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

[Mahapatra, Amit Kumar]

> -----Original Message-----
> From: Tudor Ambarus <tudor.ambarus at linaro.org>
> Sent: Friday, February 9, 2024 9:44 PM
> To: Mahapatra, Amit Kumar <amit.kumar-mahapatra at amd.com>;
> broonie at kernel.org; pratyush at kernel.org; miquel.raynal at bootlin.com;
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> 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;
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> 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
> 
> 
> 
> 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."
> 

Hello Tudor,

> 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.

That’s correct, the Micron flash that you referred can communicate with 
the AMD QSPI controller in both parallel and stacked mode.
> 
> >
> > 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.

That's correct.

Regards,
Amit
> 
> 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-Inter
> > face-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_xb
> > a_0.pdf?rev=de70b770c5dc4da8b8ead06b57c03500
> > [4]
> >
> https://ww1.microchip.com/downloads/aemDocuments/documents/MPU32/
> Produ
> > ctDocuments/DataSheets/SAMA7G5-Series-Data-Sheet-DS60001765.pdf