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

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

Hello Miquel,

> -----Original Message-----
> From: Miquel Raynal <miquel.raynal@xxxxxxxxxxx>
> Sent: Thursday, October 10, 2024 2:58 PM
> To: Mahapatra, Amit Kumar <amit.kumar-mahapatra@xxxxxxx>
> Cc: Tudor Ambarus <tudor.ambarus@xxxxxxxxxx>; michael@xxxxxxxx;
> broonie@xxxxxxxxxx; pratyush@xxxxxxxxxx; richard@xxxxxx; vigneshr@xxxxxx; Rob
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> nicolas.ferre@xxxxxxxxxxxxx; alexandre.belloni@xxxxxxxxxxx;
> claudiu.beznea@xxxxxxxxx; Simek, Michal <michal.simek@xxxxxxx>; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; alsa-devel@xxxxxxxxxxxxxxxx;
> patches@xxxxxxxxxxxxxxxxxxxxx; linux-sound@xxxxxxxxxxxxxxx; git (AMD-Xilinx)
> <git@xxxxxxx>; amitrkcian2002@xxxxxxxxx; Conor Dooley
> <conor.dooley@xxxxxxxxxxxxx>; beanhuo@xxxxxxxxxx
> Subject: Re: Add stacked and parallel memories support in spi-nor
> 
> Hi Amit,
> 
> amit.kumar-mahapatra@xxxxxxx 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.

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. 
I also need to examine the MTD layer to determine how Rob's suggestion 
can be implemented from a software perspective.

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>;
    		...
        		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>;
    		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>;
        			}
        		}
  	}
}

Regards,
Amit
> 
> Thanks,
> Miquèl