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SubjectRe: [PATCH 2/4] msm_serial: Add devicetree support
On Sat, Aug 13, 2011 at 11:34:15PM +0200, Arnd Bergmann wrote:
> On Saturday 13 August 2011 12:46:45 David Brown wrote:
> >
> > I'm not sure actually what is best to use here. I'm thinking that the
> > 'lite' identifier should perhaps go away. MSM's have two UARTS on
> > them, an older "simple" PIO type of UART, and a newer one that can do
> > DMA (called the hsuart for high-speed). The hsuart can also be used
> > in a non-DMA driver in a mostly compatible way with the old UART.
> >
> > For non-high-speed applications, the user will probably just want to
> > use the non-DMA driver. My question is then: if the device tree
> > describes it as
> >
> > compatible = "qcom,msm-hsuart", "qcom,msm-uart";
> >
> > and one driver matches qcom,msm-hsuart and another matches
> > qcom,msm-uart, which driver will get used. Ideally, it would use the
> > earliest one in the list.
> >
> > If that's the case, I'll get rid of the -lite suffix and just make the
> > non-DMA driver compatible with the plain "qcom,msm-uart".
> I believe that unfortunately the answer is that the first driver that
> matches anything will get used. There are two possible ways that I can
> see to make it do what you want anyway:
> 1. In the probe function for the slow driver, you return an error
> when the device you get passed matches "qcom,msm-hsuart", possibly
> dependent on whether the other driver also got built.
> 2. You register one platform driver that handles both names and
> gives the device to just one of the two drivers. This would probably
> require linking the two drivers into the same module, or having
> the non-DMA speed driver just act as a library.

How about if I just keep it simple for now. Since there isn't
actually a driver for the DMA version, this driver will handle both
UART blocks, so I'll just do the plain thing in the DT.

In the future, when a DMA-capable driver exists, we can figure out how
to determine which driver should be used. At this point, I'm not even
sure what the correct answer will be, since a given configuration may
want to use non-DMA for one msm-hsuart device, and the DMA driver for
another. It's kind of board/use specific, but beyond just describing
what the hardware is.

I've just sent new patches with this fixed up.


Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.

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