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

Sui Jingfeng
2023-11-16T11:53:26Z

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!