[U-Boot] [linux-sunxi] [PATCH v2 7/7] spl: nand: sunxi: add support for NAND config auto-detection

[Maxime Ripard <maxime.ripard@free-electrons.com>]

Hi,

On Wed, Jun 01, 2016 at 03:35:07PM +0300, Siarhei Siamashka wrote:
> On Wed,  1 Jun 2016 13:23:24 +0200
> Boris Brezillon <boris.brezillon@free-electrons.com> wrote:
> 
> > NAND chips are supposed to expose their capabilities through advanced
> > mechanisms like READID, ONFI or JEDEC parameter tables. While those
> > methods are appropriate for the bootloader itself, it's way to
> > complicated and takes too much space to fit in the SPL.
> > 
> > Replace those mechanisms by a dumb 'trial and error' mechanism.
> > 
> > With this new approach we can get rid of the fixed config list that was
> > used in the sunxi NAND SPL driver.
> > 
> > Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
> > Acked-by: Hans de Goede <hdegoede@redhat.com>
> 
> We can also have these NAND parameters stored in the SPL header and
> added there by a NAND image builder tool. This may save some precious
> space in the SPL and also improve the reliability of detection.

So you want to favour a solution that hardcodes the NAND configuration
over a solution that runtime-detects what it needs?

I think we are aiming for two very different use-cases: we want to
have everything working ahead of time on various NAND chips during
production, you want to have the end-users being able to reflash
something after the production.

Boris' solution address both use-cases, yours address only the latter.

> Yes, this brings the necessity of the image builder tool into the
> spotlight (something that converts the "u-boot-sunxi-with-spl.bin"
> to a NAND image) but this has always been a problem.

I know you like it a lot, but I don't see how
u-boot-sunxi-with-spl.bin is relevant here. It's an image that has
always been built for the MMC.

We are talking about the NAND here, that will use a different image
format anyway to deal with the randomizer and the ECC, that will have
to use redundancy for the SPL, U-Boot and probably environment images,
that will have to be padded with random data, and doesn't want to
waste the useless (on NAND) padding that is used in that image.

> We have some
> ongoing discussion about this in the linux-sunxi mailing list:
>     https://groups.google.com/forum/#!topic/linux-sunxi/HsWRG-nuV-w
> 
> It also makes a lot of sense to have the NAND support functionality
> enabled in the SPL for all sunxi boards by default

On all the sunxi boards that have NAND at least.

> so the code size does matter. We still do have the runtime
> decompression opportunity as the strategic reserve [1], which should
> provide additional 4 or 5 KiB of space for the code. Still we need
> to be very careful about using up this reserve, to ensure that it is
> well spent on something useful (such as NAND support) instead of
> being just wasted by the bloatware cultists :-)

Good thing we are talking about NAND support and not some bloat then :)

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com
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