[PATCH v3 1/2] drm/bridge: add Silicon Image SiI9234 driver

[Marek Szyprowski]

Hi Krzysztof,

On 2017-09-11 15:18, Krzysztof Kozlowski wrote:
> On Mon, Sep 11, 2017 at 1:42 PM, Maciej Purski <m.purski at samsung.com> wrote:
>>>> +       ctx->client[I2C_MHL] = client;
>>>> +
>>>> +       ctx->client[I2C_TPI] = i2c_new_dummy(adapter, I2C_TPI_ADDR);
>>>> +       if (!ctx->client[I2C_TPI]) {
>>>> +               dev_err(ctx->dev, "failed to create TPI client\n");
>>>> +               return -ENODEV;
>>>> +       }
>>>> +
>>>> +       ctx->client[I2C_HDMI] = i2c_new_dummy(adapter, I2C_HDMI_ADDR);
>>>> +       if (!ctx->client[I2C_HDMI]) {
>>>> +               dev_err(ctx->dev, "failed to create HDMI RX client\n");
>>>> +               goto fail_tpi;
>>>> +       }
>>>> +
>>>> +       ctx->client[I2C_CBUS] = i2c_new_dummy(adapter, I2C_CBUS_ADDR);
>>>> +       if (!ctx->client[I2C_CBUS]) {
>>>> +               dev_err(ctx->dev, "failed to create CBUS client\n");
>>>> +               goto fail_hdmi;
>>>> +       }
>>> You are using i2c_smbus_* calls. Why not converting to regmap_i2c? It is
>>> preferred interface.
>>
>> According to my search, there are only 5 drivers, which use regmap_i2c and
>> none of them in drm. If you think that it is really needed, could you please
>> explain
>> why?
> There are slightly more than five drivers:
>
> $ git grep regmap_init_i2c | wc -l
> 352
>
> ... and even more using regmap interface in generic (not i2c).
>
> I think this is really wanted because for free you get:
> 1. locking,
> 2. proper locking - with lockdep and nested mutexes :),
> 3. caching of accesses,
> 4. handling of endianness,
> 5. optionally a trivial way of handling interrupts (regmap_irq_chip),
>
> Also this brings unified interface for most of the drivers regardless
> of protocol used beneath (I2C, SPI and even MMIO but for simple cases
> MMIO might not have much sense). This last argument actually brings
> the most benefit for me because it abstracts driver from trivial I2C
> implementation and it could allow even easy code-reuse for e.g. SPI
> version.

Regmap make sense for multi-function chips, which require more than one
client driver (so proper locking is important). It also makes sense if
the chip is produced in more than one flavor (like i2c, spi, MMIO, etc).

None of the above takes place in this case... So in case of this driver
using regmap is IMHO an over-engineering.

 > ...

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland