On Fri, Sep 19, 2014 at 01:21:13PM +0100, Andre Przywara wrote: > (This version has still issues, but I'd like to have feedback on > the general feasibility of this approach before wasting even more > time on debugging). > > The ARM Server Base System Architecture[1] document describes a > generic UART which is a subset of the PL011 UART. > It lacks DMA support, baud rate control and modem status line > control, among other things. > The idea is to move the UART initialization and setup into the > firmware (which does this job today already) and let the kernel just > use the UART for sending and receiving characters. > > This patchset is an attempt to integrate support for this UART subset > into the existing PL011 driver - basically by refactoring some > functions and providing a new uart_ops structure for it. It also has > a separate probe function to be not dependent on AMBA/PrimeCell. > Beside the obvious effect of code sharing it has the advantage of not > introducing another serial device prefix, so it can go with ttyAMA, > which seems to be pretty common. > > There is still one issue in bringing up the UART. On the PL011 we > send a dummy character via the loopback facility with the FIFOs > disabled to get things going, but both FIFO control and loopback are > outside of the SBSA spec. I consider this loopback approach a kludge > anyway, but am struggling to find a better way of fixing this due to > my lack of understanding of the TTY/serial layer. > If someone with more wisdom could enlighten me, I would be grateful. > This is the killer issue at the moment it seems, once we get to usespace the tty does not work. > > Patch 1/10 contains a bug fix which applies to the PL011 part also, > it should be considered regardless of the rest of the series. > Patch 2-7 refactor some PL011 functions by splitting them up into > smaller pieces, so that most the code can be reused later by the SBSA > part. > Patch 8 and 9 introduce two new properties for the vendor structure, > this is for SBSA functionality which cannot be controlled by > separate uart_ops members only. > Patch 10 then finally drops in the SBSA specific code, by providing > a new uart_ops, vendor struct and probe function for it. > > Please have a look and tell me whether this SBSA driver approach has > any future. > The patch series looks reasonable to me based on my very limited knowledge of the tty layer and the pl011 UART. Graeme > Regards, > Andre > > Andre Przywara (10): > drivers: PL011: avoid potential unregister_driver call > drivers: PL011: refactor pl011_startup() > drivers: PL011: refactor pl011_shutdown() > drivers: PL011: refactor pl011_set_termios() > drivers: PL011: refactor pl011_probe() > drivers: PL011: replace UART_MIS reading with _RIS & _IMSC > drivers: PL011: move cts_event workaround into separate function > drivers: PL011: allow avoiding UART enabling/disabling > drivers: PL011: allow to supply fixed option string > drivers: PL011: add support for the ARM SBSA generic UART > > .../devicetree/bindings/serial/arm_sbsa_uart.txt | 9 + > drivers/tty/serial/amba-pl011.c | 509 ++++++++++++++------ > 2 files changed, 380 insertions(+), 138 deletions(-) > create mode 100644 Documentation/devicetree/bindings/serial/arm_sbsa_uart.txt > > -- > 1.7.9.5 > > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
