On Thu, Jun 28, 2012 at 10:46:58AM -0600, Stephen Warren wrote:

On 06/28/2012 12:18 AM, Hiroshi Doyu wrote:

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On Wed, 27 Jun 2012 16:44:14 +0200
Thierry Reding [off-list ref] wrote:

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I think that "coherent_pool" can be used only when the amount of
contiguous memory is short in your system. Otherwise even unnecessary.

Could you explain a bit more why you want carveout size on per-board basis?

In the ideal case I would want to not have a carveout size at all.
However there may be situations where you need to make sure some driver
can allocate a given amount of memory. Having to specify this using a
kernel command-line parameter is cumbersome because it may require
changes to the bootloader or whatever. So if you know that a particular
board always needs 128 MiB of carveout, then it makes sense to specify
it on a per-board basis.

Hm...I could understand somewhat;) but DT can also specify "bootargs"
in dts file, which can support per-board-wide spec too, like the above
sum of carveout needed from all drivers. I just want to avoid
introducing a new parameter additionaly if we can make use of the
existing mechanism.

The bootargs in the DT file is usually provided by (over-written by) the
bootloader. If we start requiring lots of random kernel command-line
arguments, that makes it more effort for the user of the bootloader
(e.g. distribution bootloader scripts, etc.) to create the kernel
command-line. I'd prefer to avoid that as much as possible. That said,
using a standardized command-line option that is (or will be) used by
all (ARM?) SoCs for the same purpose is reasonable, because there's
commonality there.

I propose we stick with the default CMA settings for now and see where
we end up. No need to jump the gun.

Thierry