RE: [RFC PATCH 2/2] dt-bindings: spi: Update stacked and parallel bindings

["Mahapatra, Amit Kumar" <amit.kumar-mahapatra@xxxxxxx>]

Hello Miquel,

> >         flash@1 {
> >                 compatible = "jedec,spi-nor"
> >                 reg = <0x01>;
> >                 stacked-memories = <&flash@0 &flash@1>;
> >                 spi-max-frequency = <50000000>;
> >                 ...
> >                         partitions {
> 
> Same comment as before here.

Sorry again 

spi@0 {
	...
	flash@0 {
		compatible = "jedec,spi-nor"
		reg = <0x00>;
		stacked-memories = <&flash@0 &flash@1>;
		spi-max-frequency = <50000000>;
		...
		partitions {
			compatible = "fixed-partitions";
			concat-partition = <&flash0_part0 &flash1_part0>;
			
			flash0_part0: partition@0 {
				label = "part0_0";
				reg = <0x0 0x800000>;
			};
		};
	};
	flash@1 {
		compatible = "jedec,spi-nor"
		reg = <0x01>;
		stacked-memories = <&flash@0 &flash@1>;
		spi-max-frequency = <50000000>;
		...
		partitions {
			compatible = "fixed-partitions";
			concat-partition = <&flash0_part0 &flash1_part0>;
			
			flash1_part0: partition@0 {
				label = "part0_1";
				reg = <0x0 0x800000>;
			};
		};
	};
};

> 
> >                         compatible = "fixed-partitions";
> >                                 concat-partition = <&flash0_partition &flash1_partition>;
> >                                 flash1_partition: partition@0 {
> >                                         label = "part0_1";
> >                                         reg = <0x0 0x800000>;
> >                                 }
> >                         }
> >         }
> >
> > }
> >
> > parallel-memories binding changes:
> > - Remove the size information from the bindings and change the type to
> >   boolen.
> > - Each flash connected in parallel mode should be identical and will have
> >   one flash node for both the flash devices.
> > - The “reg” prop will contain the physical CS number for both the connected
> >   flashes.
> >
> > The new layer will double the mtd-> size and register it with the mtd
> > layer.
> 
> Not so sure about that, you'll need a new mtd device to capture the whole device.
> But this is implementation related, not relevant for binding.
> 
> >
> > spi@1 {
> >         ...
> >         flash@3 {
> >                 compatible = "jedec,spi-nor"
> >                 reg = <0x00 0x01>;
> >                 paralle-memories ;
> 
> Please fix the typos and the spacing (same above).
> 
> >                 spi-max-frequency = <50000000>;
> >                 ...
> >                         partitions {
> >                         compatible = "fixed-partitions";
> >                                 flash0_partition: partition@0 {
> >                                         label = "part0_0";
> >                                         reg = <0x0 0x800000>;
> >                                 }
> >                         }
> >         }
> > }
> >
> > Signed-off-by: Amit Kumar Mahapatra <amit.kumar-mahapatra@xxxxxxx>
> > ---
> >  .../bindings/spi/spi-controller.yaml          | 23 +++++++++++++++++--
> >  .../bindings/spi/spi-peripheral-props.yaml    |  9 +++-----
> >  2 files changed, 24 insertions(+), 8 deletions(-)
> >
> > diff --git a/Documentation/devicetree/bindings/spi/spi-controller.yaml
> > b/Documentation/devicetree/bindings/spi/spi-controller.yaml
> > index 093150c0cb87..2d300f98dd72 100644
> > --- a/Documentation/devicetree/bindings/spi/spi-controller.yaml
> > +++ b/Documentation/devicetree/bindings/spi/spi-controller.yaml
> > @@ -185,7 +185,26 @@ examples:
> >          flash@2 {
> >              compatible = "jedec,spi-nor";
> >              spi-max-frequency = <50000000>;
> > -            reg = <2>, <3>;
> > -            stacked-memories = /bits/ 64 <0x10000000 0x10000000>;
> > +            reg = <2>;
> > +            stacked-memories = <&flash0 &flash1>;
> >          };
> 
> I'm sorry but this is not what you've talked about in this series.
> Either you have flash0 and flash1 and use the stacked-memories property in both of
> them (which is what you described) or you create a third virtual device which points
> to two other flashes. This example allows for an easier use of the partitions

If I understand your point correctly, you're suggesting that we should 
avoid using stacked-memories and concat-partition properties together and 
instead choose one approach. Between the two, I believe concat-partition 
would be the better option.

While looking into your mtdconcat patch [1], I noticed that it creates a 
virtual MTD device that points to partitions on two different flash nodes, 
which aligns perfectly with our requirements.

However, there are two key concerns that, if addressed, could make this 
patch suitable for the stacked mode:

1/ The creation of a virtual device that does not have a physical 
existence.

2/ The creation of individual MTD devices that are concatenated to form 
the virtual MTD device, which may not be needed by the user.

Regarding the first point, I currently cannot think of a better generic 
way to support the stacked feature than creating a virtual device.
Please let me know you thoughts on this.

For the second point, one possible solution is to hide the individual MTD 
devices (that form the concatenated virtual MTD device) from the user once 
the virtual device is created. Please let us know if you have any other 
suggestions to address this issue.

[1] https://lore.kernel.org/linux-mtd/20191127105522.31445-5-miquel.raynal@xxxxxxxxxxx/ 

Regards,
Amit

> mechanism on top of a virtual mtd device but, heh, you're now describing a virtual
> mtd device, which is not a physical device as it "should" be.
> 
> Thanks,
> Miquèl