| Message ID | 20190322032901.12045-9-andrew.smirnov@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | tc358767 driver improvements | expand |
On Fri, Mar 22, 2019 at 6:14 AM Tomi Valkeinen <tomi.valkeinen@ti.com> wrote: > > On 22/03/2019 05:28, Andrey Smirnov wrote: > > According to the datasheet tc358767 can transfer up to 16 bytes via > > its AUX channel, so the artificial limit of 8 apperas to be too > > low. However only up to 15-bytes seem to be actually supported and > > trying to use 16-byte transfers results in transfers failing > > sporadically (with bogus status in case of I2C transfers), so limit it > > to 15. > > 16 is the limit from the DP spec. I agree, 8 looks odd. > > 15 looks odd too, so I think it warrants a comment there in the code. > Crap, was going to add that, but forgot. Will do in v2. > Does 15 byte transfers ever work? Or mostly works but sometimes fails? > 15 bytes transfers work every time (at least to extent I tested it). For 16 byte transfers it depends on the transfer type. AUX transfers work for a while but then fail (as tested by dd'ing AUX chardev). I2C transfers work intermittently and when they fail return completely bogus status. Thanks, Andrey Smirnov
diff --git a/drivers/gpu/drm/bridge/tc358767.c b/drivers/gpu/drm/bridge/tc358767.c index 21374565585d..8adaac5ca271 100644 --- a/drivers/gpu/drm/bridge/tc358767.c +++ b/drivers/gpu/drm/bridge/tc358767.c @@ -358,7 +358,7 @@ static ssize_t tc_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg) { struct tc_data *tc = aux_to_tc(aux); - size_t size = min_t(size_t, 8, msg->size); + size_t size = min_t(size_t, DP_AUX_MAX_PAYLOAD_BYTES - 1, msg->size); u8 request = msg->request & ~DP_AUX_I2C_MOT; int ret;
According to the datasheet tc358767 can transfer up to 16 bytes via its AUX channel, so the artificial limit of 8 apperas to be too low. However only up to 15-bytes seem to be actually supported and trying to use 16-byte transfers results in transfers failing sporadically (with bogus status in case of I2C transfers), so limit it to 15. Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com> Cc: Archit Taneja <architt@codeaurora.org> Cc: Andrzej Hajda <a.hajda@samsung.com> Cc: Laurent Pinchart <Laurent.pinchart@ideasonboard.com> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com> Cc: Andrey Gusakov <andrey.gusakov@cogentembedded.com> Cc: Philipp Zabel <p.zabel@pengutronix.de> Cc: Chris Healy <cphealy@gmail.com> Cc: Lucas Stach <l.stach@pengutronix.de> Cc: dri-devel@lists.freedesktop.org Cc: linux-kernel@vger.kernel.org --- drivers/gpu/drm/bridge/tc358767.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)