linux-kernel - [PATCH] drm/bridge: ti-sn65dsi86: Implement wait_hpd

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Message-Id: <20230408082014.235425-1-nikita@trvn.ru>
Date:   Sat,  8 Apr 2023 13:20:14 +0500
From:   Nikita Travkin <nikita@...n.ru>
To:     andrzej.hajda@...el.com, neil.armstrong@...aro.org,
        rfoss@...nel.org
Cc:     airlied@...il.com, daniel@...ll.ch, dianders@...omium.org,
        Laurent.pinchart@...asonboard.com, jonas@...boo.se,
        jernej.skrabec@...il.com, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Nikita Travkin <nikita@...n.ru>
Subject: [PATCH] drm/bridge: ti-sn65dsi86: Implement wait_hpd_asserted

This bridge doesn't actually implement HPD due to it being way too slow
but instead expects the panel driver to wait enough to assume HPD is
asserted. However some panels (such as the generic 'edp-panel') expect
the bridge to deal with the delay and pass maximum delay to the aux
instead.

In order to support such panels, add a dummy implementation of wait
that would just sleep the maximum delay and assume no failure has
happened.

Signed-off-by: Nikita Travkin <nikita@...n.ru>
---
This was suggested in [1] to make sure DT users can be semantically
correct (not adding no-hpd when the line is actually there) while
still using a hard delay to be faster than waiting the long debounce
time.

[1] - https://lore.kernel.org/all/CAD=FV=VR7sKsquE25eF7joc7gPApu-vqwduZzjE=wFCoXjMYnQ@mail.gmail.com/
---
 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 7a748785c545..260cad1fd1da 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -618,6 +618,24 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
 	return len;
 }
 
+static int ti_sn_aux_wait_hpd_asserted(struct drm_dp_aux *aux, unsigned long wait_us)
+{
+	/*
+	 * The HPD in this chip is a bit useless (See comment in
+	 * ti_sn65dsi86_enable_comms) so if our driver is expected to wait
+	 * for HPD, we just assume it's asserted after the wait_us delay.
+	 *
+	 * In case we are asked to wait forever (wait_us=0) take conservative
+	 * 500ms delay.
+	 */
+	if (wait_us == 0)
+		wait_us = 500000;
+
+	usleep_range(wait_us, wait_us + 1000);
+
+	return 0;
+}
+
 static int ti_sn_aux_probe(struct auxiliary_device *adev,
 			   const struct auxiliary_device_id *id)
 {
@@ -627,6 +645,7 @@ static int ti_sn_aux_probe(struct auxiliary_device *adev,
 	pdata->aux.name = "ti-sn65dsi86-aux";
 	pdata->aux.dev = &adev->dev;
 	pdata->aux.transfer = ti_sn_aux_transfer;
+	pdata->aux.wait_hpd_asserted = ti_sn_aux_wait_hpd_asserted;
 	drm_dp_aux_init(&pdata->aux);
 
 	ret = devm_of_dp_aux_populate_ep_devices(&pdata->aux);
-- 
2.39.2