Re: [linux-sunxi] [PATCH 2/3] spidev: Add DT binding example.

[Michal Suchanek]

On 26 April 2015 at 13:56, Martin Sperl <kernel@xxxxxxxxxxxxxxxx> wrote:
>
>> On 26.04.2015, at 13:23, Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
>> I think there is actual a use for just binding spidev as spidev,
>> think e.g. the spi pins on the raspberry pi.
>>
>> How do you deal we suggest with such a situation ?
>
> I actually asked the same question a few days ago on the spi list
> (in thread: "spi: spidev: Warn loudly if instantiated from DT as âspidevâ)
> and the summary was:
>
> You can still do as before, but you have to accept that long
> irritating warning.
>
> Or you patch spidev.c to include your pattern of choice for compatiblity

So the suggestion is to add a compatible string like olimex,uext-slot
to spidev and use that compatible in the DT?

That can certainly be done but adding a new compatible for every board
that has some random pins looks like a needless nuisance to me.
Especially compared to i2c where you can just open the bus so long as
ti is enabled.

>
> Or you implement the following proposal (which needs a volunteer):
>> On 23.04.2015, at 09:42, Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
>>
>> So what you need is a way to handover from generic spidev to a device-specific
>> driver, cfr. what graphics drivers do when the device has been bound to by
>> vesafb or simplefb.
>>
>> Could this be implemented in a generic way in the spi or DT code?
>
> ...
>> On 23.04.2015, at 12:36, Mark Brown <broonie@xxxxxxxxxx> wrote:
>> On Thu, Apr 23, 2015 at 09:45:16AM +0200, Geert Uytterhoeven wrote:
>>
>>> I guess this has been suggested before: the spi core could provide spidev
>>> access to all spi client devices which are not bound by a driver?
>>
>> I don't know if it's been suggested before, certainly nobody did the
>> work to make it happen.  I don't think I have a massive objection in
>> principal.

But how do you know there is a device?

Devices on i2c can be probed. On spi you just transfer random data and
hope it does something useful. Some devices have readable registers
and can be probed in a device-specific way but others are write-only.

So binding spidev is in my view just saying that you are going to
transfer random data from userspace on this bus.

Thanks

Michal
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