Re: [PATCH 8/8] drm/bridge: it66121: Allow link this driver as a lib
From: Neil Armstrong
Date: Thu Nov 23 2023 - 08:40:08 EST
On 23/11/2023 09:08, Dmitry Baryshkov wrote:
On Thu, 23 Nov 2023 at 07:05, Sui Jingfeng <sui.jingfeng@xxxxxxxxx> wrote:
Hi,
On 2023/11/16 19:19, Dmitry Baryshkov wrote:
On Thu, 16 Nov 2023 at 12:13, Sui Jingfeng <sui.jingfeng@xxxxxxxxx> wrote:
Hi,
On 2023/11/16 17:30, Dmitry Baryshkov wrote:
On Thu, 16 Nov 2023 at 11:14, Sui Jingfeng <sui.jingfeng@xxxxxxxxx> wrote:
Hi,
Thanks a lot for reviewing!
On 2023/11/15 00:30, Dmitry Baryshkov wrote:
On Tue, 14 Nov 2023 at 17:09, Sui Jingfeng <sui.jingfeng@xxxxxxxxx> wrote:
From: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
The it66121_create_bridge() and it66121_destroy_bridge() are added to
export the core functionalities. Create a connector manually by using
bridge connector helpers when link as a lib.
Signed-off-by: Sui Jingfeng <suijingfeng@xxxxxxxxxxx>
---
drivers/gpu/drm/bridge/ite-it66121.c | 134 +++++++++++++++++++--------
include/drm/bridge/ite-it66121.h | 17 ++++
2 files changed, 113 insertions(+), 38 deletions(-)
create mode 100644 include/drm/bridge/ite-it66121.h
diff --git a/drivers/gpu/drm/bridge/ite-it66121.c b/drivers/gpu/drm/bridge/ite-it66121.c
index 8971414a2a60..f5968b679c5d 100644
--- a/drivers/gpu/drm/bridge/ite-it66121.c
+++ b/drivers/gpu/drm/bridge/ite-it66121.c
@@ -22,6 +22,7 @@
#include <drm/drm_atomic_helper.h>
#include <drm/drm_bridge.h>
+#include <drm/drm_bridge_connector.h>
#include <drm/drm_edid.h>
#include <drm/drm_modes.h>
#include <drm/drm_print.h>
@@ -703,14 +704,32 @@ static int it66121_bridge_attach(struct drm_bridge *bridge,
enum drm_bridge_attach_flags flags)
{
struct it66121_ctx *ctx = bridge_to_it66121(bridge);
+ struct drm_bridge *next_bridge = ctx->next_bridge;
+ struct drm_encoder *encoder = bridge->encoder;
int ret;
- if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR))
- return -EINVAL;
+ if (next_bridge) {
+ if (!(flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)) {
+ WARN_ON(1);
Why? At least use WARN() instead
Originally I want to
+ flags |= DRM_BRIDGE_ATTACH_NO_CONNECTOR;
+ }
+ ret = drm_bridge_attach(encoder, next_bridge, bridge, flags);
+ if (ret)
+ return ret;
+ } else {
+ struct drm_connector *connector;
- ret = drm_bridge_attach(bridge->encoder, ctx->next_bridge, bridge, flags);
- if (ret)
- return ret;
+ if (flags & DRM_BRIDGE_ATTACH_NO_CONNECTOR)
+ WARN_ON(1);
No. It is perfectly fine to create attach a bridge with no next_bridge
and with the DRM_BRIDGE_ATTACH_NO_CONNECTOR flag.
The document say when DRM_BRIDGE_ATTACH_NO_CONNECTOR flag is set
the bridge shall not create a drm_connector. So I think if a display
bridge driver don't have a next bridge attached (Currently, this is
told by the DT), it says that this is a non-DT environment. On such
a case, this display bridge driver(it66121.ko) should behavior like
a *agent*. Because the upstream port of it66121 is the DVO port of
the display controller, the downstream port of it66121 is the HDMI
connector. it66121 is on the middle. So I think the it66121.ko should
handle all of troubles on behalf of the display controller drivers.
No. Don't make decisions for the other drivers. They might have different needs.
[...]
Therefore (when in non-DT use case), the display controller drivers
side should not set DRM_BRIDGE_ATTACH_NO_CONNECTOR flag anymore.
Which is to hint that the it66121 should totally in charge of those
tasks (either by using bridge connector helper or create a connector
manually). I don't understand on such a case, why bother display
controller drivers anymore.
This is the reason why we had introduced this flag. It allows the
driver to customise the connector. It even allows the driver to
implement a connector on its own, completely ignoring the
drm_bridge_connector.
I know what you said is right in the sense of the universe cases,
but I think the most frequent(majority) use case is that there is
only one display bridge on the middle. Therefore, I don't want to
movethe connector things into device driver if there is only one display
bridge(say it66121) in the middle. After all, there is no *direct
physical connection* from the perspective of the hardware. I means that
there is no hardware wires connectthe HDMI connector and the DVO port. So display controller drivers
should not interact with anything related with the connector on a
perfect abstract on the software side. Especially for such a simple use
case. It probably make senses to make a decision for themost frequently use case, please also note
that this patch didn't introduce any-restriction for the more advance
uses cases(multiple bridges in the middle).
So, for the sake of not having the connector in the display driver,
you want to add boilerplate code basically to each and every bridge
driver. In the end, they should all behave in the same way.
Moreover, there is no way this implementation can work without a
warning if there are two bridges in a chain and the it66121 is the
second (the last) one. The host can not specify the
DRM_BRIDGE_ATTACH_NO_CONNECTOR)
+ WARN_ON(1);
No. It is perfectly fine to create attach a bridge with no next_bridge
and with the DRM_BRIDGE_ATTACH_NO_CONNECTOR flag.
The document say when DRM_BRIDGE_ATTACH_NO_CONNECTOR flag is set
the bridge shall not create a drm_connector. So I think if a display
bridge driver don't have a next bridge attached (Currently, this is
told by the DT), it says that this is a non-DT environment. On such
a case, this display bridge driver(it66121.ko) should behavior like
a *agent*. Because the upstream port of it66121 is the DVO port of
the display controller, the downstream port of it66121 is the HDMI
connector. it66121 is on the middle. So I think the it66121.ko should
handle all of troubles on behalf of the display controller drivers.
No. Don't make decisions for the other drivers. They might have different needs.
[...]
Therefore (when in non-DT use case), the display controller drivers
side should not set DRM_BRIDGE_ATTACH_NO_CONNECTOR flag anymore.
Which is to hint that the it66121 should totally in charge of those
tasks (either by using bridge connector helper or create a connector
manually). I don't understand on such a case, why bother display
controller drivers anymore.
This is the reason why we had introduced this flag. It allows the
driver to customise the connector. It even allows the driver to
implement a connector on its own, completely ignoring the
drm_bridge_connector.
I know what you said is right in the sense of the universe cases,
but I think the most frequent(majority) use case is that there is
only one display bridge on the middle. Therefore, I don't want to
movethe connector things into device driver if there is only one display
bridge(say it66121) in the middle. After all, there is no *direct
physical connection* from the perspective of the hardware. I means that
there is no hardware wires connectthe HDMI connector and the DVO port. So display controller drivers
should not interact with anything related with the connector on a
perfect abstract on the software side. Especially for such a simple use
case. It probably make senses to make a decision for themost frequently use case, please also note
that this patch didn't introduce any-restriction for the more advance
uses cases(multiple bridges in the middle).
So, for the sake of not having the connector in the display driver,
you want to add boilerplate code basically to each and every bridge
driver. In the end, they should all behave in the same way.
No, I'm only intend to modify the one when there has a user emerged.
If we have the connector related code in the KMS display driver side,
then I think we don't honor the meaning of the word *bridge*. I was
told drm_bridge is a modern design, if we still need the DC side
worry about something do not have a physical connection, then it will
not be modern anymore, it is not a good bridge.
Next time the user emerges for another bridge. And then for another.
This way the very similar code is copy-pasted over all bridge drivers.
So instead it was decided to keep it in the display driver code.
Moreover, there is no way this implementation can work without a
warning if there are two bridges in a chain and the it66121 is the
second (the last) one.
Yes and no!
If one of them are transparent, then thisimplementation still can works. It is just that this will not be a good
abstract anymore.I do have seen such design on some notebook hardware. But from my programming experiences,
using two bridges are typically a bad practice in engineering. As it tend
to increase the PCB board area and increase entire cost. As you need buy
one more TX encoder chip. Please also consider that the embedded world focus
on low cost and low power consume.
A typical pipeline for an embedded device can perfectly look like:
- DSI host (drm_encoder)
- DSI-HDMI or DSI-eDP bridge (drm_bridge)
- hdmi-connector or panel-bridge (drm_bridge)
- drm_bridge_connector.
Two drm_bridge instances.
Nowadays, we are moving the encoder code into bridge so we can have way
more than 2 bridges, and connector code has been moved to a bridge.
On Amlogic SoCs, the HDMI chain has at least 3 bridges, it can have up to 4
on DSI usecase if you plug a DSI to eDP bridge.
On iMX8 platform, they have multiple internal SoC bridges even before the HDMI or DSI bridge.
The model works very well across extremely heterogeneous embedded platforms.
I think, multiple display bridges case should be avoided for middle/low end
application. Or allow us to handle the two and/or more bridges cases in the
future. When there has at least one user emerged, we will introduce new
approach to handle then.
Do you find any product level boards that using two external display bridge and
one of them is it66121? If we can not even find a user, we are not even have a
board to test if current design (state of art) works. Does it suffer from module
loading order problems? what if their i2c slave address is same? Does such a use
case will past the S3/S4 test? All of those concerns are imposed to every display
bridges programmer from the very beginning.
Please add a hdmi-connector device to your testing model. You don't
have to use it, but it is a fully legit use case. And suddenly you
have to drm_bridge instances in your chain.
I'm agree with the idea that drm bridges drivers involved toward to a direction
that support more complex design, but I think we should also leave a way for the
most frequent use case. Make it straight-forward as a canonical design.
Not having anything connector-related in the drm_bridge driver is a
canonical design.
The host can not specify the
DRM_BRIDGE_ATTACH_NO_CONNECTOR flag, it will cause a warning here. And
it can not omit the flag (as otherwise the first bridge will create a
connector, without consulting the second bridge).
The semantics of DRM_BRIDGE_ATTACH_NO_CONNECTOR flagare implement-defined,
No, they are not. Semantics are pretty simple: do not create the
drm_connector instance. Pass the flag to the next bridge in the chain.
for our case, I could just ignore it if their
don't have a signal(DT or ACPI) tell me that there are multiple bridges
in the chain. This depend on community's attitude.
Ignoring a flag is a bad idea.
For it66121 with a canonical design, the host should not need to specify this flag.
Because at the time of when the device driver(it66121.ko) get loaded, the it66121
driver could parse the DT by itself, and detect if there has a next bridge, is it a
connector or is it yet another display bridges. The DT speak everything about the
topology. The flag is there just for the KMS display controller driver to explicit
control, use it and make it more useful is the right way, is it?
No. We have been there (before the DRM_BRIDGE_ATTACH_NO_CONNECTOR was
introduced), we have gone away from it.
+
+ connector = drm_bridge_connector_init(bridge->dev, encoder);
+ if (IS_ERR(connector))
+ return PTR_ERR(connector);
+
+ drm_connector_attach_encoder(connector, encoder);
This goes into your device driver.
+
+ ctx->connector = connector;
+ }
if (ctx->info->id == ID_IT66121) {
ret = regmap_write_bits(ctx->regmap, IT66121_CLK_BANK_REG,
@@ -1632,16 +1651,13 @@ static const char * const it66121_supplies[] = {
"vcn33", "vcn18", "vrf12"
};