Re: [PATCH v2 1/2] dt-bindings: Document the STM32 QSPI bindings

[Ludovic BARRE]

On 04/04/2017 02:20 PM, Rob Herring wrote:
> On Tue, Apr 4, 2017 at 2:28 AM, Ludovic BARRE <ludovic.barre@xxxxxx> wrote:
> > Hi Rob
> >
> > thanks for review
> > my comments below
> >
> > br
> > Ludo
> >
> > On 04/03/2017 06:57 PM, Rob Herring wrote:
> > > On Fri, Mar 31, 2017 at 07:02:03PM +0200, Ludovic Barre wrote:
> > > > From: Ludovic Barre <ludovic.barre@xxxxxx>
> > > >
> > > > This patch adds documentation of device tree bindings for the STM32
> > > > QSPI controller.
> > > >
> > > > Signed-off-by: Ludovic Barre <ludovic.barre@xxxxxx>
> > > > ---
> > > >    .../devicetree/bindings/mtd/stm32-quadspi.txt      | 45
> > > > ++++++++++++++++++++++
> > > >    1 file changed, 45 insertions(+)
> > > >    create mode 100644
> > > > Documentation/devicetree/bindings/mtd/stm32-quadspi.txt
> > > >
> > > > diff --git a/Documentation/devicetree/bindings/mtd/stm32-quadspi.txt
> > > > b/Documentation/devicetree/bindings/mtd/stm32-quadspi.txt
> > > > new file mode 100644
> > > > index 0000000..95a8ebd
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/mtd/stm32-quadspi.txt
> > > > @@ -0,0 +1,45 @@
> > > > +* STMicroelectronics Quad Serial Peripheral Interface(QuadSPI)
> > > > +
> > > > +Required properties:
> > > > +- compatible: should be "st,stm32f469-qspi"
> > > > +- reg: contains the register location and length.
> > > > +  (optional) the memory mapping address and length
> > > Why optional? Either the h/w has it or doesn't. If some chips don't,
> > > they should have a different compatible string.
> > in fact, the stm32 qspi controller can operate in any of the following
> > modes:
> > -indirect mode: all the operations are performed using the qspi registers
> > with read/write.
> > -read memory-mapped mode: the external Flash memory is mapped to the
> >   microcontroller address space and is seen by the system as if it was
> >   an internal memory (use memcpy_fromio). this mode improve read throughput
> >
> > if qspi_mm is defined the qspi controller use read memory-mapped mode
> > else the controller transfers in indirect mode.
> You should always have the memory region defined because that's what
> the h/w has. If you want another property to select the mode, then
> perhaps that's fine. But why? Can't the OS figure out which to use?
> Why would you ever not use memory mapped mode unless the driver
> doesn't yet support it?
ok, I always map the memory region (qspi_mm is now required).
if the nor-flash is more bigger than "qspi memory region", I force to use
the indirect mode.
> Rob