Re: [PATCH 1/6] drm/dp_tunnel: Add UHBR tunneling support

[Imre Deak <imre.deak@intel.com>]

Hi Thomas, Maarten, Maxime,

could you please ack merging this patch via the Intel trees? It adds the
DP tunnel register definitions for UHBR link rates and reading/parsing
them, which are then used later in this patchset by the Intel driver.

Thanks,
Imre

On Tue, Jul 14, 2026 at 06:26:55PM +0300, Imre Deak wrote:
> Add the DPCD registers and detection required to support UHBR link rates
> over Thunderbolt tunnels.
> 
> Cc: dri-devel@lists.freedesktop.org
> Signed-off-by: Imre Deak <imre.deak@intel.com>
> ---
>  drivers/gpu/drm/display/drm_dp_tunnel.c | 116 +++++++++++++++++++++++-
>  include/drm/display/drm_dp.h            |  12 +++
>  include/drm/display/drm_dp_tunnel.h     |  21 +++++
>  3 files changed, 148 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/display/drm_dp_tunnel.c b/drivers/gpu/drm/display/drm_dp_tunnel.c
> index 76c6bc84a806f..d29ad4116e641 100644
> --- a/drivers/gpu/drm/display/drm_dp_tunnel.c
> +++ b/drivers/gpu/drm/display/drm_dp_tunnel.c
> @@ -111,6 +111,8 @@
>  	DPTUN_REG(DP_ALLOCATED_BW) | \
>  	DPTUN_REG(DP_TUNNELING_MAX_LINK_RATE) | \
>  	DPTUN_REG(DP_TUNNELING_MAX_LANE_COUNT) | \
> +	DPTUN_REG(DP_TUNNELING_MAIN_LINK_CHANNEL_CODING) | \
> +	DPTUN_REG(DP_TUNNELING_128B132B_LINK_RATE) | \
>  	DPTUN_REG(DP_DPTX_BW_ALLOCATION_MODE_CONTROL))
>  
>  static const DECLARE_BITMAP(dptun_info_regs, 64) = {
> @@ -140,11 +142,14 @@ struct drm_dp_tunnel {
>  	int estimated_bw;
>  	int allocated_bw;
>  
> +	u8 dprx_128b132b_rates;
>  	int max_dprx_rate;
>  	u8 max_dprx_lane_count;
>  
>  	u8 adapter_id;
>  
> +	bool dprx_128b132b_support:1;
> +	bool dprx_128b132b_lane0_mapping_support:1;
>  	bool bw_alloc_supported:1;
>  	bool bw_alloc_enabled:1;
>  	bool has_io_error:1;
> @@ -260,9 +265,46 @@ static int tunnel_reg_bw_granularity(const struct drm_dp_tunnel_regs *regs)
>  	return (250000 << gr) / 8;
>  }
>  
> +static bool tunnel_reg_dprx_128b132b_support(const struct drm_dp_tunnel_regs *regs)
> +{
> +	return tunnel_reg(regs, DP_TUNNELING_MAIN_LINK_CHANNEL_CODING) & DP_128B132B_DP_SUPPORTED;
> +}
> +
> +static bool tunnel_reg_dprx_128b132b_lane0_mapping_support(const struct drm_dp_tunnel_regs *regs)
> +{
> +	return tunnel_reg(regs, DP_TUNNELING_128B132B_LINK_RATE) &
> +	       DP_TUNNELING_128B132B_LL_LANE0_MAPPING_SUPPORT;
> +}
> +
> +static u8 tunnel_reg_dprx_128b132b_rates(const struct drm_dp_tunnel_regs *regs)
> +{
> +	if (!tunnel_reg_dprx_128b132b_support(regs))
> +		return 0;
> +
> +	return tunnel_reg(regs, DP_TUNNELING_128B132B_LINK_RATE) &
> +	       DP_TUNNELING_128B132B_LINK_RATE_MASK;
> +}
> +
> +static u8 max_128b132b_rate(u8 rates)
> +{
> +	if (rates & DP_TUNNELING_20GBPS_PER_LANE_SUPPORT)
> +		return DP_TUNNELING_20GBPS_PER_LANE_SUPPORT;
> +	else if (rates & DP_TUNNELING_13_5GBPS_PER_LANE_SUPPORT)
> +		return DP_TUNNELING_13_5GBPS_PER_LANE_SUPPORT;
> +	else if (rates & DP_TUNNELING_10GBPS_PER_LANE_SUPPORT)
> +		return DP_TUNNELING_10GBPS_PER_LANE_SUPPORT;
> +
> +	WARN_ON(rates);
> +
> +	return 0;
> +}
> +
>  static int tunnel_reg_max_dprx_rate(const struct drm_dp_tunnel_regs *regs)
>  {
> -	u8 bw_code = tunnel_reg(regs, DP_TUNNELING_MAX_LINK_RATE);
> +	u8 bw_code = max_128b132b_rate(tunnel_reg_dprx_128b132b_rates(regs));
> +
> +	if (!bw_code)
> +		bw_code = tunnel_reg(regs, DP_TUNNELING_MAX_LINK_RATE);
>  
>  	return drm_dp_bw_code_to_link_rate(bw_code);
>  }
> @@ -706,6 +748,23 @@ static bool update_dprx_caps(struct drm_dp_tunnel *tunnel, const struct drm_dp_t
>  {
>  	bool changed = false;
>  
> +	if (tunnel_reg_dprx_128b132b_support(regs) != tunnel->dprx_128b132b_support) {
> +		tunnel->dprx_128b132b_support = tunnel_reg_dprx_128b132b_support(regs);
> +		changed = true;
> +	}
> +
> +	if (tunnel_reg_dprx_128b132b_lane0_mapping_support(regs) !=
> +	    tunnel->dprx_128b132b_lane0_mapping_support) {
> +		tunnel->dprx_128b132b_lane0_mapping_support =
> +			tunnel_reg_dprx_128b132b_lane0_mapping_support(regs);
> +		changed = true;
> +	}
> +
> +	if (tunnel_reg_dprx_128b132b_rates(regs) != tunnel->dprx_128b132b_rates) {
> +		tunnel->dprx_128b132b_rates = tunnel_reg_dprx_128b132b_rates(regs);
> +		changed = true;
> +	}
> +
>  	if (tunnel_reg_max_dprx_rate(regs) != tunnel->max_dprx_rate) {
>  		tunnel->max_dprx_rate = tunnel_reg_max_dprx_rate(regs);
>  		changed = true;
> @@ -1331,6 +1390,61 @@ int drm_dp_tunnel_handle_irq(struct drm_dp_tunnel_mgr *mgr, struct drm_dp_aux *a
>  }
>  EXPORT_SYMBOL(drm_dp_tunnel_handle_irq);
>  
> +/**
> + * drm_dp_tunnel_128b132b_supported - Query if 128b132b is supported by the tunnel's DPRX
> + * @tunnel: Tunnel object
> + *
> + * The function is used to query if 128b132b is supported by the DPRX connected
> + * to @tunnel.
> + *
> + * Returns %true if 128b132b is supported by the DPRX.
> + */
> +bool drm_dp_tunnel_128b132b_supported(const struct drm_dp_tunnel *tunnel)
> +{
> +	return tunnel->dprx_128b132b_support;
> +}
> +EXPORT_SYMBOL(drm_dp_tunnel_128b132b_supported);
> +
> +/**
> + * drm_dp_tunnel_128b132b_lane0_mapping_supported - Check 128b/132b lane 0 mapping support
> + * @tunnel: Tunnel object
> + *
> + * Check whether the DP-out adapter always maps lane 0 as expected by the
> + * DPRX on a tunneled 128b/132b link. If the function returns %true, one- and
> + * two-lane configurations with UHBR link rates can always be used. If it
> + * returns %false, using one or two lanes with UHBR link rates may cause a
> + * lane-count conversion failure in the DPRX, requiring corrective action by
> + * the source during link training. See DP Standard v2.1b, section
> + * 3.5.2.16.3, 128b/132b DPRX Lane Count Conversion Failure Indication and
> + * Corrective Action.
> + *
> + * A four-lane configuration can always be used, provided that the DPRX
> + * supports it, regardless of the function's return value.
> + *
> + * Returns %true if the DP-out adapter supports the 128b/132b lane 0 mapping.
> + */
> +bool drm_dp_tunnel_128b132b_lane0_mapping_supported(const struct drm_dp_tunnel *tunnel)
> +{
> +	return tunnel->dprx_128b132b_lane0_mapping_support;
> +}
> +EXPORT_SYMBOL(drm_dp_tunnel_128b132b_lane0_mapping_supported);
> +
> +/**
> + * drm_dp_tunnel_128b132b_dprx_rates - Query the supported 128b132b rates of the tunnel's DPRX
> + * @tunnel: Tunnel object
> + *
> + * The function is used to query the supported 128b132b rates of the DPRX connected
> + * to @tunnel. Note that the related DP_128B132B_SUPPROTED_LINK_RATES DPCD
> + * register will indicate no supported 128B132B rates for a tunneled DPRX.
> + *
> + * Returns the mask of supported 128b132b rates.
> + */
> +u8 drm_dp_tunnel_128b132b_dprx_rates(const struct drm_dp_tunnel *tunnel)
> +{
> +	return tunnel->dprx_128b132b_rates;
> +}
> +EXPORT_SYMBOL(drm_dp_tunnel_128b132b_dprx_rates);
> +
>  /**
>   * drm_dp_tunnel_max_dprx_rate - Query the maximum rate of the tunnel's DPRX
>   * @tunnel: Tunnel object
> diff --git a/include/drm/display/drm_dp.h b/include/drm/display/drm_dp.h
> index 7154216e0aff9..8b0ca36083dd1 100644
> --- a/include/drm/display/drm_dp.h
> +++ b/include/drm/display/drm_dp.h
> @@ -1506,6 +1506,18 @@
>  #define DP_TUNNELING_MAX_LANE_COUNT			0xe0029
>  #define  DP_TUNNELING_MAX_LANE_COUNT_MASK		0x1f
>  
> +#define DP_TUNNELING_MAIN_LINK_CHANNEL_CODING		0xe002b
> +#define  DP_128B132B_DP_SUPPORTED			(1 << 0)
> +
> +#define DP_TUNNELING_128B132B_LINK_RATE			0xe002c
> +#define  DP_TUNNELING_13_5GBPS_PER_LANE_SUPPORT		(1 << 2)
> +#define  DP_TUNNELING_20GBPS_PER_LANE_SUPPORT		(1 << 1)
> +#define  DP_TUNNELING_10GBPS_PER_LANE_SUPPORT		(1 << 0)
> +#define  DP_TUNNELING_128B132B_LINK_RATE_MASK		(DP_TUNNELING_10GBPS_PER_LANE_SUPPORT | \
> +							 DP_TUNNELING_13_5GBPS_PER_LANE_SUPPORT | \
> +							 DP_TUNNELING_20GBPS_PER_LANE_SUPPORT)
> +#define  DP_TUNNELING_128B132B_LL_LANE0_MAPPING_SUPPORT	(1 << 7)
> +
>  #define DP_DPTX_BW_ALLOCATION_MODE_CONTROL		0xe0030
>  #define  DP_DISPLAY_DRIVER_BW_ALLOCATION_MODE_ENABLE	(1 << 7)
>  #define  DP_UNMASK_BW_ALLOCATION_IRQ			(1 << 6)
> diff --git a/include/drm/display/drm_dp_tunnel.h b/include/drm/display/drm_dp_tunnel.h
> index 57f5e90ba8fda..b5e665560a47e 100644
> --- a/include/drm/display/drm_dp_tunnel.h
> +++ b/include/drm/display/drm_dp_tunnel.h
> @@ -63,6 +63,9 @@ void drm_dp_tunnel_set_io_error(struct drm_dp_tunnel *tunnel);
>  int drm_dp_tunnel_handle_irq(struct drm_dp_tunnel_mgr *mgr,
>  			     struct drm_dp_aux *aux);
>  
> +bool drm_dp_tunnel_128b132b_supported(const struct drm_dp_tunnel *tunnel);
> +bool drm_dp_tunnel_128b132b_lane0_mapping_supported(const struct drm_dp_tunnel *tunnel);
> +u8 drm_dp_tunnel_128b132b_dprx_rates(const struct drm_dp_tunnel *tunnel);
>  int drm_dp_tunnel_max_dprx_rate(const struct drm_dp_tunnel *tunnel);
>  int drm_dp_tunnel_max_dprx_lane_count(const struct drm_dp_tunnel *tunnel);
>  int drm_dp_tunnel_available_bw(const struct drm_dp_tunnel *tunnel);
> @@ -173,6 +176,24 @@ drm_dp_tunnel_handle_irq(struct drm_dp_tunnel_mgr *mgr,
>  	return -EOPNOTSUPP;
>  }
>  
> +static inline bool
> +drm_dp_tunnel_128b132b_supported(const struct drm_dp_tunnel *tunnel)
> +{
> +	return false;
> +}
> +
> +static inline bool
> +drm_dp_tunnel_128b132b_lane0_mapping_supported(const struct drm_dp_tunnel *tunnel)
> +{
> +	return false;
> +}
> +
> +static inline u8
> +drm_dp_tunnel_128b132b_dprx_rates(const struct drm_dp_tunnel *tunnel)
> +{
> +	return 0;
> +}
> +
>  static inline int
>  drm_dp_tunnel_max_dprx_rate(const struct drm_dp_tunnel *tunnel)
>  {
> -- 
> 2.49.1
>