On Fri, 2013-09-27 at 04:18 +0000, Gupta, Pekon wrote:
From: Scott Wood [mailto:scottwood@freescale.com]
On Thu, 2013-09-26 at 13:14 +0000, Gupta, Pekon wrote:
From: Gupta, Pekon pekon@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.
Not all NAND controllers expose a low-level interface that matches hwctl() (e.g. fsl_ifc and fsl_elbc). For those that do, we do have a common nand_spl_simple.c that works for many drivers, without needing to hardcode the bus width (though perhaps a few bytes could be shaved off by hardcoding it).
BTW, referring to "driver" in NAND context is ambiguous... I prefer to use it to refer to the controller drivers when not qualified as "high level driver" or similar.
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.
The changelog that introduced am335x_spl_bch.c says that "custom read_page implementation is required for proper syndrome generation." Other than that ECC mode, AFAICT you're already using nand_spl_simple.c.
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.
Unlikely, given that they've all managed to work without this so far. E.g. eLBC and IFC hardcode this information on a per-chip basis in the #defines that hold values for config registers, and prior to this patch omap_gpmc had code to read a config register (regardless of where it originally got set).
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.
It looks like you do more NAND config in gpmc_init() than just setting this one bit, so I don't think you save anything here.
BTW, do you not need to set this bit in the config register for the hardware to work in the SPL case?
-Scott