On Tue, 17 Dec 2013, Thierry Reding thierry.reding@gmail.com wrote:
Add a helper to probe a DP link (reading out the maximum rate, link count and capabilities) as well as configuring it accordingly.
Signed-off-by: Thierry Reding treding@nvidia.com
drivers/gpu/drm/drm_dp_helper.c | 77 +++++++++++++++++++++++++++++++++++++++++ include/drm/drm_dp_helper.h | 30 ++++++++++++++++ 2 files changed, 107 insertions(+)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 8111b8e5a8bc..01a8173c6e83 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -478,3 +478,80 @@ int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux, DP_LINK_STATUS_SIZE); } EXPORT_SYMBOL(drm_dp_dpcd_read_link_status);
+/**
- drm_dp_link_probe() - probe a DisplayPort link for capabilities
- @aux: DisplayPort AUX channel
- @link: pointer to structure in which to return link capabilities
- The structure filled in by this function can usually be passed directly
- into drm_dp_link_power_up() configure the link based on the link's
- capabilities.
- Returns 0 on success or a negative error code on failure.
- */
+int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link) +{
- u8 value;
- int err;
- memset(link, 0, sizeof(*link));
- err = drm_dp_dpcd_readb(aux, DP_MAX_LINK_RATE, &value);
- if (err < 0)
return err;- link->rate = drm_dp_bw_code_to_link_rate(value);
- err = drm_dp_dpcd_readb(aux, DP_MAX_LANE_COUNT, &value);
- if (err < 0)
return err;- link->num_lanes = value & DP_MAX_LANE_COUNT_MASK;
- if (value & DP_ENHANCED_FRAME_CAP)
link->capabilities |= DP_LINK_CAP_ENHANCED_FRAMING;- return 0;
+}
Okay, I'm biased due to the i915 implementation, but I think it's better to read the first 16 bytes of DPCD in one block, cache that, and provide accessors to the information. Keep the DPCD reads and writes to a minimum.
+/**
- drm_dp_link_power_up() - power up and configure a DisplayPort link
- @aux: DisplayPort AUX channel
- @link: pointer to a structure containing the link configuration
- Returns 0 on success or a negative error code on failure.
- */
+int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link) +{
- u8 value;
- int err;
- err = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value);
If this is turning on the sink, we'll need to give the sink some time to wake up, and retry, per the DP spec.
Maybe I'd leave setting DP_SET_POWER up to the drivers altogether, at least for now. (Again, I'm biased, and this would make it easier for i915 to adopt this stuff. ;)
BR, Jani.
- if (err < 0)
return err;- value &= ~DP_SET_POWER_MASK;
- value |= DP_SET_POWER_D0;
- err = drm_dp_dpcd_writeb(aux, value, DP_SET_POWER);
- if (err < 0)
return err;- value = drm_dp_link_rate_to_bw_code(link->rate);
- err = drm_dp_dpcd_writeb(aux, value, DP_LINK_BW_SET);
- if (err < 0)
return err;- value = link->num_lanes;
- if (link->capabilities & DP_LINK_CAP_ENHANCED_FRAMING)
value |= DP_LANE_COUNT_ENHANCED_FRAME_EN;- err = drm_dp_dpcd_writeb(aux, value, DP_LANE_COUNT_SET);
- if (err < 0)
return err;
IMO you should always combine DPCD reads and writes as much as possible. DP_LINK_BW_SET and DP_LANE_COUNT_SET are back to back.
- return 0;
+} diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h index 38cbaef05005..bad9ee11a2e2 100644 --- a/include/drm/drm_dp_helper.h +++ b/include/drm/drm_dp_helper.h @@ -290,6 +290,7 @@ #define DP_SET_POWER 0x600 # define DP_SET_POWER_D0 0x1 # define DP_SET_POWER_D3 0x2 +# define DP_SET_POWER_MASK 0x3
#define DP_PSR_ERROR_STATUS 0x2006 /* XXX 1.2? */ # define DP_PSR_LINK_CRC_ERROR (1 << 0) @@ -464,4 +465,33 @@ static inline ssize_t drm_dp_dpcd_writeb(struct drm_dp_aux *aux, u8 value, int drm_dp_dpcd_read_link_status(struct drm_dp_aux *aux, u8 status[DP_LINK_STATUS_SIZE]);
+/*
- DisplayPort link
- */
+#define DP_LINK_CAP_ENHANCED_FRAMING (1 << 0)
+struct drm_dp_link {
- unsigned int rate;
- unsigned int num_lanes;
- unsigned long capabilities;
+};
+/**
- drm_dp_link_probe() - probe link properties and capabilities
- @aux: DisplayPort AUX channel
- @link: DisplayPort link
- Returns 0 on success or a negative error code on failure.
- */
+int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link);
+/**
- drm_dp_link_power_up() - power up a link
- @aux: DisplayPort AUX channel
- @link: DisplayPort link
- Returns 0 on success or a negative error code on failure.
- */
+int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link);
#endif /* _DRM_DP_HELPER_H_ */
1.8.4.2
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