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

From: Andrey Smirnov
Date: Fri Mar 22 2019 - 15:01:23 EST

On Fri, Mar 22, 2019 at 6:14 AM Tomi Valkeinen <tomi.valkeinen@xxxxxx> 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.

Andrey Smirnov