Commit 516c0f7c authored by Thierry Reding's avatar Thierry Reding
Browse files

drm/dp: Add DisplayPort link helpers 



Add a helper to probe a DP link (read out the supported DPCD revision,
maximum rate, link count and capabilities) as well as power up the DP
link and configure it accordingly.

Reviewed-by: default avatarAlex Deucher <alexander.deucher@amd.com>
Reviewed-by: default avatarJani Nikula <jani.nikula@intel.com>
Signed-off-by: default avatarThierry Reding <treding@nvidia.com>
---
Changes in v5:
- export helpers

Changes in v4:
- fix a couple of typos in comments as pointed out by Alex Deucher

Changes in v3:
- split into drm_dp_link_power_up() and drm_dp_link_configure()
- do not change sink state for DPCD versions earlier than 1.1
- sleep for 1-2 ms after setting local sink to D0 state
- read and write consecutive registers where possible
- read DPCD revision when link is probed
- remove duplicate kerneldoc
parent 8d4adc6a

drivers/gpu/drm/drm_dp_helper.c

+97 −0
Original line number Diff line number Diff line
@@ -472,3 +472,100 @@ 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() and drm_dp_link_configure() to power up and

 * 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 values[3];

	int err;



	memset(link, 0, sizeof(*link));



	err = drm_dp_dpcd_read(aux, DP_DPCD_REV, values, sizeof(values));

	if (err < 0)

		return err;



	link->revision = values[0];

	link->rate = drm_dp_bw_code_to_link_rate(values[1]);

	link->num_lanes = values[2] & DP_MAX_LANE_COUNT_MASK;



	if (values[2] & DP_ENHANCED_FRAME_CAP)

		link->capabilities |= DP_LINK_CAP_ENHANCED_FRAMING;



	return 0;

}

EXPORT_SYMBOL(drm_dp_link_probe);



/**

 * drm_dp_link_power_up() - power up 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;



	/* DP_SET_POWER register is only available on DPCD v1.1 and later */

	if (link->revision < 0x11)

		return 0;



	err = drm_dp_dpcd_readb(aux, DP_SET_POWER, &value);

	if (err < 0)

		return err;



	value &= ~DP_SET_POWER_MASK;

	value |= DP_SET_POWER_D0;



	err = drm_dp_dpcd_writeb(aux, DP_SET_POWER, value);

	if (err < 0)

		return err;



	/*

	 * According to the DP 1.1 specification, a "Sink Device must exit the

	 * power saving state within 1 ms" (Section 2.5.3.1, Table 5-52, "Sink

	 * Control Field" (register 0x600).

	 */

	usleep_range(1000, 2000);



	return 0;

}

EXPORT_SYMBOL(drm_dp_link_power_up);



/**

 * drm_dp_link_configure() - 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_configure(struct drm_dp_aux *aux, struct drm_dp_link *link)

{

	u8 values[2];

	int err;



	values[0] = drm_dp_link_rate_to_bw_code(link->rate);

	values[1] = link->num_lanes;



	if (link->capabilities & DP_LINK_CAP_ENHANCED_FRAMING)

		values[1] |= DP_LANE_COUNT_ENHANCED_FRAME_EN;



	err = drm_dp_dpcd_write(aux, DP_LINK_BW_SET, values, sizeof(values));

	if (err < 0)

		return err;



	return 0;

}

EXPORT_SYMBOL(drm_dp_link_configure);

include/drm/drm_dp_helper.h

+17 −0
Original line number Diff line number Diff line
@@ -291,6 +291,7 @@ 
#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)
@@ -480,4 +481,20 @@ static inline ssize_t drm_dp_dpcd_writeb(struct drm_dp_aux *aux, 
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 char revision;

	unsigned int rate;

	unsigned int num_lanes;

	unsigned long capabilities;

};



int drm_dp_link_probe(struct drm_dp_aux *aux, struct drm_dp_link *link);

int drm_dp_link_power_up(struct drm_dp_aux *aux, struct drm_dp_link *link);

int drm_dp_link_configure(struct drm_dp_aux *aux, struct drm_dp_link *link);



#endif /* _DRM_DP_HELPER_H_ */

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