[PATCH 1/8] drm: Introduce EAGAIN handling for immediatelly aux retries

[Rodrigo Vivi]

The goal here is to offload aux retries handling from the
drivers to drm.

However there are 2 differents cases for retry:
1. Immediately retry - Hardware already took care of needed timeouts
   	       	       before answering that a retry is possible.
2. Busy - Wait some time and retry.

This driver introduce the support for EAGAIN that can handle the
first case and a following patch will introduce EBUSY waits,
after all drivers counting on immediately retries are changed.

Cc: Dave Airlie <airlied at redhat.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi at intel.com>
---
 drivers/gpu/drm/drm_dp_helper.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
index 9535c5b..ee7c955 100644
--- a/drivers/gpu/drm/drm_dp_helper.c
+++ b/drivers/gpu/drm/drm_dp_helper.c
@@ -198,6 +198,11 @@ static int drm_dp_dpcd_access(struct drm_dp_aux *aux, u8 request,
 		err = aux->transfer(aux, &msg);
 		mutex_unlock(&aux->hw_mutex);
 		if (err < 0) {
+			/* Immediately retry */
+			if (err == -EAGAIN)
+				continue;
+
+			/* FIXME: On BUSY we could wait before retrying */
 			if (err == -EBUSY)
 				continue;
 
-- 
2.4.3