[U-Boot] [PATCH 1/1] am33xx: add CONFIG_SYS_NAND_DEVICE_WIDTH to determine NAND device bus-width

[Gupta, Pekon]

> From: Scott Wood [mailto:scottwood at freescale.com]
> 
> On Thu, 2013-09-26 at 13:14 +0000, Gupta, Pekon wrote:
> > > > From: Gupta, Pekon <pekon at ti.com>
> > > >
> > > > NAND driver needs to know bus-width of the connected NAND device,
> in
> > > order to perform proper I/O and initialize itself. Currently there is no
> CONFIG
> > > option to provide this information to NAND driver.
> > > > - SPL NAND driver does not have framework to parse ONFI parameter
> > > page.
> > >
> > > Is this about SPL?  It looks like a more general change.
> > >
> > Yes, actually I would have loved to see a generic SPL driver for all platforms,
> 
> How could that possibly work?
> 
NAND SPL (as in drivers/mtd/nand/am335x_spl_bch.c) had following limitation
(a) depends on CONFIG_SYS_NAND_xx (for NAND device parameters like
	 erasesize, pagesize, oobsize, etc).
(b) can only do NAND read access.
(c) calls nand_chip->ecc.hwctl() for doing controller specific
	 configurations, which is populated while doing board_nand_init().

Above (a), (b), and (c) do not have any SoC specific dependency. And can be
put into a generic framework which can be used for all SPL drivers.

All SoC specific configurations are done in either:
- board_nand_init(): initializations based on device.
- nand_chip->ecc.hwctl(): configurations for ECC scheme.
which is *shared* code between SPL & u-boot driver, and is present in
u-boot driver file (like drivers/mtd/nand/omap_gpmc.c), not in SPL driver file.

The missing piece was device bus-width detection which I addresses in
this patch by adding CONFIG_SYS_NAND_DEVICE_WIDTH.


> > because SPL is mostly statically configured, and it just does plain NAND read
> > (it doesn’t even support NAND write, etc).
> > But I do not know the hardware configurations tweaks of other SoC,
> > So at-least have common CONFIG_SYS_NAND_xx which all SPL drivers can
> use.
> 
> Again, are you introducing this symbol for use only in SPL? 
Apart from SPL, CONFIG_SYS_NAND_DEVICE_WIDTH also be useful for
(1) drivers which do not use CONFIG_SYS_NAND_ONFI_DETECTION, where
     code for reading on-chip ONFI parameters is not enabled in nand_base.c
(2) non ONFI compatible NAND devices.


> It looked
> like you were removing the code that does dynamic detection, which would
> also affect non-SPL.
> 
>  > -	/* If we are 16 bit dev, our gpmc config tells us that */
> >  -	if ((readl(&gpmc_cfg->cs[cs].config1) & 0x3000) == 0x1000)

omap_gpmc.c never had dynamic detection support. Above gpmc_config bit
which is used to tell whether device is x16 or x8, gets actually hard-coded in
gpmc_init(). Thus it was actually a mechanism to pass hard-coded bus-width
information to nand driver.
Refer: arch/arm/cpu/armv7/am33xx/mem.c : gpmc_init()

So, instead of hacking the gpmc_init() everytime for different devices,
this patch introduces a generic CONFIG which can be used everywhere.

I have sent this patch separately to see the acceptance of new generic
CONFIG_SYS_NAND_DEVICE_WIDTH. If this gets accepted, then I'll 
resend the patch-series which actually does dynamic detection..
http://lists.denx.de/pipermail/u-boot/2013-September/162295.html
http://lists.denx.de/pipermail/u-boot/2013-September/162296.html

(dropping others in CC list as u-boot maillist rejects the mail saying
too many recipients. !! )

with regards, pekon