Mike Rapoport wrote:

Mitch Bradley wrote:

quoted

Mike Rapoport wrote:

quoted

Mitch Bradley wrote:

quoted

The second topic is the hypothetical use of OFW as a HAL. That will 
not happen for several reasons.  The opposition to the idea is 
widespread and deeply held, and there are good arguments to support 
that opposition.   Furthermore, the economic conditions necessary 
for the creation of such a HAL do not exist in the ARM world, nor 
indeed in the Linux world in general.  (The necessary condition is 
the ability for one company to impose a substantial change by fiat 
- essentially a monopoly position.)

Shall we agree, then, that any further discussion of the HAL issue 
is "just for fun", and that nobody needs to feel threatened that it 
would actually happen?

I've recently worked with vendor versions of U-Boot for advanced ARM 
SoCs. There is already *huge* chunk of HAL code in those versions. 
And if there would be possibility to have callbacks into the 
firmware these chunks would only grow, IMHO.

How can there be HAL code in U-Boot unless there is already the 
possibility to have callbacks into the firmware?

Currently it aims to abstract hardware from U-Boot and reuse the same 
HW access code across operating systems and bootloaders. If this code 
would have callbacks I afraid the things would became worse.

The only way I can understand what you said is if I assume that by 
"callback", you mean the following sequence:

a) U-boot loads and executes the OS, providing to the OS the address of 
some HW access routines that it can use
b) The OS calls one of those HW access routines
c) During the execution of that HW access routine, that routine calls 
"back" into the OS, before returning.  So a call into the OS is nested 
inside a call into U-boot resident code.

If that is what you are worried about, it is not what we were 
discussing.  We were discussing - and many people were against - step (b).

Are you saying that step (b) - the OS calling into routines provided by 
U-Boot - is already the status quo?

quoted

It is not HAL if it can't be called.

quoted

quoted

The potential for "vendors breaking out of the debugging use case 
and turning it into a HAL" is miniscule, because

a) The callback is disabled by default
b) The technical challenges of the callback interface limit its 
applicability to specific "wizard user" scenarios
c) OFW is unlikely to achieve sufficient market penetration for the 
HAL thing to be worth doing


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