drm/nouveau/i2c/gk110-: disable hw-initiated dpcd reads

RM does this around transactions, and it seemed to help while debugging
AUXCH issues on GA102.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drm/nouveau/i2c/g94-: increase NV_PMGR_DP_AUXCTL_TRANSACTREQ timeout

Tegra TRM says worst-case reply time is 1216us, and this should fix some
spurious timeouts that have been popping up.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drm/nouveau/i2c/gf119-: add support for address-only transactions

Since switching the I2C-over-AUX helpers, there have been regressions on
some display combinations due to us not having support for "address only"
transactions.

This commits enables support for them for GF119 and newer.

Earlier GPUs have been reverted to a custom I2C-over-AUX algorithm.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drm/nouveau/i2c/g94-: return REPLY_M value on reads

This value represents the actual number of bytes recieved on the AUX
channel as the result of a read transaction.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drm/nouveau/i2c: modify aux interface to return length actually transferred

Apparently sinks are allows to respond with ACK even if they didn't
fully complete a transaction... It seems like a missed opportunity
for DEFER to me, but what do I know :)

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drm/nouveau/i2c/aux/g94-: retry transactions after hw reports an error

This fixes (works around?) link training failures seen on (at least)
the Lenovo P50's internal panel.

It's also an important fix on the same system for MST support on the
dock. Sometimes, right after receiving an IRQ from the sink, there's
an error bit (SINKSTAT_ERR) set in the DPAUX registers before we've
even attempted a transaction.

v2. Fixed regression on passive DP->DVI adapters.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drm/nouveau/i2c: transition pad/ports away from being based on nvkm_object

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>