linux-kernel - Re: [PATCH v1 05/35] drm/connector: Add TV standard property

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Date:   Thu, 18 Aug 2022 01:23:12 +0200
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Jernej Skrabec <jernej.skrabec@...il.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Jerome Brunet <jbrunet@...libre.com>,
        Samuel Holland <samuel@...lland.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Daniel Vetter <daniel@...ll.ch>, Emma Anholt <emma@...olt.net>,
        David Airlie <airlied@...ux.ie>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Kevin Hilman <khilman@...libre.com>,
        Neil Armstrong <narmstrong@...libre.com>,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Phil Elwell <phil@...pberrypi.com>,
        Mateusz Kwiatkowski <kfyatek+publicgit@...il.com>,
        linux-arm-kernel@...ts.infradead.org,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        linux-amlogic@...ts.infradead.org, dri-devel@...ts.freedesktop.org,
        Dom Cobley <dom@...pberrypi.com>,
        Noralf Trønnes <noralf@...nnes.org>
Subject: Re: [PATCH v1 05/35] drm/connector: Add TV standard property



Den 17.08.2022 15.11, skrev Noralf Trønnes:
> 
> 
> Den 17.08.2022 13.46, skrev Maxime Ripard:
>> On Tue, Aug 16, 2022 at 09:35:24PM +0200, Noralf Trønnes wrote:
>>> Den 16.08.2022 11.49, skrev Maxime Ripard:
>>>> On Tue, Aug 16, 2022 at 11:42:20AM +0200, Noralf Trønnes wrote:
>>>>> Den 16.08.2022 10.26, skrev Maxime Ripard:
>>>>>> Hi,
>>>>>>
>>>>>> On Mon, Aug 08, 2022 at 02:44:56PM +0200, Noralf Trønnes wrote:
>>>>>>> Den 29.07.2022 18.34, skrev Maxime Ripard:
>>>>>>>> The TV mode property has been around for a while now to select and get the
>>>>>>>> current TV mode output on an analog TV connector.
>>>>>>>>
>>>>>>>> Despite that property name being generic, its content isn't and has been
>>>>>>>> driver-specific which makes it hard to build any generic behaviour on top
>>>>>>>> of it, both in kernel and user-space.
>>>>>>>>
>>>>>>>> Let's create a new bitmask tv norm property, that can contain any of the
>>>>>>>> analog TV standards currently supported by kernel drivers. Each driver can
>>>>>>>> then pass in a bitmask of the modes it supports.
>>>>>>>>
>>>>>>>> We'll then be able to phase out the older tv mode property.
>>>>>>>>
>>>>>>>> Signed-off-by: Maxime Ripard <maxime@...no.tech>
>>>>>>>>

>>> How do you test the property? I've used modetest but I can only change
>>> to a tv.mode that matches the current display mode. I can't switch from
>>> ntsc to pal for instance.
>>
>> Yep, if you want to change from PAL to NTSC, it will require a new mode.
>>
> 
> So userspace has to check tv.mode first and then create a display mode
> the driver will accept if switching to a different display mode is
> necessary? In other words, userspace can't discover from the kernel
> which display modes a certain tv.mode/norm provides before it is
> selected? If so, maybe libdrm should have some function(s) to deal with
> switching between modes that require a different display mode since
> knowledge about which display modes a tv.mode supports is needed before
> hand.
> 

I haven't used vc4 on Pi4 in mainline before and have finally gotten it
to work.

I see that the connector reports 2 modes that together fit all tv.norms
so userspace doesn't have to contruct a display mode, but it does need
to know which display mode belongs to a certain tv.norm.

When I try to use modetest I'm unable to set a mode:

pi@...t:~ $ modetest -M vc4 -s 45:720x480i
setting mode 720x480i-29.97Hz on connectors 45, crtc 68
failed to set mode: Function not implemented

The errno is misleading, modetest does a drmModeDirtyFB before checking
the error returned by drmModeSetCrtc.

Setting the property succeeds, but the modeset still fails:

pi@...t:~ $ modetest -M vc4 -s 45:720x480i -w 45:"tv norm":2
setting mode 720x480i-29.97Hz on connectors 45, crtc 68
failed to set mode: Function not implemented

pi@...t:~ $ modetest -M vc4 -c
        37 tv norm:
                flags: bitmask
                values: NTSC-443=0x1 NTSC-J=0x2 NTSC-M=0x4 PAL-B=0x10
PAL-M=0x200 PAL-N=0x400 SECAM-B=0x2000
                value: 2

Here's the log, can you see if there's anything obvious in there:
https://gist.github.com/notro/a079498bf6b64327105752b2bafa8858

Noralf.