From 19a93f042fc241ecdf98543cedfe7c171f8cdf53 Mon Sep 17 00:00:00 2001 From: Dave Airlie Date: Wed, 26 Nov 2014 13:13:09 +1000 Subject: [PATCH] drm/dp: retry AUX transactions 32 times (v1.1) At least on two MST devices I've tested with, when they are link training downstream, they are totally unable to handle aux ch msgs, so they defer like nuts. I tried 16, it wasn't enough, 32 seems better. This fixes one Dell 4k monitor and one of the MST hubs. v1.1: fixup comment (Tom). Acked-by: Alex Deucher Cc: stable@vger.kernel.org Signed-off-by: Dave Airlie --- drivers/gpu/drm/drm_dp_helper.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 959e2074b0d4..79968e39c8d0 100644 --- a/drivers/gpu/drm/drm_dp_helper.c +++ b/drivers/gpu/drm/drm_dp_helper.c @@ -186,10 +186,11 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request, /* * The specification doesn't give any recommendation on how often to - * retry native transactions, so retry 7 times like for I2C-over-AUX - * transactions. + * retry native transactions. We used to retry 7 times like for + * aux i2c transactions but real world devices this wasn't + * sufficient, bump to 32 which makes Dell 4k monitors happier. */ - for (retry = 0; retry < 7; retry++) { + for (retry = 0; retry < 32; retry++) { mutex_lock(&aux->hw_mutex); err = aux->transfer(aux, &msg); -- 2.20.1