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

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Date:   Fri, 22 Mar 2019 15:14:41 +0200
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Andrey Smirnov <andrew.smirnov@...il.com>,
        <dri-devel@...ts.freedesktop.org>
CC:     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@...r.kernel.org>
Subject: Re: [PATCH v2 08/15] drm/bridge: tc358767: Increase AUX transfer
 length limit

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.

Does 15 byte transfers ever work? Or mostly works but sometimes fails?

 Tomi

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