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Date: Fri, 22 Mar 2019 12:01:07 -0700 From: Andrey Smirnov <andrew.smirnov@...il.com> To: Tomi Valkeinen <tomi.valkeinen@...com> Cc: dri-devel@...ts.freedesktop.org, Archit Taneja <architt@...eaurora.org>, Andrzej Hajda <a.hajda@...sung.com>, Laurent Pinchart <Laurent.pinchart@...asonboard.com>, Andrey Gusakov <andrey.gusakov@...entembedded.com>, Philipp Zabel <p.zabel@...gutronix.de>, Chris Healy <cphealy@...il.com>, Lucas Stach <l.stach@...gutronix.de>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH v2 08/15] drm/bridge: tc358767: Increase AUX transfer length limit On Fri, Mar 22, 2019 at 6:14 AM Tomi Valkeinen <tomi.valkeinen@...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
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