Re: [PATCH v2 4/6] tty: serial: msm: Add TX DMA support

["Ivan T. Ivanov" <ivan.ivanov@linaro.org>]

On Wed, 2015-09-30 at 14:29 +0100, Mark Rutland wrote:
> On Wed, Sep 30, 2015 at 01:08:24PM +0100, Ivan T. Ivanov wrote:
> > Add transmit DMA support for UARTDM type of controllers.
> > 
> > Tested on APQ8064, which have UARTDM v1.3 and ADM DMA engine
> > and APQ8016, which have UARTDM v1.4 and BAM DMA engine.
> > 
> > Signed-off-by: Ivan T. Ivanov ivanov@linaro.org>
> > ---
> >  .../devicetree/bindings/serial/qcom,msm-uartdm.txt |   3 +
> >  drivers/tty/serial/msm_serial.c                    | 312 +++++++++++++++++++--
> >  drivers/tty/serial/msm_serial.h                    |   3 +
> >  3 files changed, 294 insertions(+), 24 deletions(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/serial/qcom,msm-uartdm.txt b/Documentation/devicetree/bindings/serial/qcom,msm-uartdm.txt
> > index a2114c217376..a600023d9ec1 100644
> > --- a/Documentation/devicetree/bindings/serial/qcom,msm-uartdm.txt
> > +++ b/Documentation/devicetree/bindings/serial/qcom,msm-uartdm.txt
> > @@ -26,6 +26,9 @@ Required properties:
> >  Optional properties:
> >  - dmas: Should contain dma specifiers for transmit and receive channels
> >  - dma-names: Should contain "tx" for transmit and "rx" for receive channels
> > +- qcom,tx-crci: Identificator <u32> for Client Rate Control Interface to be
> > +           used with TX DMA channel. Required when using DMA for transmission
> > +           with UARTDM v1.3 and bellow.
> 
> This sounds like it belongs in the dma-specifier, and dealt with by the
> DMA controller driver.
> 
> Why does the UART driver need to know about this?

CRCI information was part of the first version of ADM DMA engine driver
bindings, but Andy remove it because some client devices are requiring
more that one CRCI number. See here[1] and here [2].

Regards,
Ivan

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2015-January/314190.html
[2] https://lkml.org/lkml/2015/8/19/19