linux-kernel - [PATCH v3 2/4] drm/bridge: ti-sn65dsi86: Make polling a busy loop

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Message-Id: <20201102181144.3469197-3-swboyd@chromium.org>
Date:   Mon,  2 Nov 2020 10:11:42 -0800
From:   Stephen Boyd <swboyd@...omium.org>
To:     Andrzej Hajda <a.hajda@...sung.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        Sam Ravnborg <sam@...nborg.org>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Douglas Anderson <dianders@...omium.org>,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Jonas Karlman <jonas@...boo.se>,
        Jernej Skrabec <jernej.skrabec@...l.net>,
        Sean Paul <seanpaul@...omium.org>
Subject: [PATCH v3 2/4] drm/bridge: ti-sn65dsi86: Make polling a busy loop

There's no reason we need to wait here to poll a register over i2c. The
i2c bus is inherently slow and delays are practically part of the
protocol because we have to wait for the device to respond to any
request for a register. Let's rely on the sleeping of the i2c controller
instead of adding any sort of delay here in the bridge driver.

Reviewed-by: Douglas Anderson <dianders@...omium.org>
Cc: Laurent Pinchart <Laurent.pinchart@...asonboard.com>
Cc: Jonas Karlman <jonas@...boo.se>
Cc: Jernej Skrabec <jernej.skrabec@...l.net>
Cc: Sean Paul <seanpaul@...omium.org>
Acked-by: Sam Ravnborg <sam@...nborg.org>
Signed-off-by: Stephen Boyd <swboyd@...omium.org>
---
 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 87726b9e446f..8276fa50138f 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -881,9 +881,9 @@ static ssize_t ti_sn_aux_transfer(struct drm_dp_aux *aux,
 
 	regmap_write(pdata->regmap, SN_AUX_CMD_REG, request_val | AUX_CMD_SEND);
 
+	/* Zero delay loop because i2c transactions are slow already */
 	ret = regmap_read_poll_timeout(pdata->regmap, SN_AUX_CMD_REG, val,
-				       !(val & AUX_CMD_SEND), 200,
-				       50 * 1000);
+				       !(val & AUX_CMD_SEND), 0, 50 * 1000);
 	if (ret)
 		return ret;
 
-- 
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