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 +469,13 @@ 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;
> @@ -433,6 +534,22 @@ static int sii902x_probe(struct i2c_client *client,
>
> i2c_set_clientdata(client, sii902x);
>
> + sii902x->i2cmux = i2c_mux_alloc(client->adapter, dev,
> + 1, 0, I2C_MUX_GATE,
> + sii902x_i2c_bypass_select,
> + sii902x_i2c_bypass_deselect);
> + if (!sii902x->i2cmux) {
> + dev_err(dev, "failed to allocate I2C mux\n");
The dev_err can be dropped. The only reason for i2c_mux_alloc to
fail is if devm_kzalloc fails, and if that happens you'll get a
better diagnostic directly from that failure. If i2c_mux_alloc
grows some other failure reason in the future, I intend to require
a failure message so that call sites like this can stay neat and
tidy.
> + return -ENOMEM;
> + }
> +
> + sii902x->i2cmux->priv = sii902x;
> + ret = i2c_mux_add_adapter(sii902x->i2cmux, 0, 0, 0);
> + if (ret) {
> + dev_err(dev, "Couldn't add i2c mux adapter\n");
i2c_mux_add_adapter has already reported a better message which it
why this dev_err can be dropped. So, combining with the similar
simplification of the sii902x_write_unlocked "tail call" above, just
do
return i2c_mux_add_adapter(...);
> + return ret;
> + }
> +
> return 0;
> }
>
> @@ -441,6 +558,9 @@ static int sii902x_remove(struct i2c_client *client)
> {
> struct sii902x *sii902x = i2c_get_clientdata(client);
>
> + if (sii902x->i2cmux)
> + i2c_mux_del_adapters(sii902x->i2cmux);
Boris already commented on this, and I agree with his analysis.
Cheers,
Peter
> +
> drm_bridge_remove(&sii902x->bridge);
>
> return 0;
>
