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Subject: Re: [PATCH 3/3 v3] drm: bridge/dw-hdmi: Move edid reading to
 .detect() callback
To: Russell King - ARM Linux <linux@armlinux.org.uk>,
        Jose Abreu <Jose.Abreu@synopsys.com>
References: <cover.1470306826.git.joabreu@synopsys.com>
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 <20160804104738.GR1041@n2100.armlinux.org.uk> <57A349E8.5040400@synopsys.com>
 <20160804143102.GU1041@n2100.armlinux.org.uk>
CC: <dri-devel@lists.freedesktop.org>,
        Carlos Palminha <CARLOS.PALMINHA@synopsys.com>,
        Archit Taneja <architt@codeaurora.org>,
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From: Jose Abreu <Jose.Abreu@synopsys.com>
Message-ID: <57A357D1.1070900@synopsys.com>
Date: Thu, 4 Aug 2016 15:57:21 +0100
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Hi Russell,


On 04-08-2016 15:31, Russell King - ARM Linux wrote:
> On Thu, Aug 04, 2016 at 02:58:00PM +0100, Jose Abreu wrote:
>> Hi Russell,
>>
>> I am not sure if this is a bug in DRM or a bad implementation of
>> dw-hdmi. I've seen at least two more drivers that do the edid
>> reading at the .detect() callback: nouveau and gma500. This is
>> noticeable if while sending video the edid changes like in a
>> compliance environment. In the environment that I tested I was
>> sending video and swapped an edid that had support for AI packets
>> to another one without support and I noticed that although the
>> hotplug is generated the edid was not being updated.
> The path should be:
>
> - HPD interrupt
> - drm_helper_hpd_irq_event()
>   - generates uevent to userspace
>   - output_poll_changed() called
>     - drm_fb_helper_hotplug_event()
>       - drm_fb_helper_probe_connector_modes()
>         - connector->fill_modes()
>           - drm_helper_probe_single_connector_modes()
>             - connector_funcs->get_modes()
>
> Now, if we don't have fbdev emulation, then things won't get much
> fruther than output_poll_changed(), and the responsibility for
> reading the EDID falls onto userspace.  However, as soon as userspace
> or the kernel reads the new EDID, that is when any changes in it
> should become visible.
>
> Of course, that should occur in a timely fashion.
>

Hmm, I am not debugging it right now but I remember that
drm_fb_helper_probe_connector_modes() was not being called at the
time I set the new EDID but only after I stopped sending video (I
was using modetest).


Best regards,
Jose Miguel Abreu