Date:   Tue, 2 Jul 2019 12:12:26 +0200 (CEST)
From:   Nikolaus Voss <nv@...n.de>
To:     "Andrew F. Davis" <afd@...com>
cc:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        Andreas Dannenberg <dannenberg@...com>,
        Kate Stewart <kstewart@...uxfoundation.org>,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 1/2] ASoC: tas5720.c: cleanup variant management

On Mon, 1 Jul 2019, Andrew F. Davis wrote:
> On 7/1/19 11:35 AM, Nikolaus Voss wrote:
>> On Mon, 1 Jul 2019, Andrew F. Davis wrote:
>>> On 7/1/19 9:42 AM, Nikolaus Voss wrote:
>>>> Replace enum tas572x_type with struct tas5720_variant which aggregates
>>>> variant specific stuff and can be directly referenced from an id table.
>>>>
>>>> Signed-off-by: Nikolaus Voss <nikolaus.voss@...wensteinmedical.de>
>>>> ---
>>>>  sound/soc/codecs/tas5720.c | 98 +++++++++++++-------------------------
>>>>  1 file changed, 33 insertions(+), 65 deletions(-)
>>>>
>>>> diff --git a/sound/soc/codecs/tas5720.c b/sound/soc/codecs/tas5720.c
>>>> index 37fab8f22800..b2e897f094b4 100644
>>>> --- a/sound/soc/codecs/tas5720.c
>>>> +++ b/sound/soc/codecs/tas5720.c
>>>> @@ -28,9 +28,10 @@
>>>>  /* Define how often to check (and clear) the fault status register
>>>> (in ms) */
>>>>  #define TAS5720_FAULT_CHECK_INTERVAL        200
>>>>
>>>> -enum tas572x_type {
>>>> -    TAS5720,
>>>> -    TAS5722,
>>>> +struct tas5720_variant {
>>>> +    const int device_id;
>>>> +    const struct regmap_config *reg_config;
>>>> +    const struct snd_soc_component_driver *comp_drv;
>>>>  };
>>>>
>>>>  static const char * const tas5720_supply_names[] = {
>>>> @@ -44,7 +45,7 @@ struct tas5720_data {
>>>>      struct snd_soc_component *component;
>>>>      struct regmap *regmap;
>>>>      struct i2c_client *tas5720_client;
>>>> -    enum tas572x_type devtype;
>>>> +    const struct tas5720_variant *variant;
>>>
>>> Why add a new struct? Actually I don't see the need for this patch at
>>> all, the commit message only explains the 'what' not the 'why'. We can
>>> and do already build this info from the tas572x_type.
>>
>> As the commit message says, the purpose is to aggregate the variant
>> specifics and make it accessible via one pointer. This is a standard
>> approach for of/acpi_device_id tables and thus makes the code simpler
>> and improves readability. This is a maintenance patch to prepare using
>> the device match API in a proper way.
>>
>
>
> "make it accessible via one pointer" is again a "what", the "why" is:
>
> "This is a standard approach"
> "makes the code simpler and improves readability"
>
> Those are valid reasons and should be what you put in the commit message.

ok

>
>
>>>
>>> Also below are several functional changes, the cover letter says this is
>>> not a functional change, yet the driver behaves differently now.
>>
>> Can you be a little bit more specific? The code should behave exactly as
>> before.
>>
>
>
> Sure, for instance the line "unexpected private driver data" is removed,
> this can now never happen, that is a functional change. The phrase "no
> functional change", should be reserved for only changes to spelling,
> formatting, code organizing, etc..

"unexpected private driver data" was unreachable code before, but you're 
right, debug output has changed a little, but the functional part is 
exactly the same.

>
>
>> Niko
>>
>>>
>>> Andrew
>>>
>>>>      struct regulator_bulk_data supplies[TAS5720_NUM_SUPPLIES];
>>>>      struct delayed_work fault_check_work;
>>>>      unsigned int last_fault;
>>>> @@ -179,17 +180,13 @@ static int tas5720_set_dai_tdm_slot(struct
>>>> snd_soc_dai *dai,
>>>>          goto error_snd_soc_component_update_bits;
>>>>
>>>>      /* Configure TDM slot width. This is only applicable to TAS5722. */
>>>> -    switch (tas5720->devtype) {
>>>> -    case TAS5722:
>>>> +    if (tas5720->variant->device_id == TAS5722_DEVICE_ID) {
>
>
> I also don't like this, TAS5722_DEVICE_ID is the expected contents of a
> register, you are using it like the enum tas572x_type that you removed.
> I'd leave that enum, the device ID register itself is not guaranteed to
> be correct or unique, which is why we warn about mismatches below but
> then continue to use the user provided device type anyway.

Strange, with me it's the other way round, I don't like the enum. The 
mismatch behavior hasn't changed a bit, the same warning is printed. 
If the device ID is no longer unique in the future (apparently it is 
for now) the driver should explicitly handle this instead of printing a 
warning, because warnings should be reserved for an indication of any 
kind of misconfiguration and not of expected behavior.

That said the variant struct can of course replace the enum in every 
aspect, even for what you describe above. The enum was an ordinal 
representation of the user-selected i2c_device_id, the variant struct* is
a pointer representation of the user-selected i2c/of/acpi_device_id. The 
only difference is that it directly points to the variant specific parts 
of the driver instead of resolving those via multiple switch/case 
statements.

Niko

>
> Andrew
>
>
>>>>          ret = snd_soc_component_update_bits(component,
>>>> TAS5722_DIGITAL_CTRL2_REG,
>>>>                              TAS5722_TDM_SLOT_16B,
>>>>                              slot_width == 16 ?
>>>>                              TAS5722_TDM_SLOT_16B : 0);
>>>>          if (ret < 0)
>>>>              goto error_snd_soc_component_update_bits;
>>>> -        break;
>>>> -    default:
>>>> -        break;
>>>>      }
>>>>
>>>>      return 0;
>>>> @@ -277,7 +274,7 @@ static void tas5720_fault_check_work(struct
>>>> work_struct *work)
>>>>  static int tas5720_codec_probe(struct snd_soc_component *component)
>>>>  {
>>>>      struct tas5720_data *tas5720 =
>>>> snd_soc_component_get_drvdata(component);
>>>> -    unsigned int device_id, expected_device_id;
>>>> +    unsigned int device_id;
>>>>      int ret;
>>>>
>>>>      tas5720->component = component;
>>>> @@ -301,21 +298,9 @@ static int tas5720_codec_probe(struct
>>>> snd_soc_component *component)
>>>>          goto probe_fail;
>>>>      }
>>>>
>>>> -    switch (tas5720->devtype) {
>>>> -    case TAS5720:
>>>> -        expected_device_id = TAS5720_DEVICE_ID;
>>>> -        break;
>>>> -    case TAS5722:
>>>> -        expected_device_id = TAS5722_DEVICE_ID;
>>>> -        break;
>>>> -    default:
>>>> -        dev_err(component->dev, "unexpected private driver data\n");
>>>> -        return -EINVAL;
>>>> -    }
>>>> -
>>>> -    if (device_id != expected_device_id)
>>>> +    if (device_id != tas5720->variant->device_id)
>>>>          dev_warn(component->dev, "wrong device ID. expected: %u
>>>> read: %u\n",
>>>> -             expected_device_id, device_id);
>>>> +             tas5720->variant->device_id, device_id);
>>>>
>>>>      /* Set device to mute */
>>>>      ret = snd_soc_component_update_bits(component,
>>>> TAS5720_DIGITAL_CTRL2_REG,
>>>> @@ -637,7 +622,6 @@ static int tas5720_probe(struct i2c_client *client,
>>>>  {
>>>>      struct device *dev = &client->dev;
>>>>      struct tas5720_data *data;
>>>> -    const struct regmap_config *regmap_config;
>>>>      int ret;
>>>>      int i;
>>>>
>>>> @@ -646,20 +630,10 @@ static int tas5720_probe(struct i2c_client
>>>> *client,
>>>>          return -ENOMEM;
>>>>
>>>>      data->tas5720_client = client;
>>>> -    data->devtype = id->driver_data;
>>>>
>>>> -    switch (id->driver_data) {
>>>> -    case TAS5720:
>>>> -        regmap_config = &tas5720_regmap_config;
>>>> -        break;
>>>> -    case TAS5722:
>>>> -        regmap_config = &tas5722_regmap_config;
>>>> -        break;
>>>> -    default:
>>>> -        dev_err(dev, "unexpected private driver data\n");
>>>> -        return -EINVAL;
>>>> -    }
>>>> -    data->regmap = devm_regmap_init_i2c(client, regmap_config);
>>>> +    data->variant = (const struct tas5720_variant *)id->driver_data;
>>>> +
>>>> +    data->regmap = devm_regmap_init_i2c(client,
>>>> data->variant->reg_config);
>>>>      if (IS_ERR(data->regmap)) {
>>>>          ret = PTR_ERR(data->regmap);
>>>>          dev_err(dev, "failed to allocate register map: %d\n", ret);
>>>> @@ -678,42 +652,36 @@ static int tas5720_probe(struct i2c_client
>>>> *client,
>>>>
>>>>      dev_set_drvdata(dev, data);
>>>>
>>>> -    switch (id->driver_data) {
>>>> -    case TAS5720:
>>>> -        ret = devm_snd_soc_register_component(&client->dev,
>>>> -                    &soc_component_dev_tas5720,
>>>> -                    tas5720_dai,
>>>> -                    ARRAY_SIZE(tas5720_dai));
>>>> -        break;
>>>> -    case TAS5722:
>>>> -        ret = devm_snd_soc_register_component(&client->dev,
>>>> -                    &soc_component_dev_tas5722,
>>>> -                    tas5720_dai,
>>>> -                    ARRAY_SIZE(tas5720_dai));
>>>> -        break;
>>>> -    default:
>>>> -        dev_err(dev, "unexpected private driver data\n");
>>>> -        return -EINVAL;
>>>> -    }
>>>> -    if (ret < 0) {
>>>> -        dev_err(dev, "failed to register component: %d\n", ret);
>>>> -        return ret;
>>>> -    }
>>>> -
>>>> -    return 0;
>>>> +    ret = devm_snd_soc_register_component(&client->dev,
>>>> +                          data->variant->comp_drv,
>>>> +                          tas5720_dai,
>>>> +                          ARRAY_SIZE(tas5720_dai));
>>>> +    return ret;
>>>>  }
>>>>
>>>> +static const struct tas5720_variant tas5720 = {
>>>> +    .device_id = TAS5720_DEVICE_ID,
>>>> +    .reg_config = &tas5720_regmap_config,
>>>> +    .comp_drv = &soc_component_dev_tas5720,
>>>> +};
>>>> +
>>>> +static const struct tas5720_variant tas5722 = {
>>>> +    .device_id = TAS5722_DEVICE_ID,
>>>> +    .reg_config = &tas5722_regmap_config,
>>>> +    .comp_drv = &soc_component_dev_tas5722,
>>>> +};
>>>> +
>>>>  static const struct i2c_device_id tas5720_id[] = {
>>>> -    { "tas5720", TAS5720 },
>>>> -    { "tas5722", TAS5722 },
>>>> +    { "tas5720", (kernel_ulong_t)&tas5720 },
>>>> +    { "tas5722", (kernel_ulong_t)&tas5722 },
>>>>      { }
>>>>  };
>>>>  MODULE_DEVICE_TABLE(i2c, tas5720_id);
>>>>
>>>>  #if IS_ENABLED(CONFIG_OF)
>>>>  static const struct of_device_id tas5720_of_match[] = {
>>>> -    { .compatible = "ti,tas5720", },
>>>> -    { .compatible = "ti,tas5722", },
>>>> +    { .compatible = "ti,tas5720", .data = &tas5720, },
>>>> +    { .compatible = "ti,tas5722", .data = &tas5722, },
>>>>      { },
>>>>  };
>>>>  MODULE_DEVICE_TABLE(of, tas5720_of_match);
>>>>
>>>
>

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