Re: [PATCH RFC 0/5] *** SPI Slave mode support ***

[Geert Uytterhoeven]

Hi Jiada,

On Fri, Apr 14, 2017 at 7:39 AM, Jiada Wang <jiada_wang@xxxxxxxxxx> wrote:
> On 04/13/2017 12:47 PM, Geert Uytterhoeven wrote:
>> On Thu, Apr 13, 2017 at 2:59 PM, Mark Brown<broonie@xxxxxxxxxx>  wrote:
>>> On Thu, Apr 13, 2017 at 05:13:59AM -0700, jiada_wang@xxxxxxxxxx wrote:
>>>> From: Jiada Wang<jiada_wang@xxxxxxxxxx>
>>>>
>>>> v1:
>>>>    add Slave mode support in SPI core
>>>>    spidev create slave device when SPI controller work in slave mode
>>>>    spi-imx support to work in slave mode
>>>
>>> Adding Geert who also had a series doing this in progress that was
>>> getting very near to being merged.
>>
>> Thank you!
>>
>> Actually my plan is to fix the last remaining issues and resubmit for
>> v4.13.
>
> I noticed your patch set for SPI slave support,
> (I am sure you can find out some of the change
> in this patch set is based on your work).
> we have similar requirement to add slave mode support to ecspi IP on imx6
> Soc.
>
> Our use case is to use spidev as an interface to communicate with external
> SPI master devices.
> meanwhile the SPI bus controller can also act as master device to send data
> to other
> SPI slave devices on the board.

That sounds a bit hackish to me. SPI was never meant to be a multi-master bus.
While it can be done, you will need external synchronization (signals) to
avoid conflicts between the SPI masters.

> I found in your implementation, SPI bus controller is limited to either work
> in master mode or
> slave mode, is there any reasoning to not configure SPI mode based on SPI
> devices use case?

If you really need both master and slave support, you can use 2 subnodes
in DT, the first representing the master, the second the slave.

Mark, what's your opinion about this?

Thanks!

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