Date: Fri, 9 Feb 2024 16:13:52 +0000
From: Tudor Ambarus <tudor.ambarus@...aro.org>
To: "Mahapatra, Amit Kumar" <amit.kumar-mahapatra@....com>,
 "broonie@...nel.org" <broonie@...nel.org>,
 "pratyush@...nel.org" <pratyush@...nel.org>,
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Cc: "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
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 Conor Dooley <conor.dooley@...rochip.com>, beanhuo@...ron.com
Subject: Re: [PATCH v11 07/10] mtd: spi-nor: Add stacked memories support in
 spi-nor



On 2/9/24 11:06, Tudor Ambarus wrote:
> 
> 
> 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."

Amit,

I forgot to say my first conclusion about the quote from above. Even if
the dies are in the same physical package, micron asks users to
configure each die as it is a self-standing entity, IOW to configure
each die as it is a flash on its own. To me it looks like 2 concatenated
flashes at first look. Thus identical to how AMD controller works.
Please clarify this.

> 
> 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."

and this would be a parallel concatenation of two flashes.

Then it would be good if you let us now the similarities and differences
between how amd and mchp controller work, I scrawled few ideas below.

thanks,
ta
> 
> 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

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