RE: [[LINUX PATCH v10] 3/4] Documentation: nand: pl353: Add documentation for controller and driver

[Naga Sureshkumar Relli]

Hi Boris,

> -----Original Message-----
> From: Boris Brezillon [mailto:boris.brezillon@xxxxxxxxxxx]
> Sent: Monday, June 25, 2018 2:24 AM
> To: Naga Sureshkumar Relli <nagasure@xxxxxxxxxx>
> Cc: richard@xxxxxx; dwmw2@xxxxxxxxxxxxx; computersforpeace@xxxxxxxxx;
> marek.vasut@xxxxxxxxx; f.fainelli@xxxxxxxxx; mmayer@xxxxxxxxxxxx; rogerq@xxxxxx;
> ladis@xxxxxxxxxxxxxx; ada@xxxxxxxxxxx; honghui.zhang@xxxxxxxxxxxx;
> miquel.raynal@xxxxxxxxxxx; nagasureshkumarrelli@xxxxxxxxx; Michal Simek
> <michals@xxxxxxxxxx>; linux-mtd@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [[LINUX PATCH v10] 3/4] Documentation: nand: pl353: Add documentation
> for controller and driver
> 
> On Thu, 21 Jun 2018 12:12:30 +0530
> Naga Sureshkumar Relli <naga.sureshkumar.relli@xxxxxxxxxx> wrote:
> 
> > Added notes about the controller and driver.
> >
> > Signed-off-by: Naga Sureshkumar Relli <naga.sureshkumar.relli@xxxxxxxxxx>
> > ---
> > Changes in v10:
> >  - None
> > Changes in v9:
> >  - Addressed the comments given by Miquel and Randy
> > Changes in v8
> >  - None
> > Changes in v7:
> > - None
> > Changes in v6:
> > - None
> > Changes in v5:
> > - Fixed the review comments
> > Changes in v4:
> > - None
> > ---
> >  Documentation/mtd/nand/pl353-nand.txt | 99
> +++++++++++++++++++++++++++++++++++
> >  1 file changed, 99 insertions(+)
> >  create mode 100644 Documentation/mtd/nand/pl353-nand.txt
> 
> Can we put these information directly in the driver instead of having
> yet another place where we have things partially documented? I just
> discovered a doc for the pxa NAND controller in this directory because
> of this patch, which kind of proves my point :-).
Ok, but could you please explain where to put in driver?
Do you mean, as comments inside drivers/mtd/raw/pl353-nand.c?

> 
> >
> > diff --git a/Documentation/mtd/nand/pl353-nand.txt b/Documentation/mtd/nand/pl353-
> nand.txt
> > new file mode 100644
> > index 0000000..c352c87
> > --- /dev/null
> > +++ b/Documentation/mtd/nand/pl353-nand.txt
> > @@ -0,0 +1,99 @@
> > +This document provides some notes about the ARM pl353 SMC controller used in
> > +Zynq SOC and confined to NAND specific details.
> > +
> > +Overview of the controller
> > +==========================
> > +	The SMC (PL353) supports two memory interfaces:
> > +	Interface 0 type SRAM.
> > +	Interface 1 type NAND.
> > +	This configuration supports the following configurable options:
> > +	   . 32-bit or 64-bit AXI data width
> > +	   . 8-bit, 16-bit, or 32-bit memory data width for interface 0
> > +	   . 8-bit, or 16-bit memory data width for interface 1
> > +	   . 1-4 chip selects on each interface
> > +	   . SLC ECC block for interface 1
> > +
> > +For more information, refer the below link for TRM
> >
> +http://infocenter.arm.com/help/topic/com.arm.doc.ddi0380g/DDI0380G_smc_pl350_series
> _r2p1_trm.pdf
> > +
> > +NAND memory accesses
> > +====================
> > +	. Two phase NAND accesses
> > +	. NAND command phase transfers
> > +	. NAND data phase transfers
> > +
> > +Two phase NAND accesses
> > +	The SMC defines two phases of commands when transferring data to or from
> > +NAND flash.
> > +
> > +Command phase
> > +	Commands and optional address information are written to the NAND flash.
> > +The command and address can be associated with either a data phase operation to
> > +write to or read from the array, or a status/ID register transfer.
> > +
> > +Data phase
> > + Data is either written to or read from the NAND flash. This data can be either
> > +data transferred to or from the array, or status/ID register information.
> > +
> > +NAND AXI address setup
> > +       AXI address      Command phase      Data phase
> > +	[31:24]         Chip address       Chip address
> > +	[23]            NoOfAddCycles_2    Reserved
> > +	[22]            NoOfAddCycles_1    Reserved
> > +	[21]            NoOfAddCycles_0    ClearCS
> > +	[20]            End command valid  End command valid
> > +	[19]            0                  1
> > +	[18:11]         End command        End command
> > +	[10:3]          Start command      [10] ECC Last
> > +					   [9:3] Reserved
> > +	[2:0]           Reserved           Reserved
> > +
> > +ECC
> > +===
> > +    It operates on a number of 512 byte blocks of NAND memory and can be
> > +programmed to store the ECC codes after the data in memory. For writes,
> > +the ECC is written to the spare area of the page. For reads, the result of
> > +a block ECC check are made available to the device driver.
> > +
> > +------------------------------------------------------------------------
> > +|               n * 512 blocks                  | extra  | ecc    |     |
> > +|                                               | block  | codes  |     |
> > +------------------------------------------------------------------------
> > +
> > +The ECC calculation uses a simple Hamming code, using 1-bit correction 2-bit
> > +detection. It starts when a valid read or write command with a 512 byte aligned
> > +address is detected on the memory interface.
> > +
> > +Driver details
> > +==============
> > +	The NAND driver has dependency with the pl353_smc memory controller
> > +driver for initializing the NAND timing parameters, bus width, ECC modes,
> > +control and status information.
> > +
> > +Since the controller expects that the chip select bit would be cleared for the
> > +last data transfer i.e last 4 data bytes, the existing nand page
> > +read/write routines for soft ECC and ECC none modes will not work. So, in order
> > +to make this driver work, it always updates the ECC mode as HW ECC and
> > +implements the page read/write functions for supporting the SW ECC.
> > +i.e. There is a limitation in SMC controller, that we must set ECC LAST on
> > +last data phase access, to tell ECC block not to expect any data further.
> > +Ex:  When number of ECC STEPS are 4, then till 3 we will write to flash
> > +using SMC with HW ECC enabled. And for the last ECC STEP, we will subtract
> > +4bytes from page size, and will initiate a transfer. And the remaining 4 as
> > +one more transfer with ECC_LAST bit set in NAND data phase register to notify
> > +ECC block not to expect any more data. The last block should be align with end
> > +of 512 byte block. Because of this limitation, we are not using core routines.
> > +
> > +HW ECC mode:
> > +	Up to 2K page size is supported and beyond that it returns
> > +-ENOTSUPPORT error. If the flash has on-die ECC controller then the
> > +priority is given to the on-die ECC controller. Also the current
> > +implementation has support for up to 64 bytes of OOB data.
> > +
> > +SW ECC mode:
> > +	It supports all the page sizes. But since, Zynq SOC bootrom uses
> > +HW ECC for the devices that have page <= 2K. so, When the kernel is not
> > +aware of the ECC mode, it uses HW ECC by default.
> > +
> > +For devicetree binding information please refer to the below dt binding file
> > +Documentation/devicetree/bindings/memory-controllers/pl353-smc.txt.

Thanks,
Naga Sureshkumar Relli.