[PATCH v2 4/4] drm/dp: Allow registering AUX channels as I2C busses
Daniel Vetter
daniel at ffwll.ch
Wed Dec 18 00:52:47 PST 2013
On Tue, Dec 17, 2013 at 05:20:07PM +0100, Thierry Reding wrote:
> Implements an I2C-over-AUX I2C adapter on top of the generic drm_dp_aux
> infrastructure. It extracts the retry logic from existing drivers, which
> should help in porting those drivers to this new helper.
>
> Signed-off-by: Thierry Reding <treding at nvidia.com>
> ---
> drivers/gpu/drm/drm_dp_helper.c | 178 ++++++++++++++++++++++++++++++++++++++++
> include/drm/drm_dp_helper.h | 4 +
> 2 files changed, 182 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 01a8173c6e83..8a64cf8ac8cc 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -555,3 +555,181 @@ int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link)
>
> return 0;
> }
> +
> +/*
> + * I2C-over-AUX implementation
> + */
> +
> +struct drm_dp_i2c_adapter {
> + struct i2c_adapter adapter;
> + struct drm_dp_aux *aux;
> +};
I'd just embedded an i2c adapter into the drm_dp_aux structure - I think
drivers always want such a thing. Then maybe rename the setup function
from add to register_i2c_bus or so. For smoother transition drivers can
always store a pointer to this i2c_adapter somewhere more convenient for
them.
-Daniel
> +
> +static u32 drm_dp_i2c_functionality(struct i2c_adapter *adapter)
> +{
> + return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL |
> + I2C_FUNC_SMBUS_READ_BLOCK_DATA |
> + I2C_FUNC_SMBUS_BLOCK_PROC_CALL |
> + I2C_FUNC_10BIT_ADDR;
> +}
> +
> +/*
> + * Transfer a single I2C-over-AUX message and handle various error conditions,
> + * retrying the transaction as appropriate.
> + */
> +static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
> +{
> + unsigned int retry;
> + int err;
> +
> + /*
> + * DP1.2 sections 2.7.7.1.5.6.1 and 2.7.7.1.6.6.1: A DP Source device
> + * is required to retry at least seven times upon receiving AUX_DEFER
> + * before giving up the AUX transaction.
> + */
> + for (retry = 0; retry < 7; retry++) {
> + err = aux->transfer(aux, msg);
> + if (err < 0)
> + return err;
> +
> + switch (msg->reply & DP_AUX_NATIVE_REPLY_MASK) {
> + case DP_AUX_NATIVE_REPLY_ACK:
> + /*
> + * For I2C-over-AUX transactions this isn't enough, we
> + * need to check for the I2C ACK reply.
> + */
> + break;
> +
> + case DP_AUX_NATIVE_REPLY_NACK:
> + return -EREMOTEIO;
> +
> + case DP_AUX_NATIVE_REPLY_DEFER:
> + /*
> + * We could check for I2C bitrate capabilities and if
> + * available adjust this interval. We could also be
> + * more careful with DP-to-legacy adapters where a
> + * long legacy cable may forc very low I2C bit rates.
> + *
> + * For now just defer for long enough to hopefully be
> + * safe for all use-cases.
> + */
> + usleep_range(500, 600);
> + continue;
> +
> + default:
> + DRM_ERROR("invalid native reply %#04x\n", msg->reply);
> + return -EREMOTEIO;
> + }
> +
> + switch (msg->reply & DP_AUX_I2C_REPLY_MASK) {
> + case DP_AUX_I2C_REPLY_ACK:
> + /*
> + * Both native ACK and I2C ACK replies received. We
> + * can assume the transfer was successful.
> + */
> + return 0;
> +
> + case DP_AUX_I2C_REPLY_NACK:
> + return -EREMOTEIO;
> +
> + case DP_AUX_I2C_REPLY_DEFER:
> + usleep_range(400, 500);
> + continue;
> +
> + default:
> + DRM_ERROR("invalid I2C reply %#04x\n", msg->reply);
> + return -EREMOTEIO;
> + }
> + }
> +
> + DRM_ERROR("too many retries, giving up\n");
> + return -EREMOTEIO;
> +}
> +
> +static int drm_dp_i2c_xfer(struct i2c_adapter *adapter, struct i2c_msg *msgs,
> + int num)
> +{
> + struct drm_dp_i2c_adapter *dp = adapter->algo_data;
> + unsigned int i, j;
> +
> + for (i = 0; i < num; i++) {
> + struct drm_dp_aux_msg msg;
> + int err;
> +
> + /*
> + * Many hardware implementations support FIFOs larger than a
> + * single byte, but it has been empirically determined that
> + * transferring data in larger chunks can actually lead to
> + * decreased performance. Therefore each message is simply
> + * transferred byte-by-byte.
> + */
> + for (j = 0; j < msgs[i].len; j++) {
> + memset(&msg, 0, sizeof(msg));
> + msg.address = msgs[i].addr;
> +
> + msg.request = (msgs[i].flags & I2C_M_RD) ?
> + DP_AUX_I2C_READ :
> + DP_AUX_I2C_WRITE;
> +
> + /*
> + * All messages except the last one are middle-of-
> + * transfer messages.
> + */
> + if (j < msgs[i].len - 1)
> + msg.request |= DP_AUX_I2C_MOT;
> +
> + msg.buffer = msgs[i].buf + j;
> + msg.size = 1;
> +
> + err = drm_dp_i2c_do_msg(dp->aux, &msg);
> + if (err < 0)
> + return err;
> + }
> + }
> +
> + return num;
> +}
> +
> +static const struct i2c_algorithm drm_dp_i2c_algo = {
> + .functionality = drm_dp_i2c_functionality,
> + .master_xfer = drm_dp_i2c_xfer,
> +};
> +
> +/**
> + * drm_dp_add_i2c_bus() - register an I2C adapter for I2C-over-AUX access
> + * @aux: DisplayPort AUX channel
> + *
> + * Returns a pointer to an I2C adapter on success or an ERR_PTR()-encoded
> + * error code on failure.
> + */
> +struct i2c_adapter *drm_dp_add_i2c_bus(struct drm_dp_aux *aux)
> +{
> + struct drm_dp_i2c_adapter *adapter;
> + int err;
> +
> + adapter = kzalloc(sizeof(*adapter), GFP_KERNEL);
> + if (!adapter)
> + return ERR_PTR(-ENOMEM);
> +
> + adapter->adapter.algo = &drm_dp_i2c_algo;
> + adapter->adapter.algo_data = adapter;
> + adapter->adapter.retries = 3;
> + adapter->aux = aux;
> +
> + adapter->adapter.class = I2C_CLASS_DDC;
> + adapter->adapter.owner = THIS_MODULE;
> + adapter->adapter.dev.parent = aux->dev;
> + adapter->adapter.dev.of_node = aux->dev->of_node;
> +
> + strncpy(adapter->adapter.name, dev_name(aux->dev),
> + sizeof(adapter->adapter.name));
> +
> + err = i2c_add_adapter(&adapter->adapter);
> + if (err < 0) {
> + kfree(adapter);
> + return ERR_PTR(err);
> + }
> +
> + return &adapter->adapter;
> +}
> +EXPORT_SYMBOL(drm_dp_add_i2c_bus);
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index bad9ee11a2e2..c4acdbc2a172 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -423,6 +423,8 @@ struct drm_dp_aux_msg {
> * @transfer: transfers a message representing a single AUX transaction
> */
> struct drm_dp_aux {
> + struct device *dev;
> +
> ssize_t (*transfer)(struct drm_dp_aux *aux,
> struct drm_dp_aux_msg *msg);
> };
> @@ -494,4 +496,6 @@ int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link);
> */
> int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link);
>
> +struct i2c_adapter *drm_dp_add_i2c_bus(struct drm_dp_aux *aux);
> +
> #endif /* _DRM_DP_HELPER_H_ */
> --
> 1.8.4.2
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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