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

[Mahapatra, Amit Kumar]

Hello Tudor,

> -----Original Message-----
> From: Tudor Ambarus <tudor.ambarus at linaro.org>
> Sent: Friday, February 9, 2024 4:36 PM
> To: Mahapatra, Amit Kumar <amit.kumar-mahapatra at amd.com>;
> broonie at kernel.org; pratyush at kernel.org; miquel.raynal at bootlin.com;
> richard at nod.at; vigneshr at ti.com; sbinding at opensource.cirrus.com;
> lee at kernel.org; james.schulman at cirrus.com; david.rhodes at cirrus.com;
> rf at opensource.cirrus.com; perex at perex.cz; tiwai at suse.com
> Cc: linux-spi at vger.kernel.org; linux-kernel at vger.kernel.org;
> michael at walle.cc; linux-mtd at lists.infradead.org;
> nicolas.ferre at microchip.com; alexandre.belloni at bootlin.com;
> claudiu.beznea at tuxon.dev; Simek, Michal <michal.simek at amd.com>; linux-
> arm-kernel at lists.infradead.org; alsa-devel at alsa-project.org;
> patches at opensource.cirrus.com; linux-sound at vger.kernel.org; git (AMD-
> Xilinx) <git at amd.com>; amitrkcian2002 at gmail.com; Conor Dooley
> <conor.dooley at microchip.com>; beanhuo at micron.com
> Subject: Re: [PATCH v11 07/10] mtd: spi-nor: Add stacked memories support
> in spi-nor
> 
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> 
> 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".

That's accurate. It's the same concept.
> 
> 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].

That’s correct.
> 
> 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?

Correct.
> 
> 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?

https://docs.xilinx.com/r/en-US/am011-versal-acap-trm/Word-Format
In parallel mode, the driver sets both the CS_LOWER and CS_UPPER bits 
in the Cmd_FIFO_Data register(please refer the above link), and sets 
BUS_SEL to 2’b11 to utilize all 8 IO lines. The controller then manages 
the assertion and de-assertion of the CS# lines.
> 
> 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.

Yes, that's accurate, but the key distinction is that in Microchip, the 
QSPI controller has one CS# (referred to as QCS), whereas the AMD QSPI 
controller has 2 CS#(referred to as CS0 & CS1).

Regards,
Amit

> 
> 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/fD8nv
> 4ry78xM0_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