Commit 79465e0f authored by Thierry Reding's avatar Thierry Reding
Browse files

drm/dp: Add helper to get post-cursor adjustments 



If the transmitter supports pre-emphasis post cursor2 the sink will
request adjustments in a similar way to how it requests adjustments to
the voltage swing and pre-emphasis settings.

Add a helper to extract these adjustments on a per-lane basis from the
DPCD link status.

Reviewed-by: default avatarPhilipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: default avatarLyude Paul <lyude@redhat.com>
Signed-off-by: default avatarThierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191021143437.1477719-8-thierry.reding@gmail.com
parent fc6b4204

drivers/gpu/drm/drm_dp_helper.c

+10 −0
Original line number Diff line number Diff line
@@ -120,6 +120,16 @@ u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SI 
}

EXPORT_SYMBOL(drm_dp_get_adjust_request_pre_emphasis);



u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE],

					 unsigned int lane)

{

	unsigned int offset = DP_ADJUST_REQUEST_POST_CURSOR2;

	u8 value = dp_link_status(link_status, offset);



	return (value >> (lane << 1)) & 0x3;

}

EXPORT_SYMBOL(drm_dp_get_adjust_request_post_cursor);



void drm_dp_link_train_clock_recovery_delay(const u8 dpcd[DP_RECEIVER_CAP_SIZE])

{

	unsigned long rd_interval = dpcd[DP_TRAINING_AUX_RD_INTERVAL] &

include/drm/drm_dp_helper.h

+10 −0
Original line number Diff line number Diff line
@@ -605,6 +605,14 @@ 
# define DP_ADJUST_PRE_EMPHASIS_LANE1_SHIFT  6



#define DP_ADJUST_REQUEST_POST_CURSOR2      0x20c

# define DP_ADJUST_POST_CURSOR2_LANE0_MASK  0x03

# define DP_ADJUST_POST_CURSOR2_LANE0_SHIFT 0

# define DP_ADJUST_POST_CURSOR2_LANE1_MASK  0x0c

# define DP_ADJUST_POST_CURSOR2_LANE1_SHIFT 2

# define DP_ADJUST_POST_CURSOR2_LANE2_MASK  0x30

# define DP_ADJUST_POST_CURSOR2_LANE2_SHIFT 4

# define DP_ADJUST_POST_CURSOR2_LANE3_MASK  0xc0

# define DP_ADJUST_POST_CURSOR2_LANE3_SHIFT 6



#define DP_TEST_REQUEST			    0x218

# define DP_TEST_LINK_TRAINING		    (1 << 0)
@@ -1122,6 +1130,8 @@ u8 drm_dp_get_adjust_request_voltage(const u8 link_status[DP_LINK_STATUS_SIZE], 
				     int lane);

u8 drm_dp_get_adjust_request_pre_emphasis(const u8 link_status[DP_LINK_STATUS_SIZE],

					  int lane);

u8 drm_dp_get_adjust_request_post_cursor(const u8 link_status[DP_LINK_STATUS_SIZE],

					 unsigned int lane);



#define DP_BRANCH_OUI_HEADER_SIZE	0xc

#define DP_RECEIVER_CAP_SIZE		0xf

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