[v2,08/15] drm/bridge: tc358767: Increase AUX transfer length limit

Submitted by Andrey Smirnov on March 22, 2019, 3:28 a.m.

Details

Message ID 20190322032901.12045-9-andrew.smirnov@gmail.com
State Accepted
Commit e0655feaec62d5139b6b13a7b1bbb1ab8f1c2d83
Headers show
Series "tc358767 driver improvements" ( rev: 2 ) in DRI devel

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Commit Message

Andrey Smirnov March 22, 2019, 3:28 a.m.
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(-)

Patch hide | download patch | download mbox

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;
 

Comments

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