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

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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: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191021143437.1477719-8-thierry.reding@gmail.com
This commit is contained in:
Thierry Reding 2019-10-21 16:34:31 +02:00
parent fc6b42045e
commit 79465e0ffe
2 changed files with 20 additions and 0 deletions
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10
drivers/gpu/drm/drm_dp_helper.c
View File

@ -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] &

10
include/drm/drm_dp_helper.h
View File

@ -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