[PATCH v4 0/6] Introducing the Alpine platform.

[arnd@arndb.de (Arnd Bergmann)]

On Thursday 05 February 2015 10:28:02 Ronen Shitrit wrote:
> On 4 February 2015 at 14:33, Arnd Bergmann <arnd@arndb.de> wrote:
> > On Wednesday 04 February 2015 13:19:04 Tsahee Zidenberg wrote:

> > I understand where you are coming from, as this is something that
> > everyone gets wrong at first.
> 
> In order to bring up a completely new silicon with lots of
> technologies challenges in such short time and take it to production,
> with multi discipline environments, few OSs support and small software
> group, we had to share code as much as possible == hal.

I think the most important part for you to understand is not to call
something a hal (or os abstraction, which would be worse), as that
is universally hated. ;-)

> We were aware from first day of the obstacles of merging hal code to
> the mainline, that why we implemented it using linux coding style,
> trying to minimize the "resistance", and we hoped (and still are :) to
> find a path to keep part of our low level code into the mainline.
> If it wont work out, we will rewrite it...

It's not as bad if something is contained within one driver: if you have
e.g. a network driver that consists of a low-level part that talks to
the hardware and a high-level part that talks to linux, that can
be ok. What you should avoid is having interfaces that span across
multiple driver components and use a global header file for the
interface but are specific to one SoC family.

> >However, you will not be able to merge
> > the drivers with a HAL like this. The kernel abstracts all the
> > components of typical SoCs already and I suspect you just did not
> > use the right abstraction because you either didn't find it, or it
> > was not there at the time you started the work.
> >
> > For example, a DMA subsystem that is used by multiple slave drivers
> > should use a driver in drivers/dma that registers to the slave-dma API,
> 
> If you are referring to the dma-engine api, than this is a good
> example where we don't want to use the generic framework as its
> overhead on performance is unacceptable.

It also illustrates my point: When we introduce a second interface
in parallel to the existing one, this puts a burden on us upstream
maintainers which now have to understand and maintain both. We used
to have all sorts of interfaces per SoC and are almost done consolidating
them to all use dmaengine for this reason.
I do realize that the dmaengine API is not perfect though, so if you
have specific problems with it, we expect you to help figure out what
they are and what we can do about them so that everybody benefits.

To a certain extent, this is how we make progress in the kernel with
generic interfaces: someone has a particular need and it's up to them
to implement the groundwork. In return they get all the features of
the kernel that someone else needed and implemented already.

	Arnd