Re: [PATCH 0/3] An alternative to SPI NAND

[Ezequiel Garcia <ezequiel.garcia@imgtec.com>]

On 01/12/2015 12:10 PM, Qi Wang 王起 (qiwang) wrote:
> Hi Ezequiel,
> 
> On 01/08/2015 11:27 AM, Ezequiel Garcia wrote:
>>
>> Hi Qi Wang,
>>
>> On 01/07/2015 11:45 PM, Qi Wang 王起 (qiwang) wrote:
>>> Hi Brian,
>>>
>>> On Thu, Jan 08, 2015 at 9:03:24AM +0000, Brian Norris wrote:
>>>>
>>>> On Thu, Jan 08, 2015 at 12:47:24AM +0000, Peter Pan 潘栋 (peterpandong)
>>>> wrote:
>>>>> Documentation/devicetree/bindings/mtd/spi-nand.txt |   22 +
>>>>> drivers/mtd/Kconfig                                |    2 +
>>>>> drivers/mtd/Makefile                               |    1 +
>>>>> drivers/mtd/spi-nand/Kconfig                       |    7 +
>>>>> drivers/mtd/spi-nand/Makefile                      |    3 +
>>>>> drivers/mtd/spi-nand/spi-nand-base.c               | 2034
>>>> ++++++++++++++++++++
>>>>> drivers/mtd/spi-nand/spi-nand-bbt.c                | 1279 ++++++++++++
>>>>
>>>> I can already tell by the diffstat that I don't like this. We probably
>>>> don't need 3000 new lines of code for this, but we especially don't want
>>>> to duplicate nand_bbt.c. It won't take a lot of work to augment
>>>> nand_bbt.c to make it shareable. (I can whip that patch up if needed.)
>>>
>>> Yes, I agree with you, Nand_bbt.c do can be shared by Parallel NAND and
>>> SPI NAND. Actually, we are working at this now. Will send patches to you
>>> Once we finished it.
>>>
>>
>> Thanks for the quick submission!
>>
>> However, Brian is right, this code duplication is a no go.
>>
>> Perhaps a more valid approach would be to first identify the code that
>> needs to be shared in nand_bbt.c and nand_base.c, and export those
>> symbols (or maybe do the required refactor).
> 
> Yes, I agree Brian's suggestion in another mail. 
> 
> " The BBT code is something we definitely want to share, but it's actually
> not very closely tied to nand_base.c, and it looks pretty easy to adapt
> to any MTD that implements mtd_read_oob()/mtd_write_oob(). We'd just
> need to parameterize a few relevant device details into a new nand_bbt
> struct, rather than using struct nand_chip directly."
> 
> To abstract a new nand_bbt struct instead of nand_chip to make SPI NAND 
> and parallel NAND can share nand_bbt.c file, I already begin to work on 
> this.
> 
> For code shared in nand_base.c, I agree it would be better if we can find
> a good method to share nand_base.c code between spi nand and parallel nand.
> But frankly speaking, I'm not satisfied for the remap command method. This
> method make code difficult to maintain when SPI NAND and Parallel NAND 
> evolve much differently in the future.
> 
> Take some example, 
> If one new command (cache operation, multiple plane operation) implemented 
> in parallel NAND code, and is used in nand_read or nand_write, that will 
> cause maintainer to modify SPI NAND code to remap this new command, though 
> this modification probably could be slight. That means modification on 
> Parallel NAND flash need to consider SPI NAND as well. 
> 
> How do you think about this?
> 
> For Peter Pan's patchset, if we do some modification to make nand_bbt.c to
> make it shareable for Parallel and SPI NAND. The code line should be 2000.
> I believe I can review this spi-nand-base.c to remove some redundant code
> that may hundreds line. Is 1700 or 1800 code line is more acceptable?
> 
> Let me know your opinions.
> 

Sounds good.

Do you still plan to maintain the spi-nand-base.c and spi-nand-device.c
separation?
-- 
Ezequiel