[PATCH 1/3] drm: add support for DisplayPort CEC-Tunneling-over-AUX
Sean Paul
seanpaul at chromium.org
Thu Aug 10 19:19:59 UTC 2017
On Tue, Jul 11, 2017 at 03:30:09PM +0200, Hans Verkuil wrote:
> From: Hans Verkuil <hans.verkuil at cisco.com>
>
> This adds support for the DisplayPort CEC-Tunneling-over-AUX
> feature that is part of the DisplayPort 1.3 standard.
Hi Hans,
Thank you for the patch, it looks great, I just have a few minor nits below.
>
> Unfortunately, not all DisplayPort/USB-C to HDMI adapters with a
> chip that has this capability actually hook up the CEC pin, so
> even though a CEC device is created, it may not actually work.
Boo :(
>
> Signed-off-by: Hans Verkuil <hans.verkuil at cisco.com>
> ---
> drivers/gpu/drm/Kconfig | 10 ++
> drivers/gpu/drm/Makefile | 1 +
> drivers/gpu/drm/drm_dp_cec.c | 308 +++++++++++++++++++++++++++++++++++++++++++
> include/drm/drm_dp_helper.h | 24 ++++
> 4 files changed, 343 insertions(+)
> create mode 100644 drivers/gpu/drm/drm_dp_cec.c
>
> diff --git a/drivers/gpu/drm/Kconfig b/drivers/gpu/drm/Kconfig
> index 83cb2a88c204..1f2708df5c4e 100644
> --- a/drivers/gpu/drm/Kconfig
> +++ b/drivers/gpu/drm/Kconfig
> @@ -120,6 +120,16 @@ config DRM_LOAD_EDID_FIRMWARE
> default case is N. Details and instructions how to build your own
> EDID data are given in Documentation/EDID/HOWTO.txt.
>
> +config DRM_DP_CEC
> + bool "Enable DisplayPort CEC-Tunneling-over-AUX HDMI support"
> + select CEC_CORE
> + help
> + Choose this option if you want to enable HDMI CEC support for
> + DisplayPort/USB-C to HDMI adapters.
> +
> + Note: not all adapters support this feature, and even for those
> + that do support this they often do not hook up the CEC pin.
> +
> config DRM_TTM
> tristate
> depends on DRM && MMU
> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> index 24a066e1841c..c6552c62049e 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -40,6 +40,7 @@ drm_kms_helper-$(CONFIG_DRM_LOAD_EDID_FIRMWARE) += drm_edid_load.o
> drm_kms_helper-$(CONFIG_DRM_FBDEV_EMULATION) += drm_fb_helper.o
> drm_kms_helper-$(CONFIG_DRM_KMS_CMA_HELPER) += drm_fb_cma_helper.o
> drm_kms_helper-$(CONFIG_DRM_DP_AUX_CHARDEV) += drm_dp_aux_dev.o
> +drm_kms_helper-$(CONFIG_DRM_DP_CEC) += drm_dp_cec.o
>
> obj-$(CONFIG_DRM_KMS_HELPER) += drm_kms_helper.o
> obj-$(CONFIG_DRM_DEBUG_MM_SELFTEST) += selftests/
> diff --git a/drivers/gpu/drm/drm_dp_cec.c b/drivers/gpu/drm/drm_dp_cec.c
> new file mode 100644
> index 000000000000..7f2e298d45c0
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_dp_cec.c
> @@ -0,0 +1,308 @@
> +/*
> + * DisplayPort CEC-Tunneling-over-AUX support
> + *
> + * Copyright 2017 Cisco Systems, Inc. and/or its affiliates. All rights reserved.
> + *
> + * This program is free software; you may redistribute it and/or modify
> + * it under the terms of the GNU General Public License as published by
> + * the Free Software Foundation; version 2 of the License.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
> + * EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
> + * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
> + * NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
> + * BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
> + * ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
> + * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
> + * SOFTWARE.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/slab.h>
> +#include <drm/drm_dp_helper.h>
> +#include <media/cec.h>
> +
> +/*
> + * Unfortunately it turns out that we have a chicken-and-egg situation
> + * here. Quite a few active (mini-)DP-to-HDMI or USB-C-to-HDMI adapters
> + * have a converter chip that supports CEC-Tunneling-over-AUX (usually the
> + * Parade PS176), but they do not wire up the CEC pin, thus making CEC
> + * useless.
> + *
> + * Sadly there is no way for this driver to know this. What happens is
> + * that a /dev/cecX device is created that is isolated and unable to see
> + * any of the other CEC devices. Quite literally the CEC wire is cut
> + * (or in this case, never connected in the first place).
> + *
> + * I suspect that the reason so few adapters support this is that this
> + * tunneling protocol was never supported by any OS. So there was no
> + * easy way of testing it, and no incentive to correctly wire up the
> + * CEC pin.
> + *
> + * Hopefully by creating this driver it will be easier for vendors to
> + * finally fix their adapters and test the CEC functionality.
> + *
> + * I keep a list of known working adapters here:
> + *
> + * https://hverkuil.home.xs4all.nl/cec-status.txt
> + *
> + * Please mail me (hverkuil at xs4all.nl) if you find an adapter that works
> + * and is not yet listed there.
According to the schematics, the Google USB-C -> HDMI adapter[1] has CEC wired
up.
[1]- https://store.google.com/product/usb_type_c_to_hdmi_adapter
> + */
> +
> +/**
> + * DOC: dp cec helpers
> + *
> + * These functions take care of supporting the CEC-Tunneling-over-AUX
> + * feature of DisplayPort-to-HDMI adapters.
> + */
> +
> +static int drm_dp_cec_adap_enable(struct cec_adapter *adap, bool enable)
> +{
> + struct drm_dp_aux *aux = cec_get_drvdata(adap);
> + ssize_t err = 0;
> +
> + if (enable)
> + err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL,
> + DP_CEC_TUNNELING_ENABLE);
> + else
> + err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, 0);
nit: The pattern for this type of thing is usually,
u32 val = 0;
if (enable)
val = DP_CEC_TUNNELING_ENABLE;
err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, val);
> + return (enable && err < 0) ? err : 0;
> +}
> +
> +static int drm_dp_cec_adap_log_addr(struct cec_adapter *adap, u8 addr)
> +{
> + struct drm_dp_aux *aux = cec_get_drvdata(adap);
> + u8 mask[2] = { 0x00, 0x80 };
> + ssize_t err;
> +
> + if (addr != CEC_LOG_ADDR_INVALID) {
Save yourself a bit of work and do:
if (addr == CEC_LOG_ADDR_INVALID)
return 0;
> + u16 la_mask = adap->log_addrs.log_addr_mask;
> +
> + la_mask |= 0x8000 | (1 << addr);
What's the 0x8000? Can you make it a little more clear by doing:
la_mask |= 1 << SOME_DESCRIPTIVE_NAME | (1 << addr);
> + mask[0] = la_mask & 0xff;
> + mask[1] = la_mask >> 8;
> + }
> + err = drm_dp_dpcd_write(aux, DP_CEC_LOGICAL_ADDRESS_MASK, mask, 2);
> + return (addr != CEC_LOG_ADDR_INVALID && err < 0) ? err : 0;
> +}
> +
> +static int drm_dp_cec_adap_transmit(struct cec_adapter *adap, u8 attempts,
> + u32 signal_free_time, struct cec_msg *msg)
> +{
> + struct drm_dp_aux *aux = cec_get_drvdata(adap);
> + unsigned int retries = attempts - 1;
unsigned int retries = min(5, attempts - 1);
> + ssize_t err;
> +
> + err = drm_dp_dpcd_write(aux, DP_CEC_TX_MESSAGE_BUFFER,
> + msg->msg, msg->len);
> + if (err < 0)
> + return err;
> +
> + if (retries > 5)
> + retries = 5;
> + err = drm_dp_dpcd_writeb(aux, DP_CEC_TX_MESSAGE_INFO,
> + (msg->len - 1) | (retries << 4) |
> + DP_CEC_TX_MESSAGE_SEND);
> + return err < 0 ? err : 0;
> +}
> +
> +static int drm_dp_cec_adap_monitor_all_enable(struct cec_adapter *adap,
> + bool enable)
> +{
> + struct drm_dp_aux *aux = cec_get_drvdata(adap);
> + ssize_t err;
> + u8 val;
> +
> + if (!(adap->capabilities & CEC_CAP_MONITOR_ALL))
> + return 0;
> +
> + err = drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CONTROL, &val);
> + if (err >= 0) {
> + if (enable)
> + val |= DP_CEC_SNOOPING_ENABLE;
> + else
> + val &= ~DP_CEC_SNOOPING_ENABLE;
> + err = drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_CONTROL, val);
> + }
> + return (enable && err < 0) ? err : 0;
> +}
> +
> +static void drm_dp_cec_adap_status(struct cec_adapter *adap,
> + struct seq_file *file)
> +{
> + struct drm_dp_aux *aux = cec_get_drvdata(adap);
> + u8 buf[DP_AUX_MAX_PAYLOAD_BYTES];
> + u8 hw_rev;
> +
> + if (drm_dp_dpcd_read(aux, DP_BRANCH_OUI,
> + buf, sizeof(buf)) != sizeof(buf))
> + return;
> + hw_rev = buf[9];
> + buf[9] = 0;
> + seq_printf(file, "OUI: %02x-%02x-%02x\n",
> + buf[0], buf[1], buf[2]);
> + seq_printf(file, "ID: %s\n", buf + 3);
> + seq_printf(file, "HW Rev: %d.%d\n", hw_rev >> 4, hw_rev & 0xf);
> + /*
> + * Show this both in decimal and hex: at least one vendor
> + * always reports this in hex.
> + */
> + seq_printf(file, "FW/SW Rev: %d.%d (0x%02x.0x%02x)\n",
> + buf[10], buf[11], buf[10], buf[11]);
> +}
> +
> +static const struct cec_adap_ops drm_dp_cec_adap_ops = {
> + .adap_enable = drm_dp_cec_adap_enable,
> + .adap_log_addr = drm_dp_cec_adap_log_addr,
> + .adap_transmit = drm_dp_cec_adap_transmit,
> + .adap_monitor_all_enable = drm_dp_cec_adap_monitor_all_enable,
> + .adap_status = drm_dp_cec_adap_status,
> +};
> +
> +static int drm_dp_cec_received(struct drm_dp_aux *aux)
> +{
> + struct cec_adapter *adap = aux->cec_adap;
> + struct cec_msg msg;
> + u8 rx_msg_info;
> + ssize_t err;
> +
> + err = drm_dp_dpcd_readb(aux, DP_CEC_RX_MESSAGE_INFO, &rx_msg_info);
> + if (err < 0)
> + return err;
> + if (!(rx_msg_info & DP_CEC_RX_MESSAGE_ENDED))
> + return 0;
> + msg.len = (rx_msg_info & DP_CEC_RX_MESSAGE_LEN_MASK) + 1;
> + err = drm_dp_dpcd_read(aux, DP_CEC_RX_MESSAGE_BUFFER, msg.msg, msg.len);
> + if (err < 0)
> + return err;
> + cec_received_msg(adap, &msg);
> + return 0;
> +}
> +
> +static int drm_dp_cec_handle_irq(struct drm_dp_aux *aux)
> +{
> + struct cec_adapter *adap = aux->cec_adap;
> + u8 flags;
> + ssize_t err;
> +
> + err = drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, &flags);
> + if (err < 0)
> + return err;
> +
> + if (flags & DP_CEC_RX_MESSAGE_INFO_VALID)
> + drm_dp_cec_received(aux);
> +
> + if (flags & DP_CEC_TX_MESSAGE_SENT)
> + cec_transmit_attempt_done(adap, CEC_TX_STATUS_OK);
> + else if (flags & DP_CEC_TX_LINE_ERROR)
> + cec_transmit_attempt_done(adap, CEC_TX_STATUS_ERROR |
> + CEC_TX_STATUS_MAX_RETRIES);
> + else if (flags &
> + (DP_CEC_TX_ADDRESS_NACK_ERROR | DP_CEC_TX_DATA_NACK_ERROR))
> + cec_transmit_attempt_done(adap, CEC_TX_STATUS_NACK |
> + CEC_TX_STATUS_MAX_RETRIES);
> + drm_dp_dpcd_writeb(aux, DP_CEC_TUNNELING_IRQ_FLAGS, flags);
> + return 0;
> +}
> +
> +/**
> + * drm_dp_cec_irq() - handle CEC interrupt, if any
> + * @aux: DisplayPort AUX channel
> + *
> + * Should be called when handling an IRQ_HPD request. If CEC-tunneling-over-AUX
> + * is present, then it will check for a CEC_IRQ and handle it accordingly.
> + *
> + * Returns true if an interrupt was handled successfully or false otherwise.
> + */
> +bool drm_dp_cec_irq(struct drm_dp_aux *aux)
> +{
> + int attempts = 4;
> + bool handled = false;
> +
> + if (!aux->cec_adap)
> + return false;
> +
> + while (attempts--) {
nit: this seems more natural as a for loop:
for (int attempts = 5; attempts > 0; attempts--)
> + u8 cec_irq;
> + int ret;
> +
> + ret = drm_dp_dpcd_readb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1,
> + &cec_irq);
> + if (ret < 0 || !(cec_irq & DP_CEC_IRQ))
> + break;
> +
> + if (!drm_dp_cec_handle_irq(aux))
> + handled = true;
> +
> + ret = drm_dp_dpcd_writeb(aux, DP_DEVICE_SERVICE_IRQ_VECTOR_ESI1,
> + DP_CEC_IRQ);
> + if (ret < 0)
> + break;
> + }
> + return handled;
> +}
> +EXPORT_SYMBOL(drm_dp_cec_irq);
> +
> +/**
> + * drm_dp_cec_configure_adapter() - configure the CEC adapter
> + * @aux: DisplayPort AUX channel
> + * @name: name of the CEC device
> + * @parent: parent device
> + *
> + * Checks if this is a DisplayPort-to-HDMI adapter that supports
> + * CEC-tunneling-over-AUX, and if so it creates a CEC device.
> + *
> + * If a CEC device was already created, then check if the capabilities
> + * have changed. If not, then do nothing. Otherwise destroy the old
> + * CEC device and create a new CEC device.
> + *
> + * This can happen when one DP-to-HDMI adapter is disconnected and
> + * replaced by another adapter with different CEC capabilities.
> + *
> + * Returns 0 on success or a negative error code on failure.
> + */
> +int drm_dp_cec_configure_adapter(struct drm_dp_aux *aux, const char *name,
> + struct device *parent)
> +{
> + u32 cec_caps = CEC_CAP_LOG_ADDRS | CEC_CAP_TRANSMIT |
> + CEC_CAP_PASSTHROUGH | CEC_CAP_RC | CEC_CAP_NEEDS_HPD;
> + unsigned int num_las = 1;
> + int err;
> + u8 cap;
> +
> + if (drm_dp_dpcd_readb(aux, DP_CEC_TUNNELING_CAPABILITY, &cap) != 1 ||
> + !(cap & DP_CEC_TUNNELING_CAPABLE)) {
> + cec_unregister_adapter(aux->cec_adap);
> + aux->cec_adap = NULL;
> + return -ENODEV;
> + }
> +
> + if (cap & DP_CEC_SNOOPING_CAPABLE)
> + cec_caps |= CEC_CAP_MONITOR_ALL;
> + if (cap & DP_CEC_MULTIPLE_LA_CAPABLE)
> + num_las = CEC_MAX_LOG_ADDRS;
> +
> + if (!IS_ERR_OR_NULL(aux->cec_adap)) {
> + if (aux->cec_adap->capabilities == cec_caps &&
> + aux->cec_adap->available_log_addrs == num_las)
> + return 0;
> + cec_unregister_adapter(aux->cec_adap);
> + }
> +
> + aux->cec_adap = cec_allocate_adapter(&drm_dp_cec_adap_ops,
> + aux, name, cec_caps, num_las);
> + if (IS_ERR(aux->cec_adap)) {
> + err = PTR_ERR(aux->cec_adap);
> + aux->cec_adap = NULL;
> + return err;
> + }
> + err = cec_register_adapter(aux->cec_adap, parent);
> + if (err) {
> + cec_delete_adapter(aux->cec_adap);
> + aux->cec_adap = NULL;
> + }
> + return err;
> +}
> +EXPORT_SYMBOL(drm_dp_cec_configure_adapter);
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index b17476a6909c..0e236dd40b42 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -952,6 +952,8 @@ struct drm_dp_aux_msg {
> size_t size;
> };
>
> +struct cec_adapter;
> +
> /**
> * struct drm_dp_aux - DisplayPort AUX channel
> * @name: user-visible name of this AUX channel and the I2C-over-AUX adapter
> @@ -1010,6 +1012,10 @@ struct drm_dp_aux {
> * @i2c_defer_count: Counts I2C DEFERs, used for DP validation.
> */
> unsigned i2c_defer_count;
> + /**
> + * @cec_adap: the CEC adapter for CEC-Tunneling-over-AUX support.
> + */
> + struct cec_adapter *cec_adap;
> };
>
> ssize_t drm_dp_dpcd_read(struct drm_dp_aux *aux, unsigned int offset,
> @@ -1132,4 +1138,22 @@ drm_dp_has_quirk(const struct drm_dp_desc *desc, enum drm_dp_quirk quirk)
> return desc->quirks & BIT(quirk);
> }
>
> +#ifdef CONFIG_DRM_DP_CEC
> +bool drm_dp_cec_irq(struct drm_dp_aux *aux);
> +int drm_dp_cec_configure_adapter(struct drm_dp_aux *aux, const char *name,
> + struct device *parent);
> +#else
> +static inline bool drm_dp_cec_irq(struct drm_dp_aux *aux)
> +{
> + return false;
> +}
> +
> +static inline int drm_dp_cec_configure_adapter(struct drm_dp_aux *aux,
> + const char *name,
> + struct device *parent)
> +{
> + return -ENODEV;
> +}
> +#endif
> +
> #endif /* _DRM_DP_HELPER_H_ */
> --
> 2.11.0
>
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--
Sean Paul, Software Engineer, Google / Chromium OS
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