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?
Thanks, Miquèl