[PATCH v5 00/11] drivers: PL011: add ARM SBSA Generic UART support

Naresh Bhat nareshgbhat at gmail.com
Fri May 22 06:14:13 PDT 2015

Hi Andre Przywara,

On Thu, May 21, 2015 at 9:56 PM, Andre Przywara <andre.przywara at arm.com> wrote:
> This is the fifth revision of the SBSA UART support series, based on
> the current tty-next branch.
> Beside some minor formatting issues fixed (thanks ot Jakub for
> noticing) the SBSA UART set_termios() function has been reworked.
> We now completely ignore the old value, instead we filter the new
> setting to match the SBSA UART's fixed parameters for word size,
> parity, stop bits and so on.
> This should also address the issues people have seen with ACPI on
> Fedora systems.
> Mark, Naresh, Graeme: can you confirm that this version works for
> you? If needed I can bake a follow-up patch on top of v4.


Yes, I have tested this series on Cavium ThunderX with Fedora21 FS
works fine for me.

Tested-by: Naresh Bhat <nbhat at cavium.com>

> ----
> The ARM Server Base System Architecture[1] document describes a
> generic UART which is a subset of the ARM 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 integrates 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.
> It provides a device tree and an ACPI binding.
> Beside the obvious effect of code sharing reusing most of the PL011
> code has the advantage of not introducing another serial device
> prefix, so it can go with ttyAMA, which seems to be pretty common.
> As changing the baudrate and other communication parameters is not
> specified for the SBSA UART, any userland attempt will be denied by
> the kernel. The device-tree provided fixed baud rate will be
> reported, so stty for instance prints the right value.
> This series is based on Greg's tty-next branch, a git repo can
> be found at [2] (branch sbsa-uart/v5).
> Patch 1/11 contains a bug fix which applies to the PL011 part also,
> it should be considered regardless of the rest of the series.
> According to Russell this is still racy, but still better than the
> current solution.
> Patch 2-7 refactor some PL011 functions by splitting them up into
> smaller pieces, so that most of 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. Also the new
> device tree binding is documented.
> Patch 11 adds the necessary ACPI boilerplate.
> For testing you should be able to take any hardware which has a PL011
> and change the DT to use a "arm,sbsa-uart" compatible string and the
> baud rate with the "current-speed" property.
> Of course testing with a real SBSA Generic UART is welcomed - as well
> as regression testing with any PL011 implementation.
> I tested this on a FastModel, a Juno and a Midway machine, both in
> PL011 and in (DT-emulated) SBSA mode.
> Tested-by: Robert Richter <rrichter at cavium.com>
> Tested-by: Lorenzo Pieralisi <lorenzo.pieralisi at arm.com>
> Tested-by: Hanjun Guo <hanjun.guo at linaro.org>
> Changelog:
> v4 .. v5:
> - fixed checkpatch --strict complaints
> - rework set_termios:
>   - disallow changes or UART fixed communication parameters
>   - ignore old value to fix an issue with Fedora on ACPI
> v3 .. v4:
> - fixed rebase artifact
> - moved memory allocation out of pl011_allocate_port() function
>   (and consequently renamed that to pl011_find_free_port)
> - added ACPI driver binding
> v2 .. v3:
> - rebased on top of tty-next and Dave's latest PL011 rework
> - fixed module build
> - removed redundant =NULL members in sbsa_uart_ops
> v1 .. v2:
> - rebased on top of 4.0-rc1 and Dave's newest PL011 fix [3]
> - added mandatory current-speed property and report that to userland
> Cheers,
> Andre
> [1] ARM-DEN-0029 Server Base System Architecture, available (click-
>     thru...) from http://infocenter.arm.com
> [2] http://www.linux-arm.org/git?p=linux-ap.git
>     git://linux-arm.org/linux-ap.git
> [3] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-March/327631.html
> 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
> Graeme Gregory (1):
>   drivers: PL011: add ACPI probing for SBSA UART
>  .../devicetree/bindings/serial/arm_sbsa_uart.txt   |  10 +
>  drivers/tty/serial/amba-pl011.c                    | 550 +++++++++++++++------
>  2 files changed, 412 insertions(+), 148 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/serial/arm_sbsa_uart.txt
> --
> 2.3.5

"For things to change, we must change"
-Naresh Bhat

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