linux-kernel - Re: [PATCH 8/8] drm/bridge: it66121: Allow link this driver as a lib

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Message-ID: <79301d04-c0cb-4740-8a6d-27a889b65daf@linux.dev>
Date:   Thu, 16 Nov 2023 17:14:34 +0800
From:   Sui Jingfeng <sui.jingfeng@...ux.dev>
To:     Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Cc:     Phong LE <ple@...libre.com>,
        Neil Armstrong <neil.armstrong@...aro.org>,
        Maxime Ripard <mripard@...nel.org>,
        Sui Jingfeng <suijingfeng@...ngson.cn>,
        linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
        Thomas Zimmermann <tzimmermann@...e.de>
Subject: Re: [PATCH 8/8] drm/bridge: it66121: Allow link this driver as a lib

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@...ux.dev> wrote:
>> From: Sui Jingfeng <suijingfeng@...ngson.cn>
>>
>> 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@...ngson.cn>
>> ---
>>   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.

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.


>> +
>> +               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"
>>   };
>