Some DP dongles in particular seem to be fussy about too large
link M/N values. Set specific value for N divider can resolve
this issue per dongle vendor's comment. So configure N as
constant value (0x8000) to instead of reduce M/N formula when
specific DP dongle connected.
v2: add more comments for issue description and fix typo.
v3: add lost commit messages back for version 2
Cc: Jani Nikula <jani.nik...@intel.com>
Cc: Cooper Chiou <cooper.ch...@intel.com>
Cc: Matt Atwood <matthew.s.atw...@intel.com>
Cc: Maarten Lankhorst <maarten.lankho...@linux.intel.com>
Cc: Dhinakaran Pandiyan <dhinakaran.pandi...@intel.com>
Cc: Clint Taylor <clinton.a.tay...@intel.com>
Signed-off-by: Lee, Shawn C <shawn.c....@intel.com>
---
drivers/gpu/drm/drm_dp_helper.c | 2 +-
drivers/gpu/drm/i915/intel_display.c | 28 +++++++++++++---------------
drivers/gpu/drm/i915/intel_display.h | 2 +-
drivers/gpu/drm/i915/intel_dp.c | 8 ++++----
drivers/gpu/drm/i915/intel_dp_mst.c | 6 +++---
include/drm/drm_dp_helper.h | 6 +++---
6 files changed, 25 insertions(+), 27 deletions(-)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 0362c645d96e..f3a7563eb8a1 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -1269,7 +1269,7 @@ struct dpcd_quirk {
static const struct dpcd_quirk dpcd_quirk_list[] = {
/* Analogix 7737 needs reduced M and N at HBR2 link rates */
- { OUI(0x00, 0x22, 0xb9), DEVICE_ID_ANY, true,
BIT(DP_DPCD_QUIRK_LIMITED_M_N) },
+ { OUI(0x00, 0x22, 0xb9), DEVICE_ID_ANY, true,
BIT(DP_DPCD_QUIRK_CONSTANT_N) },
};
#undef OUI
diff --git a/drivers/gpu/drm/i915/intel_display.c
b/drivers/gpu/drm/i915/intel_display.c
index ec3e24f07486..da0c7fbef3ef 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -6680,22 +6680,20 @@ intel_reduce_m_n_ratio(uint32_t *num, uint32_t *den)
static void compute_m_n(unsigned int m, unsigned int n,
uint32_t *ret_m, uint32_t *ret_n,
- bool reduce_m_n)
+ bool constant_n)
{
/*
- * Reduce M/N as much as possible without loss in precision. Several DP
- * dongles in particular seem to be fussy about too large *link* M/N
- * values. The passed in values are more likely to have the least
- * significant bits zero than M after rounding below, so do this first.
+ * Several DP dongles in particular seem to be fussy about
+ * too large link M/N values. Give N value as 0x8000 that
+ * should be acceptable by specific devices. 0x8000 is the
+ * specified fixed N value for asynchronous clock mode,
+ * which the devices expect also in synchronous clock mode.
*/
- if (reduce_m_n) {
- while ((m & 1) == 0 && (n & 1) == 0) {
- m >>= 1;
- n >>= 1;
- }
- }
+ if (constant_n)
+ *ret_n = 0x8000;
+ else
+ *ret_n = min_t(unsigned int, roundup_pow_of_two(n),
DATA_LINK_N_MAX);
- *ret_n = min_t(unsigned int, roundup_pow_of_two(n), DATA_LINK_N_MAX);
*ret_m = div_u64((uint64_t) m * *ret_n, n);
intel_reduce_m_n_ratio(ret_m, ret_n);
}
@@ -6704,18 +6702,18 @@ void
intel_link_compute_m_n(int bits_per_pixel, int nlanes,
int pixel_clock, int link_clock,
struct intel_link_m_n *m_n,
- bool reduce_m_n)
+ bool constant_n)
{
m_n->tu = 64;
compute_m_n(bits_per_pixel * pixel_clock,
link_clock * nlanes * 8,
&m_n->gmch_m, &m_n->gmch_n,
- reduce_m_n);
+ constant_n);
compute_m_n(pixel_clock, link_clock,
&m_n->link_m, &m_n->link_n,
- reduce_m_n);
+ constant_n);
}
static inline bool intel_panel_use_ssc(struct drm_i915_private *dev_priv)
diff --git a/drivers/gpu/drm/i915/intel_display.h
b/drivers/gpu/drm/i915/intel_display.h
index 43f080c6538d..8e8bd5eed2c2 100644
--- a/drivers/gpu/drm/i915/intel_display.h
+++ b/drivers/gpu/drm/i915/intel_display.h
@@ -379,7 +379,7 @@ struct intel_link_m_n {
void intel_link_compute_m_n(int bpp, int nlanes,
int pixel_clock, int link_clock,
struct intel_link_m_n *m_n,
- bool reduce_m_n);
+ bool constant_n);
bool is_ccs_modifier(u64 modifier);
#endif
diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
index 436c22de33b6..6b4c19123f2a 100644
--- a/drivers/gpu/drm/i915/intel_dp.c
+++ b/drivers/gpu/drm/i915/intel_dp.c
@@ -1998,8 +1998,8 @@ intel_dp_compute_config(struct intel_encoder *encoder,
struct intel_connector *intel_connector = intel_dp->attached_connector;
struct intel_digital_connector_state *intel_conn_state =
to_intel_digital_connector_state(conn_state);
- bool reduce_m_n = drm_dp_has_quirk(&intel_dp->desc,
- DP_DPCD_QUIRK_LIMITED_M_N);
+ bool constant_n = drm_dp_has_quirk(&intel_dp->desc,
+ DP_DPCD_QUIRK_CONSTANT_N);
if (HAS_PCH_SPLIT(dev_priv) && !HAS_DDI(dev_priv) && port != PORT_A)
pipe_config->has_pch_encoder = true;
@@ -2064,7 +2064,7 @@ intel_dp_compute_config(struct intel_encoder *encoder,
adjusted_mode->crtc_clock,
pipe_config->port_clock,
&pipe_config->dp_m_n,
- reduce_m_n);
+ constant_n);
if (intel_connector->panel.downclock_mode != NULL &&
dev_priv->drrs.type == SEAMLESS_DRRS_SUPPORT) {
@@ -2074,7 +2074,7 @@ intel_dp_compute_config(struct intel_encoder *encoder,
intel_connector->panel.downclock_mode->clock,
pipe_config->port_clock,
&pipe_config->dp_m2_n2,
- reduce_m_n);
+ constant_n);
}
if (!HAS_DDI(dev_priv))
diff --git a/drivers/gpu/drm/i915/intel_dp_mst.c
b/drivers/gpu/drm/i915/intel_dp_mst.c
index 352e5216cc65..184023435b08 100644
--- a/drivers/gpu/drm/i915/intel_dp_mst.c
+++ b/drivers/gpu/drm/i915/intel_dp_mst.c
@@ -45,8 +45,8 @@ static bool intel_dp_mst_compute_config(struct intel_encoder
*encoder,
int lane_count, slots;
const struct drm_display_mode *adjusted_mode =
&pipe_config->base.adjusted_mode;
int mst_pbn;
- bool reduce_m_n = drm_dp_has_quirk(&intel_dp->desc,
- DP_DPCD_QUIRK_LIMITED_M_N);
+ bool constant_n = drm_dp_has_quirk(&intel_dp->desc,
+ DP_DPCD_QUIRK_CONSTANT_N);
if (adjusted_mode->flags & DRM_MODE_FLAG_DBLSCAN)
return false;
@@ -87,7 +87,7 @@ static bool intel_dp_mst_compute_config(struct intel_encoder
*encoder,
adjusted_mode->crtc_clock,
pipe_config->port_clock,
&pipe_config->dp_m_n,
- reduce_m_n);
+ constant_n);
pipe_config->dp_m_n.tu = slots;
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
index 05cc31b5db16..f59359e42428 100644
--- a/include/drm/drm_dp_helper.h
+++ b/include/drm/drm_dp_helper.h
@@ -1260,12 +1260,12 @@ int drm_dp_read_desc(struct drm_dp_aux *aux, struct
drm_dp_desc *desc,
*/
enum drm_dp_quirk {
/**
- * @DP_DPCD_QUIRK_LIMITED_M_N:
+ * @DP_DPCD_QUIRK_CONSTANT_N:
*
* The device requires main link attributes Mvid and Nvid to be limited
- * to 16 bits.
+ * to 16 bits. So will give a constant value (0x8000) for compatability.
*/
- DP_DPCD_QUIRK_LIMITED_M_N,
+ DP_DPCD_QUIRK_CONSTANT_N,
};
/**
--
2.7.4
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