[PATCH v4 14/16] drm: bridge: analogix/dp: try force hpd after plug in lookup failed

On Sun, Sep 06, 2015 at 11:59:08AM +0800, Yakir Yang wrote:

Hi Thierry,

? 09/03/2015 05:04 PM, Thierry Reding ??:

quoted

On Thu, Sep 03, 2015 at 12:27:47PM +0800, Yakir Yang wrote:

quoted

Hi Rob,

? 09/03/2015 04:17 AM, Rob Herring ??:

quoted

On Tue, Sep 1, 2015 at 1:14 AM, Yakir Yang [off-list ref] wrote:

quoted

Some edp screen do not have hpd signal, so we can't just return
failed when hpd plug in detect failed.

This is a property of the panel (or connector perhaps), so this
property should be located there. At least, it is a common issue and
not specific to this chip. We could have an HDMI connector and failed
to hook up HPD for example. A connector node is also where hpd-gpios
should be located instead (and are already defined by
../bindings/video/hdmi-connector.txt). Perhaps we need a eDP connector
binding, too.

Yep, I agree with your front point, it is a property of panel, not specific
to eDP controller, so this code should handle in connector logic.

From your description it sounds more like this is in fact a property of
the panel. Or maybe I should say "quirk". If the panel doesn't generate
the HPD signal, then that should be a property of the panel, not the
connector. The eDP specification mandates that connectors have a HPD
signal, though it allows the "HPD conductor in the connector cable" to
be omitted if not used by the source. I'd consider the cable to belong
to the panel rather than the connector, so absence of HPD, either
because the cable doesn't have the conductor or because the panel does
not generate the signal, should be a quirk of the panel.

That said you could have a panel that supports HPD connected via a cable
that doesn't transmit it, so this would be a per-board variant and hence
should be a device tree property rather than hard-coded in some panel
driver.

Conversely, if the panel isn't capable of generating an HPD signal, then
I don't think it would be appropriate to make it a DT property. It would
be better to hard-code it in the driver, lest someone forget to set the
property in DT and get stuck with a device that isn't operational.

Oh, you're right, if it's a cable quirk, then DT property would be okay, if
it
is a problem of panel, then maybe hard-code in driver would be better.

After look up for the document of panel "innolux,n116bge", I haven't see
any description of hot plug signal, and even not found in PIN ASSIGNMENT.
So I believe it's a panel problem, that's to say it should handle in panel
driver.

The datasheet that I have for that panel lists HPD as pin 17. Also I
used to have a setup with that panel and I distinctly remember hotplug
working just fine. Perhaps this is an issue with a specific variant of
the panel? Or perhaps this is indeed a problem with the cable that's
connecting the panel to the board. It could be one of those cases where
they left out the HPD conductor to save money.

Thierry
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