Message-ID: <CAA8EJpo1KhzTpaSqjbOuQvNKw4WGaqrtNBtNfdNLn28eZVgwhw@mail.gmail.com>
Date:   Thu, 16 Nov 2023 17:23:09 +0200
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Sui Jingfeng <sui.jingfeng@...ux.dev>
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

On Thu, 16 Nov 2023 at 14:08, Sui Jingfeng <sui.jingfeng@...ux.dev> wrote:
>
>
> On 2023/11/16 19:53, Sui Jingfeng wrote:
> > Hi,
> >
> >
> > On 2023/11/16 19:29, Dmitry Baryshkov wrote:
> >> On Thu, 16 Nov 2023 at 13:18, Sui Jingfeng <sui.jingfeng@...ux.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.

Because the monitor is not a part of the display pipeline.

> >
> >
> >>> 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.
> >
>
> 'identify' -> 'identity'
>
>
> >
> >> 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!

>From my point of view: no.

-- 
With best wishes
Dmitry

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