Hi Alexandre, On Tue, Sep 11, 2018 at 8:58 PM Alexandre Belloni <alexandre.belloni@xxxxxxxxxxx> wrote: > On 11/09/2018 19:39:30+0100, Lee Jones wrote: > > On Tue, 11 Sep 2018, Geert Uytterhoeven wrote: > > > > > On Tue, Sep 11, 2018 at 5:36 PM Alexandre Belloni > > > <alexandre.belloni@xxxxxxxxxxx> wrote: > > > > On 11/09/2018 16:59:09+0200, Geert Uytterhoeven wrote: > > > > > On Tue, Sep 11, 2018 at 11:40 AM Alexandre Belloni > > > > > <alexandre.belloni@xxxxxxxxxxx> wrote: > > > > > > Then you'd have multiple compatible strings for the same IP which is a > > > > > > big no-no. > > > > > > > > > > It's still the same hardware device, isn't? > > > > > What if the SPI or UART slave is not on-board, but on an expansion board? > > > > > Then the SoC-specific .dtsi has no idea what mode should be used. > > > > > > > > > > Hence shouldn't the software derive the hardware mode from the full > > > > > hardware description in DT? If that's impossible (I didn't look into detail > > > > > whether an SPI bus can easily be distinguished from a UART bus), perhaps > > > > > a mode property should be added? > > > > > > > > Yes, this is exactly what is done: > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/lee/mfd.git/tree/drivers/mfd/at91-usart.c?h=ib-mfd-spi-tty-4.20-1#n33 > > > > > > OK. > > > > > > I guess the main "hackish" part is that the mfd_cell uses of_compatible, > > > which thus requires having additional compatible values? > > > > > > I think those can just be removed. AFAICS, the SPI and serial drivers already > > > match against the "at91_usart_spi" resp. "atmel_usart_serial" platform device > > > names? > > > > The hackish part of this driver is that it's using MFD for something > > which is clearly not an MFD. It's a USART device. Nothing more, > > nothing less. > > > > Does anyone have the datasheet to hand? > > It is not a simple usart, it is either a usart or a full blown SPI > controller with registers changing layout depending on the selected > mode. Otherwise, I'm not sure how you would get a USART to do SPI. Note the "S" in USART. SPI is just synchronous serial with a shared clock for transmit and receive. So the hardware is not that unrelated. 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
