On Tue, 17 Dec 2013, Thierry Reding <thierry.reding@xxxxxxxxx> 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@xxxxxxxxxx>
> ---
> 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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> http://lists.freedesktop.org/mailman/listinfo/dri-devel
--
Jani Nikula, Intel Open Source Technology Center
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