[U-Boot] [PATCH 5/5] NAND: DaVinci: allow forced disable of subpage writes

[Murali Karicheri]

On 2/18/2014 9:57 AM, Rini, Tom wrote:
> On Wed, Feb 12, 2014 at 06:00:22PM -0600, Scott Wood wrote:
>> On Tue, 2014-01-28 at 23:19 +0000, Karicheri, Muralidharan wrote:
>>>> -----Original Message-----
>>>> From: Scott Wood [mailto:scottwood at freescale.com]
>>>> Sent: Wednesday, January 22, 2014 3:48 PM
>>>> To: Karicheri, Muralidharan
>>>> Cc: u-boot at lists.denx.de; Rini, Tom; Andrianov, Vitaly
>>>> Subject: Re: [U-Boot] [PATCH 5/5] NAND: DaVinci: allow forced disable of subpage writes
>>>>
>>>> On Mon, 2014-01-20 at 17:10 -0500, Murali Karicheri wrote:
>>>>> This patch introduces a configurable mechanism to disable subpage
>>>>> writes in the DaVinci NAND driver.
>>>>>
>>>>> Signed-off-by: Vitaly Andrianov <vitalya at ti.com>
>>>>> Signed-off-by: Murali Karicheri <m-karicheri2 at ti.com>
>>>>> ---
>>>>>   drivers/mtd/nand/davinci_nand.c |    3 +++
>>>>>   1 file changed, 3 insertions(+)
>>>>>
>>>>> diff --git a/drivers/mtd/nand/davinci_nand.c
>>>>> b/drivers/mtd/nand/davinci_nand.c index 5b17d7b..75b03a7 100644
>>>>> --- a/drivers/mtd/nand/davinci_nand.c
>>>>> +++ b/drivers/mtd/nand/davinci_nand.c
>>>>> @@ -609,6 +609,9 @@ void davinci_nand_init(struct nand_chip *nand)
>>>>> #ifdef CONFIG_SYS_NAND_USE_FLASH_BBT
>>>>>   	nand->bbt_options	  |= NAND_BBT_USE_FLASH;
>>>>>   #endif
>>>>> +#ifdef CONFIG_SYS_NAND_NO_SUBPAGE_WRITE
>>>>> +	nand->options	  |= NAND_NO_SUBPAGE_WRITE;
>>>>> +#endif
>>>>>   #ifdef CONFIG_SYS_NAND_HW_ECC
>>>>>   	nand->ecc.mode = NAND_ECC_HW;
>>>>>   	nand->ecc.size = 512;
>>>> Why does it need to be configurable?
>>>>
>>> Same driver used in multiple platforms, and on some platforms like the one
>>> I work with doesn't support subpage writes and has to be disabled.
>> The option needs to be documented, and it should be either named in a
>> davinci-specific manner, or the documentation should clearly list which
>> drivers pay attention to it.
> Agreed.
>
>> It seems odd though, that the ability to support subpage writes is an
>> independent thing rather than a consequence of some other variable such
>> as controller version.
> I suspect this is similar to the OMAP driver where we could support
> subpages but it gets tricky coordinating with the HW ECC engine for BCH8
> and higher.  Perhaps there are davinci targets with smaller ECC levels
> where it works out OK but keystone is doing BCH8 or 16 and it's not
> worth the savings.
Tom/Scott,

My next version of the series will have readme updated with this option 
(no change in name
as this can be used by other drivers as well)  and mention that 
davinci_nand driver is the
driver that currently uses this option.

Murali