[Intel-gfx] [PATCH v4 4/5] drm/dp: Allow registering AUX channels as I2C busses
Jani Nikula
jani.nikula at linux.intel.com
Tue Feb 4 10:29:43 CET 2014
On Tue, 21 Jan 2014, Thierry Reding <thierry.reding at gmail.com> 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.
>
> Reviewed-by: Alex Deucher <alexander.deucher at amd.com>
> Reviewed-by: Jani Nikula <jani.nikula at intel.com>
I know I reviewed this already, but here are some more comments based on
converting i915 on top of this...
> Signed-off-by: Thierry Reding <treding at nvidia.com>
> ---
> Changes in v4:
> - fix typo "bitrate" -> "bit rate"
>
> Changes in v3:
> - add back DRM_DEBUG_KMS and DRM_ERROR messages
> - embed i2c_adapter within struct drm_dp_aux
> - fix typo in comment
>
> drivers/gpu/drm/drm_dp_helper.c | 183 ++++++++++++++++++++++++++++++++++++++++
> include/drm/drm_dp_helper.h | 5 ++
> 2 files changed, 188 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index eea15b1414ed..dba4205de274 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -364,6 +364,13 @@ EXPORT_SYMBOL(drm_dp_bw_code_to_link_rate);
> *
> * The .dev field should be set to a pointer to the device that implements
> * the AUX channel.
> + *
> + * An AUX channel can also be used to transport I2C messages to a sink. A
> + * typical application of that is to access an EDID that's present in the
> + * sink device. The .transfer() function can also be used to execute such
> + * transactions. The drm_dp_aux_register_i2c_bus() function registers an
> + * I2C adapter that can be passed to drm_probe_ddc(). Upon removal, drivers
> + * should call drm_dp_aux_unregister_i2c_bus() to remove the I2C adapter.
> */
>
> static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
> @@ -566,3 +573,179 @@ int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)
>
> return 0;
> }
> +
> +/*
> + * I2C-over-AUX implementation
> + */
> +
> +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) {
> + if (err == -EBUSY)
> + continue;
> +
> + DRM_DEBUG_KMS("transaction failed: %d\n", err);
> + 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:
> + DRM_DEBUG_KMS("native nack\n");
> + return -EREMOTEIO;
> +
> + case DP_AUX_NATIVE_REPLY_DEFER:
> + DRM_DEBUG_KMS("native defer");
> + /*
> + * We could check for I2C bit rate capabilities and if
> + * available adjust this interval. We could also be
> + * more careful with DP-to-legacy adapters where a
> + * long legacy cable may force 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:
> + DRM_DEBUG_KMS("I2C nack\n");
> + return -EREMOTEIO;
> +
> + case DP_AUX_I2C_REPLY_DEFER:
> + DRM_DEBUG_KMS("I2C defer\n");
> + 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_aux *aux = adapter->algo_data;
> + unsigned int i, j;
> +
> + for (i = 0; i < num; i++) {
> + struct drm_dp_aux_msg msg;
> + int err;
> +
Should there be a start message similar to the i2c_algo_dp_aux_address()
call in i2c_algo_dp_aux_xfer() here? How would that map out to the
->transfer() function? msg.size = 0?
> + /*
> + * 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.
> + */
Ville suggested this should be up to the drivers to decide. Maybe we
could have an aux->max_i2c_message_size (or similar), set by the
drivers, defaulting to 1, and this would chop up the message as
necessary? This could be a follow-up patch.
> + 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(aux, &msg);
> + if (err < 0)
> + return err;
> + }
> + }
Should there be a stop message similar to the i2c_algo_dp_aux_stop()
call in i2c_algo_dp_aux_xfer() here? Does not seem as crucial as the
start message because DP_AUX_I2C_MOT is handled above.
> +
> + return num;
> +}
> +
> +static const struct i2c_algorithm drm_dp_i2c_algo = {
> + .functionality = drm_dp_i2c_functionality,
> + .master_xfer = drm_dp_i2c_xfer,
> +};
> +
> +/**
> + * drm_dp_aux_register_i2c_bus() - register an I2C adapter for I2C-over-AUX
> + * @aux: DisplayPort AUX channel
> + *
> + * Returns 0 on success or a negative error code on failure.
> + */
> +int drm_dp_aux_register_i2c_bus(struct drm_dp_aux *aux)
> +{
> + aux->ddc.algo = &drm_dp_i2c_algo;
> + aux->ddc.algo_data = aux;
> + aux->ddc.retries = 3;
> +
> + aux->ddc.class = I2C_CLASS_DDC;
> + aux->ddc.owner = THIS_MODULE;
> + aux->ddc.dev.parent = aux->dev;
> + aux->ddc.dev.of_node = aux->dev->of_node;
> +
> + strncpy(aux->ddc.name, dev_name(aux->dev), sizeof(aux->ddc.name));
> +
Should there be something similar to i2c_dp_aux_reset_bus() here like in
i2c_dp_aux_add_bus()?
> + return i2c_add_adapter(&aux->ddc);
> +}
> +EXPORT_SYMBOL(drm_dp_aux_register_i2c_bus);
> +
> +/**
> + * drm_dp_aux_unregister_i2c_bus() - unregister an I2C-over-AUX adapter
> + * @aux: DisplayPort AUX channel
> + */
> +void drm_dp_aux_unregister_i2c_bus(struct drm_dp_aux *aux)
> +{
> + i2c_del_adapter(&aux->ddc);
> +}
> +EXPORT_SYMBOL(drm_dp_aux_unregister_i2c_bus);
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index c7b3c736c40a..4d67bd12089b 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -421,10 +421,12 @@ struct drm_dp_aux_msg {
>
> /**
> * struct drm_dp_aux - DisplayPort AUX channel
> + * @ddc: I2C adapter that can be used for I2C-over-AUX communication
> * @dev: pointer to struct device that is the parent for this AUX channel
> * @transfer: transfers a message representing a single AUX transaction
> */
> struct drm_dp_aux {
> + struct i2c_adapter ddc;
> struct device *dev;
>
> ssize_t (*transfer)(struct drm_dp_aux *aux,
> @@ -485,4 +487,7 @@ 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);
> int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link);
>
> +int drm_dp_aux_register_i2c_bus(struct drm_dp_aux *aux);
> +void drm_dp_aux_unregister_i2c_bus(struct drm_dp_aux *aux);
> +
> #endif /* _DRM_DP_HELPER_H_ */
> --
> 1.8.4.2
>
--
Jani Nikula, Intel Open Source Technology Center
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