Hi Jiada, On Mon, Apr 24, 2017 at 2:48 PM, Jiada Wang <jiada_wang@xxxxxxxxxx> wrote: > On 04/24/2017 03:55 AM, Geert Uytterhoeven wrote: >> 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. > > It doesn't need to be a multi-master bus, > for example A is master device for slave device B. > while B has its own slave device C > for each SPI connection A <=> B, and B <=> C, there is only one master > device. > > and I think from use case point of view, it's very normal, > one CPU upon receives command from external SPI master device, > it writes data to its own slave device (EEPROM) connected to it. So "A <=> B" and "B <=> C" are two distinct SPI buses? Or do they share some signals? Your comment seems to suggest otherwise: > > > 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 they are distinct, it should work. Then B has two SPI controllers: one slave controller controlled by A, and one master controller to control C. 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 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html