[PATCH] drm/bridge/sii902x: Fix EDID readback
Peter Rosin
peda at axentia.se
Fri Nov 2 12:26:40 UTC 2018
On 2018-11-02 13:13, 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 at bp.renesas.com>
> ---
> RFC->PATCH:
> * Incorporated Linus Walleij, Peter Rosin, and Mark Brown comments
>
> Thank you guys
>
> drivers/gpu/drm/bridge/sii902x.c | 264 +++++++++++++++++++++++++++++----------
> 1 file changed, 196 insertions(+), 68 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/sii902x.c b/drivers/gpu/drm/bridge/sii902x.c
> index e59a135..4f9d9c7 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 at 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 +89,68 @@ 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)
> +{
> + struct i2c_msg xfer[] = {
> + {
> + .addr = i2c->addr,
> + .flags = 0,
> + .len = 1,
> + .buf = ®,
> + }, {
> + .addr = i2c->addr,
> + .flags = I2C_M_RD,
> + .len = 1,
> + .buf = val,
> + }
> + };
> + unsigned char xfers = ARRAY_SIZE(xfer);
> + int ret, retries = 5;
> +
> + do {
> + ret = __i2c_transfer(i2c->adapter, xfer, xfers);
> + if (ret < 0)
> + return ret;
> + } while (ret != xfers && --retries);
> + return ret == xfers ? 0 : -1;
> +}
> +
> +static int sii902x_write_unlocked(struct i2c_client *i2c, u8 reg, u8 val)
> +{
> + u8 data[2] = {reg, val};
> + struct i2c_msg xfer = {
> + .addr = i2c->addr,
> + .flags = 0,
> + .len = sizeof(data),
> + .buf = data,
> + };
> + int ret, retries = 5;
> +
> + do {
> + ret = __i2c_transfer(i2c->adapter, &xfer, 1);
> + if (ret < 0)
> + return ret;
> + } while (!ret && --retries);
> + return !ret ? -1 : 0;
> +}
> +
> +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 +198,11 @@ 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 +214,6 @@ 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 +363,112 @@ 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.
> + */
> +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);
Here (and also in sii902x_i2c_bypass_deselect) you do a rmw access to the
SII902X_SYS_CTRL_DATA register without coordinating with regmap. Regmap is
also doing rmw accesses to that register in other parts of the driver. I
think you need to either add comment as to why that is safe (maybe other
things make it impossible for the two rmw accesses to cross?), or add the
missing coordination.
> +
> + 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;
> +}
> +
> +/*
> + * 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.
> + */
> +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 +478,12 @@ static int sii902x_probe(struct i2c_client *client,
> u8 chipid[4];
> int ret;
>
> + ret = i2c_check_functionality(client->adapter, I2C_FUNC_I2C);
> + 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 +542,22 @@ 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");
> + 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");
> + return ret;
> + }
> +
> return 0;
> }
>
> @@ -441,6 +566,9 @@ static int sii902x_remove(struct i2c_client *client)
> {
> struct sii902x *sii902x = i2c_get_clientdata(client);
>
> + if (sii902x->i2cmux)
> + i2c_mux_del_adapters(sii902x->i2cmux);
> +
> drm_bridge_remove(&sii902x->bridge);
>
> return 0;
>
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