From: "james qian wang (Arm Technology China)" <james.qian.wang@arm.com>
To: Brian Starkey <Brian.Starkey@arm.com>
Cc: Mihail Atanassov <Mihail.Atanassov@arm.com>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
David Airlie <airlied@linux.ie>,
Liviu Dudau <Liviu.Dudau@arm.com>,
Russell King <linux@armlinux.org.uk>,
Maxime Ripard <mripard@kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
nd <nd@arm.com>, Sean Paul <sean@poorly.run>
Subject: Re: [RFC,3/3] drm/komeda: Allow non-component drm_bridge only endpoints
Date: Thu, 17 Oct 2019 03:07:59 +0000 [thread overview]
Message-ID: <20191017030752.GA3109@jamwan02-TSP300> (raw)
In-Reply-To: <20191016162206.u2yo37rtqwou4oep@DESKTOP-E1NTVVP.localdomain>
On Wed, Oct 16, 2019 at 04:22:07PM +0000, Brian Starkey wrote:
> Hi,
>
> On Wed, Oct 16, 2019 at 03:51:39PM +0000, Mihail Atanassov wrote:
> > Hi James,
> >
> > On Wednesday, 9 October 2019 06:54:15 BST james qian wang (Arm Technology China) wrote:
> > > On Fri, Oct 04, 2019 at 02:34:42PM +0000, Mihail Atanassov wrote:
> > > > To support transmitters other than the tda998x, we need to allow
> > > > non-component framework bridges to be attached to a dummy drm_encoder in
> > > > our driver.
> > > >
> > > > For the existing supported encoder (tda998x), keep the behaviour as-is,
> > > > since there's no way to unbind if a drm_bridge module goes away under
> > > > our feet.
> > > >
> > > > Signed-off-by: Mihail Atanassov <mihail.atanassov@arm.com>
> > > > ---
> > > > .../gpu/drm/arm/display/komeda/komeda_dev.h | 5 +
> > > > .../gpu/drm/arm/display/komeda/komeda_drv.c | 58 ++++++--
> > > > .../gpu/drm/arm/display/komeda/komeda_kms.c | 133 +++++++++++++++++-
> > > > .../gpu/drm/arm/display/komeda/komeda_kms.h | 5 +
> > > > 4 files changed, 187 insertions(+), 14 deletions(-)
> > > >
> > > > [snip]
> > > >
> > > > +static void komeda_encoder_destroy(struct drm_encoder *encoder)
> > > > +{
> > > > + drm_encoder_cleanup(encoder);
> > > > +}
> > > > +
> > > > +static const struct drm_encoder_funcs komeda_dummy_enc_funcs = {
> > > > + .destroy = komeda_encoder_destroy,
> > > > +};
> > > > +
> > > > +bool komeda_remote_device_is_component(struct device_node *local,
> > > > + u32 port, u32 endpoint)
> > > > +{
> > > > + struct device_node *remote;
> > > > + char const * const component_devices[] = {
> > > > + "nxp,tda998x",
> > >
> > > I really don't think put this dummy_encoder into komeda is a good
> > > idea.
> > >
> > > And I suggest to seperate this dummy_encoder to a individual module
> > > which will build the drm_ridge to a standard drm encoder and component
> > > based module, which will be enable by DT, totally transparent for komeda.
> > >
> > > BTW:
> > > I really don't like such logic: distingush the SYSTEM configuration
> > > by check the connected device name, it's hard to maintain and code
> > > sharing, and that's why NOW we have the device-tree.
>
> It's not ideal to have such special cases, for sure. However, I don't
> see this approach causing us any issues. tda998x really is "special",
> and as far as I can see the code here scales to other devices pretty
> easily.
>
> >
> > +Cc Brian
> >
> > I didn't think DT is the right place for pseudo-devices.
>
> I agree. DT should represent the HW, not the structure of the
> linux kernel subsystem.
>
> > The tda998x
> > looks to be in a small group of drivers that contain encoder +
> > bridge + connector; my impression of the current state of affairs is
> > that the drm_encoder tends to live where the CRTC provider is rather
> > than representing a HW entity (hence why drm_bridge based drivers
> > exist in drivers/gpu/drm/bridge). See the overview DOC comment in
> > drm_encoder.c ("drivers are free to use [drm_encoder] however they
> > wish"). I may be completely wrong, so would appreciate some
> > context and comment from others on the Cc list.
> >
> > In any case, converting a do-nothing dummy encoder into its own
> > component-module will add a lot more bloat compared to the current
> > ~10 SLoC implementation of the drm_encoder. probe/remove/bind/unbind,
> > a few extra structs here and there, yet another object file, DT
> > bindings, docs for the same, and maintaining all of that? It's a hard
> > sell for me. I'd prefer if we went ahead with the code as-is and fix it
> > up later if it really proves unwieldy and too hard to maintain. Could
> > this patch be improved? Sure! Can we improve it in follow-up work
> > though, as I think this is valuable enough on its own without any major
> > drawbacks?
> >
>
> Even if we implemented a separate component encoder, as far as I can
> tell there's no way to use it without either:
>
> a) sticking it in DT
> b) invoking it from komeda based on a "of_device_is_compatible" list
>
> IMO a) isn't acceptable, and b) doesn't have any advantages over this
> approach.
>
> > As per my cover letter, in an ideal world we'd have the encoder locally
> > and do drm_bridge_attach() even for tda998x, but the lifetime issues
> > around bridges inside modules mean that doing that now is a bit of a
> > step back for this specific case.
> >
>
> Yeah, my feeling is that being able to keep tda998x as a component
> (for the superior bind/unbind behaviour) is worth the slight ugliness,
> at least until bridges get the same functionality.
>
> If James is strongly against merging this, maybe we just swap
> wholesale to bridge? But for me, the pragmatic approach would be this
> stop-gap.
>
This is a good idea, and I vote +ULONG_MAX :)
and I also checked tda998x driver, it supports bridge. so swap the
wholesale to brige is perfect. :)
Thanks
James.
> Cheers,
> -Brian
>
> > >
> > > Thanks
> > > James
> > >
> > > > [snip]
> > >
> >
> > --
> > Mihail
> >
> >
> >
next prev parent reply other threads:[~2019-10-17 3:08 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-04 14:34 [PATCH 0/3] drm/komeda: Support for drm_bridge endpoints Mihail Atanassov
2019-10-04 14:34 ` [PATCH 1/3] drm/komeda: Consolidate struct komeda_drv allocations Mihail Atanassov
2019-10-04 14:34 ` [PATCH 2/3] drm/komeda: Memory manage struct komeda_drv in probe/remove Mihail Atanassov
2019-10-04 14:34 ` [RFC PATCH 3/3] drm/komeda: Allow non-component drm_bridge only endpoints Mihail Atanassov
2019-10-09 5:54 ` [RFC,3/3] " james qian wang (Arm Technology China)
2019-10-16 15:51 ` Mihail Atanassov
2019-10-16 16:22 ` Brian Starkey
2019-10-17 3:07 ` james qian wang (Arm Technology China) [this message]
2019-10-17 8:20 ` Brian Starkey
2019-10-17 10:21 ` james qian wang (Arm Technology China)
2019-10-17 10:48 ` Brian Starkey
2019-10-17 11:41 ` Russell King - ARM Linux admin
2019-10-18 6:57 ` james qian wang (Arm Technology China)
2019-10-18 9:12 ` Brian Starkey
2019-10-22 8:42 ` Daniel Vetter
2019-10-22 8:48 ` Russell King - ARM Linux admin
2019-10-22 8:50 ` Daniel Vetter
2019-10-22 14:42 ` Russell King - ARM Linux admin
2019-10-22 14:53 ` Russell King - ARM Linux admin
2019-10-24 8:03 ` Mihail Atanassov
2019-10-24 5:21 ` james qian wang (Arm Technology China)
2019-10-18 6:38 ` james qian wang (Arm Technology China)
2019-10-18 11:01 ` Mihail Atanassov
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