From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jani Nikula <jani.nikula@intel.com>
Subject: Re: [PATCH] drm/i915: support address only i2c-over-aux
	transactions
Date: Tue, 08 Apr 2014 09:58:43 +0300
Message-ID: <87bnwc9ujg.fsf@intel.com>
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To: Daniel Vetter <daniel@ffwll.ch>, Alex Deucher <alexdeucher@gmail.com>
Cc: Intel Graphics Development <intel-gfx@lists.freedesktop.org>, Maling list - DRI developers <dri-devel@lists.freedesktop.org>
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On Mon, 07 Apr 2014, Daniel Vetter <daniel@ffwll.ch> wrote:
> On Mon, Apr 7, 2014 at 4:35 PM, Alex Deucher <alexdeucher@gmail.com> wrote:
>> On Mon, Apr 7, 2014 at 5:37 AM, Jani Nikula <jani.nikula@intel.com> wrote:
>>> To support bare address requests used by the drm dp helpers.
>>>
>>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>>>
>>> ---
>>>
>>> Hi Alex, similar to Thierry's patch for i915.
>>>
>>
>> Looks good to me.
>>
>> Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
>>
>> Do you want me to add this to the patch set?
>
> Afaict we've done an unconditional msg_bytes = send_bytes + 4; in the
> i915 driver before the conversion to the dp aux helper, which is why
> I've slapped an r-b onto your patch without asking for a i915
> adjustement. Otoh we have a pile of bugs for dp dongles still. Imo my
> preferred approach would be to get the helper + radeon stuff in and
> then hawk the i915 patch to a bunch of bug reporter and see whether it
> sticks. Ofc if we already know that we need it it would be best to
> merge it in one pull together with all your other patches.
>
> Jani?

Before the conversion to dp aux helpers there was a switch case [1] that
ended up in msg_bytes = 3 for address only start/stop messages
(MODE_I2C_START or MODE_I2C_STOP bit set [2]). With Alex's series in,
but without my patch, we'd send the four byte header but with 0 - 1 =
0xff in txbuf[3]. I'm pretty sure breakage would follow.

Thus I'd like to have my patch in before the dp aux helpers use
msg->size == 0 for address only messages.

Daniel, convinced yet?

BR,
Jani.


[1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/i915/intel_dp.c?id=v3.14#n654

[2] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/drivers/gpu/drm/drm_dp_helper.c?id=v3.14#n59


> -Daniel
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
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-- 
Jani Nikula, Intel Open Source Technology Center