On Sun, Sep 06, 2015 at 11:59:08AM +0800, Yakir Yang wrote: > Hi Thierry, > > 在 09/03/2015 05:04 PM, Thierry Reding 写道: > >On Thu, Sep 03, 2015 at 12:27:47PM +0800, Yakir Yang wrote: > >>Hi Rob, > >> > >>在 09/03/2015 04:17 AM, Rob Herring 写道: > >>>On Tue, Sep 1, 2015 at 1:14 AM, Yakir Yang <ykk@xxxxxxxxxxxxxx> wrote: > >>>>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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