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.
v2: Rebased on top of drm_dp_helper docbook changes. Also this version add EAGAIN documentation and as suggested by Jani it inserts a comment at drm_dp_i2c_do_msg explaining EAGAIN timeout is already handled at i2c level.
Cc: Jani Nikula jani.nikula@intel.com Cc: Dave Airlie airlied@redhat.com Signed-off-by: Rodrigo Vivi rodrigo.vivi@intel.com Tested-by: Daniel Stone daniels@collabora.com Signed-off-by: Rodrigo Vivi rodrigo.vivi@intel.com --- drivers/gpu/drm/drm_dp_helper.c | 10 ++++++++++ include/drm/drm_dp_helper.h | 4 ++++ 2 files changed, 14 insertions(+)
diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c index 9535c5b..2e26097 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;
@@ -547,6 +552,11 @@ static int drm_dp_i2c_do_msg(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg) ret = aux->transfer(aux, msg); mutex_unlock(&aux->hw_mutex); if (ret < 0) { + + /* + * -EAGAIN retries are handled by i2c layer with + * timeouts for repeated -EAGAINs + */ if (ret == -EBUSY) continue;
diff --git a/include/drm/drm_dp_helper.h b/include/drm/drm_dp_helper.h index ed7dbdc..518fc1b 100644 --- a/include/drm/drm_dp_helper.h +++ b/include/drm/drm_dp_helper.h @@ -758,6 +758,10 @@ struct drm_dp_aux { * to check for failure. * - -EBUSY: When BUSY helpers will attempt retries before propagating * this error. + * - -EAGAIN: DPCD helper will attempt immediatelly retries before + * propagating this error. i2c helper will only propagate directly + * since i2c layer already perform retries with timeouts for repeated + * -EAGAINs. * * Note that the aux helper code assumes that the .transfer() function * only modifies the reply field of the drm_dp_aux_msg structure. The