lkml.org 
[lkml]   [2021]   [Sep]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v3 6/6] drm/ingenic: Attach bridge chain to encoders
Hi Nikolaus,

Le jeu., sept. 23 2021 at 13:41:28 +0200, H. Nikolaus Schaller
<hns@goldelico.com> a écrit :
> Hi Laurent,
>
>> Am 23.09.2021 um 12:03 schrieb Laurent Pinchart
>> <laurent.pinchart@ideasonboard.com>:
>>
>> Hi Nikolaus,
>>
>> On Thu, Sep 23, 2021 at 11:55:56AM +0200, H. Nikolaus Schaller
>> wrote:
>>>> Am 23.09.2021 um 11:27 schrieb Laurent Pinchart:
>>>> On Thu, Sep 23, 2021 at 11:19:23AM +0200, H. Nikolaus Schaller
>>>> wrote:
>>>>>
>>>>>>>> + ret = drm_bridge_attach(encoder, &ib->bridge, NULL,
>>>>>>>> + DRM_BRIDGE_ATTACH_NO_CONNECTOR);
>>>>>>>
>>>>>>> DRM_BRIDGE_ATTACH_NO_CONNECTOR makes it fundamentally
>>>>>>> incompatible
>>>>>>> with synopsys/dw_hdmi.c
>>>>>>> That driver checks for DRM_BRIDGE_ATTACH_NO_CONNECTOR being
>>>>>>> NOT present,
>>>>>>> since it wants to register its own connector through
>>>>>>> dw_hdmi_connector_create().
>>>>>>> It does it for a reason: the dw-hdmi is a multi-function
>>>>>>> driver which does
>>>>>>> HDMI and DDC/EDID stuff in a single driver (because I/O
>>>>>>> registers and power
>>>>>>> management seem to be shared).
>>>>>>
>>>>>> The IT66121 driver does all of that too, and does not need
>>>>>> DRM_BRIDGE_ATTACH_NO_CONNECTOR. The drm_bridge_funcs struct has
>>>>>> callbacks to handle cable detection and DDC stuff.
>>>>>>
>>>>>>> Since I do not see who could split this into a separate bridge
>>>>>>> and a connector driver
>>>>>>> and test it on multiple SoC platforms (there are at least 3 or
>>>>>>> 4), I think modifying
>>>>>>> the fundamentals of the dw-hdmi architecture just to get CI20
>>>>>>> HDMI working is not
>>>>>>> our turf.
>>>>>>
>>>>>> You could have a field in the dw-hdmi pdata structure, that
>>>>>> would
>>>>>> instruct the driver whether or not it should use the new API.
>>>>>> Ugly,
>>>>>> I know, and would probably duplicate a lot of code, but that
>>>>>> would
>>>>>> allow other drivers to be updated at a later date.
>>>>>
>>>>> Yes, would be very ugly.
>>>>>
>>>>> But generally who has the knowledge (and time) to do this work?
>>>>> And has a working platform to test (jz4780 isn't a good
>>>>> development environment)?
>>>>>
>>>>> The driver seems to have a turbulent history starting 2013 in
>>>>> staging/imx and
>>>>> apparently it was generalized since then... Is Laurent currently
>>>>> dw-hdmi maintainer?
>>>>
>>>> "Maintainer" would be an overstatement. I've worked on that
>>>> driver in
>>>> the past, and I still use it, but don't have time to really
>>>> maintain it.
>>>> I've also been told that Synopsys required all patches for that
>>>> driver
>>>> developed using documentation under NDA to be submitted
>>>> internally to
>>>> them first before being published, so I decided to stop
>>>> contributing
>>>> instead of agreeing with this insane process. There's public
>>>> documentation about the IP in some NXP reference manuals though,
>>>> so it
>>>> should be possible to still move forward without abiding by this
>>>> rule.
>>>>
>>>>>>> Therefore the code here should be able to detect if
>>>>>>> drm_bridge_attach() already
>>>>>>> creates and attaches a connector and then skip the code below.
>>>>>>
>>>>>> Not that easy, unfortunately. On one side we have dw-hdmi which
>>>>>> checks that DRM_BRIDGE_ATTACH_NO_CONNECTOR is not set, and on
>>>>>> the
>>>>>> other side we have other drivers like the IT66121 which will
>>>>>> fail if
>>>>>> this flag is not set.
>>>>>
>>>>> Ok, I see. You have to handle contradicting cases here.
>>>>>
>>>>> Would it be possible to run it with
>>>>> DRM_BRIDGE_ATTACH_NO_CONNECTOR first
>>>>> and retry if it fails without?
>>>>>
>>>>> But IMHO the return value (in error case) is not well defined.
>>>>> So there
>>>>> must be a test if a connector has been created (I do not know
>>>>> how this
>>>>> would work).
>>>>>
>>>>> Another suggestion: can you check if there is a downstream
>>>>> connector defined in
>>>>> device tree (dw-hdmi does not need such a definition)?
>>>>> If not we call it with 0 and if there is one we call it with
>>>>> DRM_BRIDGE_ATTACH_NO_CONNECTOR and create one?
>>>>
>>>> I haven't followed the ful conversation, what the reason why
>>>> DRM_BRIDGE_ATTACH_NO_CONNECTOR can't always be use here ?
>>>
>>> The synopsys driver creates its own connector through
>>> dw_hdmi_connector_create()
>>> because the IP handles DDC/EDID directly.
>>
>> That doesn't require creating a connector though. The driver
>> implements
>> drm_bridge_funcs.get_edid(), which is used to get the EDID without
>> the
>> need to create a connector in the dw-hdmi driver.
>
> Ah, ok.
>
> But then we still have issues.
>
> Firstly I would assume that get_edid only works properly if it is
> initialized
> through dw_hdmi_connector_create().
>
> Next, in the current code, passing DRM_BRIDGE_ATTACH_NO_CONNECTOR to
> dw_hdmi_bridge_attach() indeed does not call
> dw_hdmi_connector_create()
> but returns 0.
>
> This patch 6/6 makes drm/ingenic unconditionally require a connector
> to be attached which is defined somewhere else (device tree e.g.
> "connector-hdmi")
> unrelated to dw-hdmi. Current upstream code for drm/ingenic does not
> init/attach
> such a connector on its own so it did work before.
>
> I.e. I think we can't just use parts of dw-hdmi.

The fact that Laurent is using dw-hdmi with
DRM_BRIDGE_ATTACH_NO_CONNECTOR on Renesas makes me think that it's
possible here as well. There's no reason why it shouldn't work with
ingenic-drm.

The ingenic-drm driver does not need to create any connector. The
"connector-hdmi" is connected to dw-hdmi as the "next bridge" in the
list.

> If drm_bridge_attach() would return some errno if
> DRM_BRIDGE_ATTACH_NO_CONNECTOR
> is set, initialization in ingenic_drm_bind() would fail likewise with
> "Unable to attach bridge".
>
> So in any case dw-hdmi is broken by this drm/ingenic patch unless
> someone
> reworks it to make it compatible.

Where would the errno be returned? Why would drm_bridge_attach() return
an error code?

> Another issue is that dw_hdmi_connector_create() does not only do
> dcd/edid
> but appears to detects hot plug and does some special initialization.
> So we probably loose hotplug detect if we just use
> drm_bridge_funcs.get_edid().

There's drm_bridge_funcs.detect().

Cheers,
-Paul

> I come to the conclusion that not creating a specific connector in
> dw-hdmi
> and relying on a generic connector does not seem to be an option with
> current
> code proposals.
>
> In such a situation the question is what the least invasive surgery
> is to
> avoid complications and lenghty regression tests on unknown platforms.
> IMHO it is leaving (mature) dw-hdmi untouched and make attachment of
> a connector
> in ingenic_drm_bind() depend on some condition.
>
> BR and thanks,
> Nikolaus
>
>


\
 
 \ /
  Last update: 2021-09-23 15:31    [W:0.883 / U:0.428 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site