[PATCH v11 07/10] mtd: spi-nor: Add stacked memories support in spi-nor

[Tudor Ambarus]

On 12/21/23 06:54, Mahapatra, Amit Kumar wrote:
>> Something else to consider: I see that Micron has a twin quad mode:
>> https://media-www.micron.com/-
>> /media/client/global/documents/products/data-sheet/nor-flash/serial-
>> nor/mt25t/generation-
>> b/mt25t_qljs_l_512_xba_0.pdf?rev=de70b770c5dc4da8b8ead06b57c03500
>>
>> The micron's "Separate Chip-Select and Clock Signals" resembles the AMD's
>> dual parallel 8-bit.
> Yes, I agree.
> 
>> Micron's "Shared Chip-Select and Clock Signals" differs from the AMD's
>> stacked mode, as Micron uses DQ[3:0] and DQ[7:4], whereas AMD considers
>> both as DQ[3:0].
> Yes, correct.

Amit, please help me to assess this. I assume Micron and Microchip is
using the same concepts as AMD uses for the "Dual Parallel 8-bit IO
mode", but they call it "Twin Quad Mode".

I was wrong, the AMD datasheet [1] was misleading [2], it described the
IOs for both flashes as IO[3:0], but later on in the "Table QSPI
Interface Signals" the second flash is described with IO[7:4].

The AMD's 8-bit Dual Flash Parallel Interface is using dedicated CS# and
CLK# lines for each flash. As Micron does, isn't it?

Micron says [3] that:
"The device contains two quad I/O die, each able to operate
independently for a total of eight I/Os. The memory map applies to each
die. Each die has internal registers for status, configuration, and
device protection that can be set and read independently from one other.
Micron recommends that internal configuration settings for the two die
be set identically."

it also says that:
"When using quad commands in XIO-SPI or when using QIO-SPI,
DQ[3:0]/DQ[7:4] are I/O."

So I guess the upper layers just ask for a chunk of memory to be written
and the controller handles the cs# lines automatically. How is the AMD
controller working, do you have to drive the cs# lines manually, or you
just set the parallel mode and the controller takes care of everything?

I assume this is how mchp is handling things, they seem to just set a
bit the protocol into the QSPI_IFR.PROTTYP register field and that's all
[4]. They even seem to write the registers of both flashes at the same time.

In what regards the AMD's "dual stack interface", AMD is sharing the
clock and IO lines and uses dedicated CS# lines for the flashes, whereas
Micron shares the CS# and CLK# lines with different IO lines.

Amit, please study the architectures used by mchp, micron and amd and
let us know if they are the same or they differ, and if they differ what
are the differences.

I added Conor from mchp in cc, I see Nicolas is already there, and Bean
from micron.

Thanks,
ta

[1]
https://docs.xilinx.com/r/en-US/am011-versal-acap-trm/QSPI-Flash-Interface-Signals
[2]
https://docs.xilinx.com/viewer/attachment/dwmjhDJGICdJqD4swyVzcQ/fD8nv4ry78xM0_EF5kv4mA
[3]
https://media-www.micron.com/-/media/client/global/documents/products/data-sheet/nor-flash/serial-nor/mt25t/generation-b/mt25t_qljs_l_512_xba_0.pdf?rev=de70b770c5dc4da8b8ead06b57c03500
[4]
https://ww1.microchip.com/downloads/aemDocuments/documents/MPU32/ProductDocuments/DataSheets/SAMA7G5-Series-Data-Sheet-DS60001765.pdf