On 09/18/2014 10:46 AM, Ezequiel Garcia wrote: > On 18 September 2014 06:59, Brian Norris <computersforpeace@xxxxxxxxx> wrote: >> On Thu, Sep 11, 2014 at 12:02:08PM -0300, Ezequiel Garcia wrote: >>> This commit adds a new platform-data boolean property that enables use >>> of a flash-based bad block table. This can also be enabled by setting >>> the 'nand-on-flash-bbt' devicetree property. >>> >>> If the flash BBT is not enabled, the driver falls back to use OOB >>> bad block markers only, as before. If the flash BBT is enabled the >>> kernel will keep track of bad blocks using a BBT, in addition to >>> the OOB markers. >>> >>> As explained by Brian Norris the reasons for using a BBT are: >>> >>> "" >>> The primary reason would be that NAND datasheets specify it these days. >>> A better argument is that nobody guarantees that you can write a >>> bad block marker to a worn out block; you may just get program failures. >>> >>> This has been acknowledged by several developers over the last several >>> years. >>> >>> Additionally, you get a boot-time performance improvement if you only >>> have to read a few pages, instead of a page or two from every block on >>> the flash. >>> "" >>> >>> Signed-off-by: Ezequiel Garcia <ezequiel@xxxxxxxxxxxxxxxxxxxx> >> >> Pushed this one to l2-mtd.git. Thanks! >> >> But I do have one question below, and I have comments for patch 2. >> >>> --- >>> arch/arm/mach-omap2/gpmc.c | 2 ++ >>> drivers/mtd/nand/omap2.c | 6 +++++- >>> include/linux/platform_data/mtd-nand-omap2.h | 1 + >>> 3 files changed, 8 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/arm/mach-omap2/gpmc.c b/arch/arm/mach-omap2/gpmc.c >>> index 2f97228..b55a225 100644 >>> --- a/arch/arm/mach-omap2/gpmc.c >>> +++ b/arch/arm/mach-omap2/gpmc.c >>> @@ -1440,6 +1440,8 @@ static int gpmc_probe_nand_child(struct platform_device *pdev, >>> break; >>> } >>> >>> + gpmc_nand_data->flash_bbt = of_get_nand_on_flash_bbt(child); >>> + >>> val = of_get_nand_bus_width(child); >>> if (val == 16) >>> gpmc_nand_data->devsize = NAND_BUSWIDTH_16; >>> diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c >>> index 5967b38..e1a9b31 100644 >>> --- a/drivers/mtd/nand/omap2.c >>> +++ b/drivers/mtd/nand/omap2.c >>> @@ -1663,7 +1663,6 @@ static int omap_nand_probe(struct platform_device *pdev) >>> mtd->owner = THIS_MODULE; >>> nand_chip = &info->nand; >>> nand_chip->ecc.priv = NULL; >>> - nand_chip->options |= NAND_SKIP_BBTSCAN; >>> >>> res = platform_get_resource(pdev, IORESOURCE_MEM, 0); >>> nand_chip->IO_ADDR_R = devm_ioremap_resource(&pdev->dev, res); >>> @@ -1692,6 +1691,11 @@ static int omap_nand_probe(struct platform_device *pdev) >>> nand_chip->chip_delay = 50; >>> } >>> >>> + if (pdata->flash_bbt) >>> + nand_chip->bbt_options |= NAND_BBT_USE_FLASH | NAND_BBT_NO_OOB; >>> + else >>> + nand_chip->options |= NAND_SKIP_BBTSCAN; >> >> Can you remind me: why do you use SKIP_BBTSCAN? Doesn't that mean you're >> skipping all boot-time scanning for bad blocks, and resorting to >> on-demand scanning (chip->block_bad()) every time you need to check for >> bad blocks? >> > > Honestly, I have *no* idea, I just retained the previous flag, so to > keep the exact same behavior. > > Roger, any ideas? If I have to guess, I'd say this is an attempt to > save some boot time. > The SKIP_BBTSCAN has been there ever since this driver was introduced in 2009. by commit 67ce04bf2746. I'm not sure why it is preferred. cheers, -roger -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
