According to the DisplayPort standard, LTTPRs have two operating
modes:
- non-transparent - it replies to DPCD LTTPR field specific AUX
requests, while passes through all other AUX requests
- transparent - it passes through all AUX requests.
Switching between this two modes is done by the DPTX by issuing
an AUX write to the DPCD PHY_REPEATER_MODE register.
Add a generic helper that allows switching between these modes.
Also add a generic wrapper for the helper that handles the explicit
disabling of non-transparent mode and its disable->enable sequence
mentioned in the DP Standard v2.0 section 3.6.6.1. Do this in order
to move this handling out of the vendor specific driver implementation
into the generic framework.
Tested-by: Johan Hovold <johan+linaro@kernel.org>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
---
drivers/gpu/drm/display/drm_dp_helper.c | 61 +++++++++++++++++++++++++++++++++
include/drm/display/drm_dp_helper.h | 2 ++
2 files changed, 63 insertions(+)
diff --git a/drivers/gpu/drm/display/drm_dp_helper.c b/drivers/gpu/drm/display/drm_dp_helper.c
index da3c8521a7fa7d3c9761377363cdd4b44ab1106e..0f665d9adf02cfd16f0c250eb7ae8fe0461f8fdd 100644
--- a/drivers/gpu/drm/display/drm_dp_helper.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c
@@ -2817,6 +2817,67 @@ int drm_dp_lttpr_max_link_rate(const u8 caps[DP_LTTPR_COMMON_CAP_SIZE])
}
EXPORT_SYMBOL(drm_dp_lttpr_max_link_rate);
+/**
+ * drm_dp_lttpr_set_transparent_mode - set the LTTPR in transparent mode
+ * @aux: DisplayPort AUX channel
+ * @enable: Enable or disable transparent mode
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_lttpr_set_transparent_mode(struct drm_dp_aux *aux, bool enable)
+{
+ u8 val = enable ? DP_PHY_REPEATER_MODE_TRANSPARENT :
+ DP_PHY_REPEATER_MODE_NON_TRANSPARENT;
+ int ret = drm_dp_dpcd_writeb(aux, DP_PHY_REPEATER_MODE, val);
+
+ if (ret < 0)
+ return ret;
+
+ return (ret == 1) ? 0 : -EIO;
+}
+EXPORT_SYMBOL(drm_dp_lttpr_set_transparent_mode);
+
+/**
+ * drm_dp_lttpr_init - init LTTPR transparency mode according to DP standard
+ *
+ * @aux: DisplayPort AUX channel
+ * @lttpr_count: Number of LTTPRs. Between 0 and 8, according to DP standard.
+ * Negative error code for any non-valid number.
+ * See drm_dp_lttpr_count().
+ *
+ * Returns 0 on success or a negative error code on failure.
+ */
+int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count)
+{
+ int ret;
+
+ if (!lttpr_count)
+ return 0;
+
+ /*
+ * See DP Standard v2.0 3.6.6.1 about the explicit disabling of
+ * non-transparent mode and the disable->enable non-transparent mode
+ * sequence.
+ */
+ ret = drm_dp_lttpr_set_transparent_mode(aux, true);
+ if (ret)
+ return ret;
+
+ if (lttpr_count < 0)
+ return -ENODEV;
+
+ /*
+ * Roll-back to tranparent mode if setting non-tranparent mode failed
+ */
+ if (drm_dp_lttpr_set_transparent_mode(aux, false)) {
+ drm_dp_lttpr_set_transparent_mode(aux, true);
+ return -EINVAL;
+ }
+
+ return 0;
+}
+EXPORT_SYMBOL(drm_dp_lttpr_init);
+
/**
* drm_dp_lttpr_max_lane_count - get the maximum lane count supported by all LTTPRs
* @caps: LTTPR common capabilities
diff --git a/include/drm/display/drm_dp_helper.h b/include/drm/display/drm_dp_helper.h
index 8f4054a560396a43750570a8c2e95624039ab8ad..3311df3b58255cf0620391d0948ccf6b569a8a34 100644
--- a/include/drm/display/drm_dp_helper.h
+++ b/include/drm/display/drm_dp_helper.h
@@ -630,6 +630,8 @@ int drm_dp_read_lttpr_phy_caps(struct drm_dp_aux *aux,
u8 caps[DP_LTTPR_PHY_CAP_SIZE]);
int drm_dp_lttpr_count(const u8 cap[DP_LTTPR_COMMON_CAP_SIZE]);
int drm_dp_lttpr_max_link_rate(const u8 caps[DP_LTTPR_COMMON_CAP_SIZE]);
+int drm_dp_lttpr_set_transparent_mode(struct drm_dp_aux *aux, bool enable);
+int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count);
int drm_dp_lttpr_max_lane_count(const u8 caps[DP_LTTPR_COMMON_CAP_SIZE]);
bool drm_dp_lttpr_voltage_swing_level_3_supported(const u8 caps[DP_LTTPR_PHY_CAP_SIZE]);
bool drm_dp_lttpr_pre_emphasis_level_3_supported(const u8 caps[DP_LTTPR_PHY_CAP_SIZE]);
--
2.34.1On Fri, Jan 03, 2025 at 02:58:15PM +0200, Abel Vesa wrote:
> According to the DisplayPort standard, LTTPRs have two operating
> modes:
> - non-transparent - it replies to DPCD LTTPR field specific AUX
> requests, while passes through all other AUX requests
> - transparent - it passes through all AUX requests.
>
> Switching between this two modes is done by the DPTX by issuing
> an AUX write to the DPCD PHY_REPEATER_MODE register.
>
> Add a generic helper that allows switching between these modes.
>
> Also add a generic wrapper for the helper that handles the explicit
> disabling of non-transparent mode and its disable->enable sequence
> mentioned in the DP Standard v2.0 section 3.6.6.1. Do this in order
> to move this handling out of the vendor specific driver implementation
> into the generic framework.
>
> Tested-by: Johan Hovold <johan+linaro@kernel.org>
> Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
> +/**
> + * drm_dp_lttpr_init - init LTTPR transparency mode according to DP standard
> + *
> + * @aux: DisplayPort AUX channel
> + * @lttpr_count: Number of LTTPRs. Between 0 and 8, according to DP standard.
> + * Negative error code for any non-valid number.
> + * See drm_dp_lttpr_count().
> + *
> + * Returns 0 on success or a negative error code on failure.
> + */
> +int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count)
> +{
> + int ret;
> +
> + if (!lttpr_count)
> + return 0;
> +
> + /*
> + * See DP Standard v2.0 3.6.6.1 about the explicit disabling of
> + * non-transparent mode and the disable->enable non-transparent mode
> + * sequence.
> + */
> + ret = drm_dp_lttpr_set_transparent_mode(aux, true);
> + if (ret)
> + return ret;
> +
> + if (lttpr_count < 0)
> + return -ENODEV;
> +
> + /*
> + * Roll-back to tranparent mode if setting non-tranparent mode failed
typo: transparent (2x)
> + */
I think this comment now needs to go inside the conditional, if you want
to keep it at all.
> + if (drm_dp_lttpr_set_transparent_mode(aux, false)) {
> + drm_dp_lttpr_set_transparent_mode(aux, true);
> + return -EINVAL;
> + }
> +
> + return 0;
> +}
> +EXPORT_SYMBOL(drm_dp_lttpr_init);
This looks much better to me now, so with the above addressed:
Reviewed-by: Johan Hovold <johan+linaro@kernel.org>
On 25-01-07 10:30:29, Johan Hovold wrote:
> On Fri, Jan 03, 2025 at 02:58:15PM +0200, Abel Vesa wrote:
> > According to the DisplayPort standard, LTTPRs have two operating
> > modes:
> > - non-transparent - it replies to DPCD LTTPR field specific AUX
> > requests, while passes through all other AUX requests
> > - transparent - it passes through all AUX requests.
> >
> > Switching between this two modes is done by the DPTX by issuing
> > an AUX write to the DPCD PHY_REPEATER_MODE register.
> >
> > Add a generic helper that allows switching between these modes.
> >
> > Also add a generic wrapper for the helper that handles the explicit
> > disabling of non-transparent mode and its disable->enable sequence
> > mentioned in the DP Standard v2.0 section 3.6.6.1. Do this in order
> > to move this handling out of the vendor specific driver implementation
> > into the generic framework.
> >
> > Tested-by: Johan Hovold <johan+linaro@kernel.org>
> > Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
>
> > +/**
> > + * drm_dp_lttpr_init - init LTTPR transparency mode according to DP standard
> > + *
> > + * @aux: DisplayPort AUX channel
> > + * @lttpr_count: Number of LTTPRs. Between 0 and 8, according to DP standard.
> > + * Negative error code for any non-valid number.
> > + * See drm_dp_lttpr_count().
> > + *
> > + * Returns 0 on success or a negative error code on failure.
> > + */
> > +int drm_dp_lttpr_init(struct drm_dp_aux *aux, int lttpr_count)
> > +{
> > + int ret;
> > +
> > + if (!lttpr_count)
> > + return 0;
> > +
> > + /*
> > + * See DP Standard v2.0 3.6.6.1 about the explicit disabling of
> > + * non-transparent mode and the disable->enable non-transparent mode
> > + * sequence.
> > + */
> > + ret = drm_dp_lttpr_set_transparent_mode(aux, true);
> > + if (ret)
> > + return ret;
> > +
> > + if (lttpr_count < 0)
> > + return -ENODEV;
> > +
> > + /*
> > + * Roll-back to tranparent mode if setting non-tranparent mode failed
>
> typo: transparent (2x)
Will fix.
>
> > + */
>
> I think this comment now needs to go inside the conditional, if you want
> to keep it at all.
Yes, will move it.
>
> > + if (drm_dp_lttpr_set_transparent_mode(aux, false)) {
> > + drm_dp_lttpr_set_transparent_mode(aux, true);
> > + return -EINVAL;
> > + }
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL(drm_dp_lttpr_init);
>
> This looks much better to me now, so with the above addressed:
>
> Reviewed-by: Johan Hovold <johan+linaro@kernel.org>
Thanks for reviewing!
Abel
On Fri, Jan 03, 2025 at 02:58:15PM +0200, Abel Vesa wrote: > According to the DisplayPort standard, LTTPRs have two operating > modes: > - non-transparent - it replies to DPCD LTTPR field specific AUX > requests, while passes through all other AUX requests > - transparent - it passes through all AUX requests. > > Switching between this two modes is done by the DPTX by issuing > an AUX write to the DPCD PHY_REPEATER_MODE register. > > Add a generic helper that allows switching between these modes. > > Also add a generic wrapper for the helper that handles the explicit > disabling of non-transparent mode and its disable->enable sequence > mentioned in the DP Standard v2.0 section 3.6.6.1. Do this in order > to move this handling out of the vendor specific driver implementation > into the generic framework. > > Tested-by: Johan Hovold <johan+linaro@kernel.org> > Signed-off-by: Abel Vesa <abel.vesa@linaro.org> > --- > drivers/gpu/drm/display/drm_dp_helper.c | 61 +++++++++++++++++++++++++++++++++ > include/drm/display/drm_dp_helper.h | 2 ++ > 2 files changed, 63 insertions(+) > Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org> -- With best wishes Dmitry
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