On Fri, 2020-09-04 at 14:53 +0300, Ville Syrjala wrote:
> From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
>
> Add helpers to get the TMDS clock limits for HDMI/DVI downstream
> facing ports.
>
> Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_dp_helper.c | 116 ++++++++++++++++++++++++++++++++
> include/drm/drm_dp_helper.h | 6 ++
> 2 files changed, 122 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c
> b/drivers/gpu/drm/drm_dp_helper.c
> index 822a30e609ef..f567428f2aef 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -643,6 +643,114 @@ int drm_dp_downstream_max_dotclock(const u8
> dpcd[DP_RECEIVER_CAP_SIZE],
> }
> EXPORT_SYMBOL(drm_dp_downstream_max_dotclock);
>
> +/**
> + * drm_dp_downstream_max_tmds_clock() - extract downstream facing port max
> TMDS clock
> + * @dpcd: DisplayPort configuration data
> + * @port_cap: port capabilities
> + * @edid: EDID
> + *
> + * Returns HDMI/DVI downstream facing port max TMDS clock in kHz on
> success,
> + * or 0 if max TMDS clock not defined
> + */
> +int drm_dp_downstream_max_tmds_clock(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> + const u8 port_cap[4],
> + const struct edid *edid)
> +{
> + if (!drm_dp_is_branch(dpcd))
> + return 0;
> +
> + if (dpcd[DP_DPCD_REV] < 0x11) {
> + switch (dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> DP_DWN_STRM_PORT_TYPE_MASK) {
> + case DP_DWN_STRM_PORT_TYPE_TMDS:
> + return 165000;
> + default:
> + return 0;
> + }
> + }
> +
> + switch (port_cap[0] & DP_DS_PORT_TYPE_MASK) {
> + case DP_DS_PORT_TYPE_DP_DUALMODE:
> + if (is_edid_digital_input_dp(edid))
> + return 0;
> + /*
> + * It's left up to the driver to check the
> + * DP dual mode adapter's max TMDS clock.
> + *
> + * Unfortunatley it looks like branch devices
> + * may not fordward that the DP dual mode i2c
> + * access so we just usually get i2c nak :(
> + */
> + fallthrough;
> + case DP_DS_PORT_TYPE_HDMI:
> + /*
> + * We should perhaps assume 165 MHz when detailed cap
> + * info is not available. But looks like many typical
> + * branch devices fall into that category and so we'd
> + * probably end up with users complaining that they can't
> + * get high resolution modes with their favorite dongle.
> + *
> + * So let's limit to 300 MHz instead since DPCD 1.4
> + * HDMI 2.0 DFPs are required to have the detailed cap
> + * info. So it's more likely we're dealing with a HDMI 1.4
> + * compatible* device here.
Forgot to mention - not directly related to this series, there's some hidden
i2c bits that I think can also be probed for this sort of information on
passive adapters, I know amdgpu actually supports this. I wonder how many of
them also apply to older active adapters...
> + */
> + if ((dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> DP_DETAILED_CAP_INFO_AVAILABLE) == 0)
> + return 300000;
> + return port_cap[1] * 2500;
> + case DP_DS_PORT_TYPE_DVI:
> + if ((dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> DP_DETAILED_CAP_INFO_AVAILABLE) == 0)
> + return 165000;
> + /* FIXME what to do about DVI dual link? */
> + return port_cap[1] * 2500;
> + default:
> + return 0;
> + }
> +}
> +EXPORT_SYMBOL(drm_dp_downstream_max_tmds_clock);
> +
> +/**
> + * drm_dp_downstream_min_tmds_clock() - extract downstream facing port min
> TMDS clock
> + * @dpcd: DisplayPort configuration data
> + * @port_cap: port capabilities
> + * @edid: EDID
> + *
> + * Returns HDMI/DVI downstream facing port min TMDS clock in kHz on
> success,
> + * or 0 if max TMDS clock not defined
> + */
> +int drm_dp_downstream_min_tmds_clock(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> + const u8 port_cap[4],
> + const struct edid *edid)
> +{
> + if (!drm_dp_is_branch(dpcd))
> + return 0;
> +
> + if (dpcd[DP_DPCD_REV] < 0x11) {
> + switch (dpcd[DP_DOWNSTREAMPORT_PRESENT] &
> DP_DWN_STRM_PORT_TYPE_MASK) {
> + case DP_DWN_STRM_PORT_TYPE_TMDS:
> + return 25000;
> + default:
> + return 0;
> + }
> + }
> +
> + switch (port_cap[0] & DP_DS_PORT_TYPE_MASK) {
> + case DP_DS_PORT_TYPE_DP_DUALMODE:
> + if (is_edid_digital_input_dp(edid))
> + return 0;
> + fallthrough;
> + case DP_DS_PORT_TYPE_DVI:
> + case DP_DS_PORT_TYPE_HDMI:
> + /*
> + * Unclear whether the protocol converter could
> + * utilize pixel replication. Assume it won't.
> + */
> + return 25000;
> + default:
> + return 0;
> + }
> +}
> +EXPORT_SYMBOL(drm_dp_downstream_min_tmds_clock);
> +
> /**
> * drm_dp_downstream_max_bpc() - extract downstream facing port max
> * bits per component
> @@ -788,6 +896,14 @@ void drm_dp_downstream_debug(struct seq_file *m,
> if (clk > 0)
> seq_printf(m, "\t\tMax dot clock: %d kHz\n", clk);
>
> + clk = drm_dp_downstream_max_tmds_clock(dpcd, port_cap, edid);
> + if (clk > 0)
> + seq_printf(m, "\t\tMax TMDS clock: %d kHz\n", clk);
> +
> + clk = drm_dp_downstream_min_tmds_clock(dpcd, port_cap, edid);
> + if (clk > 0)
> + seq_printf(m, "\t\tMin TMDS clock: %d kHz\n", clk);
> +
> bpc = drm_dp_downstream_max_bpc(dpcd, port_cap, edid);
>
> if (bpc > 0)
> diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h
> index 19bc04207788..6812a3e0de8d 100644
> --- a/include/drm/drm_dp_helper.h
> +++ b/include/drm/drm_dp_helper.h
> @@ -1645,6 +1645,12 @@ bool drm_dp_downstream_is_tmds(const u8
> dpcd[DP_RECEIVER_CAP_SIZE],
> const struct edid *edid);
> int drm_dp_downstream_max_dotclock(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> const u8 port_cap[4]);
> +int drm_dp_downstream_max_tmds_clock(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> + const u8 port_cap[4],
> + const struct edid *edid);
> +int drm_dp_downstream_min_tmds_clock(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> + const u8 port_cap[4],
> + const struct edid *edid);
> int drm_dp_downstream_max_bpc(const u8 dpcd[DP_RECEIVER_CAP_SIZE],
> const u8 port_cap[4],
> const struct edid *edid);
--
Cheers,
Lyude Paul (she/her)
Software Engineer at Red Hat
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