Hi Laurent,
Thank you for the review comments.
> On Tuesday 18 Oct 2016 16:29:24 Geert Uytterhoeven wrote:
> > On Wed, Oct 12, 2016 at 4:10 PM, Ramesh Shanmugasundaram wrote:
> > > This patch adds Digital Radio Interface (DRIF) support to R-Car Gen3
> SoCs.
> > > The driver exposes each instance of DRIF as a V4L2 SDR device. A
> > > DRIF device represents a channel and each channel can have one or
> > > two sub-channels respectively depending on the target board.
> > >
> > > DRIF supports only Rx functionality. It receives samples from a RF
> > > frontend tuner chip it is interfaced with. The combination of DRIF
> > > and the tuner device, which is registered as a sub-device,
> > > determines the receive sample rate and format.
> > >
> > > In order to be compliant as a V4L2 SDR device, DRIF needs to bind
> > > with the tuner device, which can be provided by a third party
> > > vendor. DRIF acts as a slave device and the tuner device acts as a
> > > master transmitting the samples. The driver allows asynchronous
> > > binding of a tuner device that is registered as a v4l2 sub-device.
> > > The driver can learn about the tuner it is interfaced with based on
> > > port endpoint properties of the device in device tree. The V4L2 SDR
> > > device inherits the controls exposed by the tuner device.
> > >
> > > The device can also be configured to use either one or both of the
> > > data pins at runtime based on the master (tuner) configuration.
> >
> > Thanks for your patch!
> >
> > > --- /dev/null
> > > +++ b/Documentation/devicetree/bindings/media/renesas,drif.txt
> > > @@ -0,0 +1,109 @@
> > > +Renesas R-Car Gen3 DRIF controller (DRIF)
> > > +-----------------------------------------
> > > +
> > > +Required properties:
> > > +--------------------
> > > +- compatible: "renesas,drif-r8a7795" if DRIF controller is a part
> > > +of
> > > R8A7795 SoC.
> >
> > "renesas,r8a7795-drif", as Rob already pointed out.
> >
> > > + "renesas,rcar-gen3-drif" for a generic R-Car Gen3
> > > + compatible
> > > device.
> > > + When compatible with the generic version, nodes must
> > > + list
> > > the
> > > + SoC-specific version corresponding to the platform first
> > > + followed by the generic version.
> > > +
> > > +- reg: offset and length of each sub-channel.
> > > +- interrupts: associated with each sub-channel.
> > > +- clocks: phandles and clock specifiers for each sub-channel.
> > > +- clock-names: clock input name strings: "fck0", "fck1".
> > > +- pinctrl-0: pin control group to be used for this controller.
> > > +- pinctrl-names: must be "default".
> > > +- dmas: phandles to the DMA channels for each sub-channel.
> > > +- dma-names: names for the DMA channels: "rx0", "rx1".
> > > +
> > > +Required child nodes:
> > > +---------------------
> > > +- Each DRIF channel can have one or both of the sub-channels
> > > +enabled in a
> > > + setup. The sub-channels are represented as a child node. The name
> > > +of
> > > the
> > > + child nodes are "sub-channel0" and "sub-channel1" respectively.
> > > + Each
> > > child
> > > + node supports the "status" property only, which is used to
> > > enable/disable
> > > + the respective sub-channel.
> > >
> > > +Example
> > > +--------
> > > +
> > > +SoC common dtsi file
> > > +
> > > +drif0: rif@e6f40000 {
> > > + compatible = "renesas,drif-r8a7795",
> > > + "renesas,rcar-gen3-drif";
> > > + reg = <0 0xe6f40000 0 0x64>, <0 0xe6f50000 0 0x64>;
> > > + interrupts = <GIC_SPI 12 IRQ_TYPE_LEVEL_HIGH>,
> > > + <GIC_SPI 13 IRQ_TYPE_LEVEL_HIGH>;
> > > + clocks = <&cpg CPG_MOD 515>, <&cpg CPG_MOD 514>;
> > > + clock-names = "fck0", "fck1";
> > > + dmas = <&dmac1 0x20>, <&dmac1 0x22>;
> > > + dma-names = "rx0", "rx1";
> >
> > I could not find the DMAC channels in the datasheet?
> > Most modules are either tied to dmac0, or two both dmac1 and dmac2.
> > In the latter case, you want to list two sets of dmas, one for each
> DMAC.
> >
> > > + power-domains = <&sysc R8A7795_PD_ALWAYS_ON>;
> > > + status = "disabled";
> > > +
> > > + sub-channel0 {
> > > + status = "disabled";
> > > + };
> > > +
> > > + sub-channel1 {
> > > + status = "disabled";
> > > + };
> > > +
> > > +};
> >
> > As you're modelling this in DT under a single device node, this means
> > you cannot use runtime PM to manage the module clocks of the
> > individual channels.
> >
> > An alternative could be to have two separate nodes for each channel,
> > and tie them together using a phandle.
>
> A quick glance at the documentation shows no dependency between the two
> channels at a software level. They both share the same clock and
> synchronization input pins, but from a hardware point of view that seems
> to be it. It thus looks like we could indeed model the two channels as
> separate nodes, without tying them together.
Thanks & I agree with your suggestion to keep each DRIF sub-channels as
separate node. However, I would still like to tie them as Geert pointed out
because
1) DRIF, as you may know, is a botched MSIOF slave. H/W manual states there are
4 channels each having SCK, WS & two data lines D0 & D1) but in reality each
sub-channel (SCK,WS & Dx) can indeed act alone (they have their own resources)
except that they share SCK & WS as you pointed out. It is not clean design but
it tries to market a radio interface use case - I & Q data from master received
on D0 & D1 and this data is relational. For the master and the end user
application, this internal split is not visible.
2) If you look at PFC, when a DRIF channel is selected using MOD_SEL it enables
both the sub-channels. This shows the intended use case. Ofcourse the
imperfection cannot be hidden - you could still configure one of the D0/D1 pins
as GPIO even after PFC selects them both :-(.
3) Manual states "When setting to registers, it needs to set the same values to
two register sets located per channel" - This driver is doing that by accessing
each sub-channel based on DT setup. This way driver exposes one interface per
channel and provides user the data from two data pins as if it comes from one
device interface.
Thanks,
Ramesh
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