Re: [PATCH 4/4] arm64: dts: qcom: sc8280xp: add missing spi nodes

[Brian Masney <bmasney@redhat.com>]

+ Mark Brown and linux-spi list

On Tue, Dec 13, 2022 at 12:46:18PM +0530, Shazad Hussain wrote:
> On 12/12/2022 11:53 PM, Brian Masney wrote:
> > Add the missing nodes for the spi buses that's present on this SoC.
> > 
> > This work was derived from various patches that Qualcomm delivered
> > to Red Hat in a downstream kernel.
> > 
> > Signed-off-by: Brian Masney <bmasney@redhat.com>
> > ---
> >   arch/arm64/boot/dts/qcom/sc8280xp.dtsi | 384 +++++++++++++++++++++++++
> >   1 file changed, 384 insertions(+)
> > 
> > diff --git a/arch/arm64/boot/dts/qcom/sc8280xp.dtsi b/arch/arm64/boot/dts/qcom/sc8280xp.dtsi
> > index 392a1509f0be..b50db09feae2 100644
> > --- a/arch/arm64/boot/dts/qcom/sc8280xp.dtsi
> > +++ b/arch/arm64/boot/dts/qcom/sc8280xp.dtsi
> > @@ -829,6 +829,22 @@ qup2_i2c16: i2c@880000 {
> >   				status = "disabled";
> >   			};
> > +			qup2_spi16: spi@880000 {
> > +				compatible = "qcom,geni-spi";
> > +				reg = <0 0x00880000 0 0x4000>;
> > +				clocks = <&gcc GCC_QUPV3_WRAP2_S0_CLK>;
> > +				clock-names = "se";
> > +				interrupts = <GIC_SPI 373 IRQ_TYPE_LEVEL_HIGH>;
> > +				#address-cells = <1>;
> > +				#size-cells = <0>;
> > +				interconnects = <&clk_virt MASTER_QUP_CORE_2 0 &clk_virt SLAVE_QUP_CORE_2 0>,
> > +				                <&gem_noc MASTER_APPSS_PROC 0 &config_noc SLAVE_QUP_2 0>,
> > +				                <&aggre1_noc MASTER_QUP_2 0 &mc_virt SLAVE_EBI1 0>;
> > +				interconnect-names = "qup-core", "qup-config", "qup-memory";
> > +				spi-max-frequency = <50000000>;
> 
> This is device property not host and same applicable for all below spi
> nodes.
> Also FYI let's enable below SPI for Qdrive usecases once spidev compatible
> name is confirmed.
> SE9  0x00A84000
> SE22 0x00898000

I talked to Javier Martinez Canillas yesterday about the spidev driver
and I think I now have a better understanding of what we need to do.
Quick background for Mark. For this automotive program, Qualcomm will be
delivering to Red Hat and our customers parts of the media stack in
userspace. This will be closed source, proprietary code that parts of it
will need to interface with SPI.

We can't add a generic qcom,spidev compatible to the spidev driver since
this is just a software abstraction. Instead, each type of device will
need to have it's own compatible that uniquely describes the type of
device. So you might have a compatible like qcom,spi-video-codec. There
will need to be a DT binding added that describes the hardware. I suspect
that a SPI device can simply be added to trivial-devices.yaml. Once the
DT binding is accepted, the compatible can be added to the spidev.c
driver. If an in-kernel driver is written in the future, then the 
compatible can be moved from spidev to the new driver.

Mark: Is my understanding above correct? If so, will it be a problem to
get a compatible added to spidev.c if the corresponding userspace code is
closed source and proprietary?

Brian