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Date:   Thu, 16 Nov 2023 19:53:12 +0800
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Subject: Re: [PATCH 8/8] drm/bridge: it66121: Allow link this driver as a lib
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To:     Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Cc:     Phong LE <ple@baylibre.com>,
        Neil Armstrong <neil.armstrong@linaro.org>,
        Maxime Ripard <mripard@kernel.org>,
        Sui Jingfeng <suijingfeng@loongson.cn>,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org,
        Laurent Pinchart <Laurent.pinchart@ideasonboard.com>,
        Thomas Zimmermann <tzimmermann@suse.de>
References: <20231114150130.497915-1-sui.jingfeng@linux.dev>
 <20231114150130.497915-9-sui.jingfeng@linux.dev>
 <CAA8EJprQq3aDhzE+yKGZ2-nsuHWcptzMvApsyOi9D63PgeiZ3w@mail.gmail.com>
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 <CAA8EJppY2+ymX0kLY+cuR=SV1Po2J24r=NQecmb3ZhSE9NHG7Q@mail.gmail.com>
From:   Sui Jingfeng <sui.jingfeng@linux.dev>
In-Reply-To: <CAA8EJppY2+ymX0kLY+cuR=SV1Po2J24r=NQecmb3ZhSE9NHG7Q@mail.gmail.com>
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Hi,


On 2023/11/16 19:29, Dmitry Baryshkov wrote:
> On Thu, 16 Nov 2023 at 13:18, Sui Jingfeng <sui.jingfeng@linux.dev> wrote:
>> Hi,
>>
>>
>> On 2023/11/15 00:30, Dmitry Baryshkov wrote:
>>>> +
>>>> +               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"
>>>>    };
>>>>
>>>> -static int it66121_probe(struct i2c_client *client)
>>>> +int it66121_create_bridge(struct i2c_client *client, bool of_support,
>>>> +                         bool hpd_support, bool audio_support,
>>>> +                         struct drm_bridge **bridge)
>>>>    {
>>>> +       struct device *dev = &client->dev;
>>>>           int ret;
>>>>           struct it66121_ctx *ctx;
>>>> -       struct device *dev = &client->dev;
>>>> -
>>>> -       if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C)) {
>>>> -               dev_err(dev, "I2C check functionality failed.\n");
>>>> -               return -ENXIO;
>>>> -       }
>>>>
>>>>           ctx = devm_kzalloc(dev, sizeof(*ctx), GFP_KERNEL);
>>>>           if (!ctx)
>>>> @@ -1649,24 +1665,19 @@ static int it66121_probe(struct i2c_client *client)
>>>>
>>>>           ctx->dev = dev;
>>>>           ctx->client = client;
>>>> -       ctx->info = i2c_get_match_data(client);
>>>> -
>>>> -       ret = it66121_of_read_bus_width(dev, &ctx->bus_width);
>>>> -       if (ret)
>>>> -               return ret;
>>>> -
>>>> -       ret = it66121_of_get_next_bridge(dev, &ctx->next_bridge);
>>>> -       if (ret)
>>>> -               return ret;
>>>> -
>>>> -       i2c_set_clientdata(client, ctx);
>>>>           mutex_init(&ctx->lock);
>>>>
>>>> -       ret = devm_regulator_bulk_get_enable(dev, ARRAY_SIZE(it66121_supplies),
>>>> -                                            it66121_supplies);
>>>> -       if (ret) {
>>>> -               dev_err(dev, "Failed to enable power supplies\n");
>>>> -               return ret;
>>>> +       if (of_support) {
>>>> +               ret = it66121_of_read_bus_width(dev, &ctx->bus_width);
>>>> +               if (ret)
>>>> +                       return ret;
>>>> +
>>>> +               ret = it66121_of_get_next_bridge(dev, &ctx->next_bridge);
>>>> +               if (ret)
>>>> +                       return ret;
>>>> +       } else {
>>>> +               ctx->bus_width = 24;
>>>> +               ctx->next_bridge = NULL;
>>>>           }
>>> A better alternative would be to turn OF calls into fwnode calls and
>>> to populate the fwnode properties. See
>>> drivers/platform/x86/intel/chtwc_int33fe.c for example.
>>
>> Honestly, I don't want to leave any scratch(breadcrumbs).
>> I'm worries about that turn OF calls into fwnode calls will leave something unwanted.
>>
>> Because I am not sure if fwnode calls will make sense in the DT world, while my patch
>> *still* be useful in the DT world.
> fwnode calls work for both DT and non-DT cases. In the DT case they
> work with DT nodes and properties. In the non-DT case, they work with
> manually populated properties.
>
>> Because the newly introduced it66121_create_bridge()
>> function is a core. I think It's better leave this task to a more advance programmer.
>> if there have use case. It can be introduced at a latter time, probably parallel with
>> the DT.
>>
>> I think DT and/or ACPI is best for integrated devices, but it66121 display bridges is
>> a i2c slave device. Personally, I think slave device shouldn't be standalone. I'm more
>> prefer to turn this driver to support hot-plug, even remove the device on the run time
>> freely when detach and allow reattach. Like the I2C EEPROM device in the monitor (which
>> contains the EDID, with I2C slave address 0x50). The I2C EEPROM device *also* don't has
>> a corresponding struct device representation in linux kernel.
> It has. See i2c_client::dev.

No, what I mean is that there don't have a device driver for monitor(display) hardware entity.
And the drm_do_probe_ddc_edid() is the static linked driver, which is similar with the idea
this series want to express.


>> so I still think It is best to make this drivers functional as a static lib, but I want
>> to hear you to say more. Why it would be a *better* alternative to turn OF calls into
>> fwnode calls? what are the potential benefits?
> Because then you can populate device properties from your root device.
> Because it allows the platform to specify the bus width instead of
> hardcoding 24 bits (which might work in your case, but might not be
> applicable to another user next week).


No, this problem can be easily solved. Simply add another argument.

```

int it66121_create_bridge(struct i2c_client *client, bool of_support,
                           bool hpd_support, bool audio_support, u32 bus_width,
                           struct drm_bridge **bridge);
```


> Anyway, even without fwnode, I'd strongly suggest you to drop the
> it66121_create_bridge() as it is now and start by populating the i2c
> bus from your root device.

This will force all non-DT users to add the similar code patter at the display controller side,
which is another kind of duplication. The monitor is also as I2C slave device, can be abstract
as a identify drm bridges in theory, I guess.


> Then you will need some way (fwnode?) to
> discover the bridge chain. And at the last point you will get into the
> device data and/or properties business.
>
No, leave that chance to a more better programmer and forgive me please,
too difficult, I'm afraid of not able to solve. Thanks a lot for the trust!