Hi Marek,
On Mon, Jan 9, 2017 at 10:55 PM, Marek Vasut <marek.vasut@xxxxxxxxx> wrote:
> On 01/09/2017 10:02 PM, Lars-Peter Clausen wrote:
>> On 01/09/2017 09:56 PM, Marek Vasut wrote:
>>> On 01/09/2017 09:07 PM, Lars-Peter Clausen wrote:
>>>> On 01/09/2017 02:47 PM, Marek Vasut wrote:
>>>>> On 01/09/2017 02:45 PM, Lars-Peter Clausen wrote:
>>>>>> On 01/09/2017 01:03 AM, Marek Vasut wrote:
>>>>>> [...]
>>>>>>> +- renesas,gyroadc-mode: GyroADC mode of operation, must be either of:
>>>>>>> + 1 - MB88101A mode, 12bit sampling, 4 channels
>>>>>>> + 2 - ADCS7476 mode, 15bit sampling, 8 channels
>>>>>>> + 3 - MAX1162 mode, 16bit sampling, 8 channels
>>>>>>
>>>>>> So is this a ADC, or is this just a specialized SPI controller that
>>>>>> interfaces to an external ADC?
>>>>>
>>>>> It's a special SPI controller, except one cannot access the SPI bus
>>>>> directly. It sends out clock and reads in the data from the ADC .
>>>>
>>>> OK, thanks for the clarification. The commit message does not mention this
>>>> at the moment and makes it sound like this is a built-in ADC.
>>>>
>>>> Also the renesas,gyroadc-mode property is more of a driver configuration
>>>> setting rather than a description of the hardware, at least it is not very
>>>> DT-ish.
>>>>
>>>> I'd go with something like
>>>>
>>>>
>>>> &adc {
>>>> compatible = "renesas,r8a7791-gyroadc";
>>>> ...
>>>>
>>>> adc@0 {
>>>> reg = <0>;
>>>> compatible = "maxim,max1162";
>>>
>>> But then the max1162 ADC driver* will try to bind to this, right ?
>>> And since the MAX1162 is an SPI device, it will fail to work as the
>>> ADC driver does not provide any sort of SPI interface. Or is that
>>> actually OK ?
>>
>> Only if you call of_register_spi_devices().
>>
>> We for example have devices that can either work in SPI or I2C mode and both
>> use the same compatible string. Depending on whether the device is a subnode
>> of a SPI or I2S controller it is registered as a SPI or I2C device.
>>
>> This situation is not that different.
>
> So in this case, the gyroadc driver would instead iterate over the
> subnodes, check the compatible string and configure the channel mode
> according to the subnode compatible string?
That's correct.
> But then, the gyroadc only has one configuration register which applies
> to all channels, which selects how many bits to read from the connected
> SPI-ADC device(s) (sample width). This is not per-channel configurable.
> The driver would then have to check if all the compatible properties in
> the ADC subnodes select the same ADC or at least ADC which has the same
Correct again.
> sample width. This looks like a duplication to me. Thoughts ?
While the protocols have to be the same for each channel, you can connect
different devices. If you have e.g. a thermometer or barimeter that speaks
the same protocol as a max1162 (i.e. it responds with 2 zero bytes and 2
bytes of data), you can mix and match that with max1162 devices, once
you have added support for the thermometer or barimeter to your driver.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
-- Linus Torvalds
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