Re: Add stacked and parallel memories support in spi-nor

10 Oct 2024

      Hi Amit,
amit.kumar-mahapatra@amd.com wrote on Thu, 10 Oct 2024 10:35:06 +0000:
...
Hello Miquel,
...
-----Original Message-----
From: Miquel Raynal miquel.raynal@bootlin.com
Sent: Thursday, October 10, 2024 2:58 PM
To: Mahapatra, Amit Kumar amit.kumar-mahapatra@amd.com
Cc: Tudor Ambarus tudor.ambarus@linaro.org; michael@walle.cc;
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Subject: Re: Add stacked and parallel memories support in spi-nor
Hi Amit,
amit.kumar-mahapatra@amd.com wrote on Thu, 10 Oct 2024 09:17:58 +0000:
...
Hello Miquel,
...
...

The stacked-memories DT bindings will contain the phandles of

the flash nodes
connected in stacked mode.
...

The first flash node will contain the mtd partition that would

have the cross over memory staring at a memory location in the
first flash and ending at some memory location of the 2nd flash
I don't like that much. Describing partitions past the actual device
sounds wrong. If you look into [1] there is a suggestion from Rob to
handle this case using a property that tells us there is a
continuation, so from a software perspective we can easily make the link, but on
the hardware description side the information are correct.
...
I reviewed Rob's suggestions in [1], and I need to examine the MTD
layer to determine how this can be implemented from a software perspective.
For reference, here is Rob's suggestion:
Describe each device and partition separately and add link(s) from one
partition to the next
flash0 {
  partitions {
    compatible = "fixed-partitions";
    concat-partition = <&flash1_partitions>;
    ...
  };
};
flash1 {
  flash1_partition: partitions {
    compatible = "fixed-partitions";
    ...
  };
};
...
If this description is accepted, then fine, you can deprecate the "stacked-
memories"
...
...
property.
I believe that in addition to Rob's description, we should also
include the 'stacked-memories' property. This property helps us
identify which flashes are stacked, while Rob's suggestion explains
how the partitions within the stacked flashes are connected.
For example, if we have three flashes connected to an SPI host, with
flash@0 and flash@1 operating in stacked mode and flash@2 functioning
as a standalone flash, the Device Tree binding might look something like this:
Please share your thoughts on this.
spi@0 {
  ...
  flash@0 {
    compatible = "jedec,spi-nor"
    reg = <0x00>;
    stacked-memories = <&flash@0 &flash@1>;
    spi-max-frequency = <50000000>;
    ...
        flash0_partition: partitions {
            compatible = "fixed-partitions";
   concat-partition = <&flash1_partitions>;
        	partition@0 {
          	    label = "Stacked-Flash-1";
                reg = <0x0 0x800000>;
   }
        }
    }
  flash@1 {
    compatible = "jedec,spi-nor"
     reg = <0x01>;
    spi-max-frequency = <50000000>;
    ...
        flash1_partition: partitions {
            compatible = "fixed-partitions";
   concat-partition = <&flash0_partitions>;
        	partition@0 {
          	    label = " Stacked-Flash-2";
                reg = <0x0 0x800000>;
   }
        }
  }
flash@2 {
    compatible = "jedec,spi-nor"
     reg = <0x01>;
    spi-max-frequency = <50000000>;
    ...
        partitions {
            compatible = "fixed-partitions";
   concat-partition = <&flash0_partitions>;
        	partition@0 {
          	    label = "Single-Flash";
                reg = <0x0 0x800000>;
   }
        }
  }
I'm sorry but this is pretty messed up. The alignments are wrong, I believe the labels
are wrong, the reg properties as well. Can you please work on this example and
send an updated version?
Apologies for that. Here's the updated version along with the explanation.
Thanks for the update.
...
spi@0 {
   ...
   flash@0 {
   	compatible = "jedec,spi-nor"
    		reg = <0x00>;
    		stacked-memories = <&flash@0 &flash@1>;
The same property should, IMHO, also be expected...
...
		spi-max-frequency = <50000000>;
		...
    		partitions {
        		compatible = "fixed-partitions";
    			concat-partition = <&flash1_partition>; /* Link to the flash@1 partition@0 */
            		flash0_partition: partition@0 {
                			label = "part0_0";
            			reg = <0x0 0x800000>;
    			}
    		}
	}

flash@1 {
    		compatible = "jedec,spi-nor"
     		reg = <0x01>;
... here.
...
		spi-max-frequency = <50000000>;
		...
    		partitions {
        		compatible = "fixed-partitions";
    			concat-partition = <&flash0_partition>; /* Link to the flash@0 partition@0 */
            		flash1_partition: partition@0 {
                			label = "part0_1";
            			reg = <0x0 0x800000>;
    			}
    		}

}
flash@2 {
    		compatible = "jedec,spi-nor"
     		reg = <0x02>;
    		spi-max-frequency = <50000000>;
    		...
        		partitions {
            		compatible = "fixed-partitions";       
                		partition@0 {
                    			label = "part1_0";
                			reg = <0x0 0x800000>;
        			}
        		}
   }
}
Otherwise, okay for me.
Thanks,
Miquèl