Hello Peter,
Thank you for your feedback!
> Subject: Re: [PATCH v2] drm/bridge/sii902x: Fix EDID readback
>
> 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.
Will improve that.
>
> > +
> > +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.
Will change
>
> > +}
> > +
> > +/*
> > + * 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.
Will drop
>
> > +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(...);
Will do
>
> > +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.
Me too
Thanks,
Fab
>
> Cheers,
> Peter
>
> > +
> > drm_bridge_remove(&sii902x->bridge);
> >
> > return 0;
> >
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