Hi Grant,
On 19.03.2014 18:03, Grant Grundler wrote:
On Wed, Mar 19, 2014 at 6:12 AM, Tomasz Figa <t.figa@xxxxxxxxxxx> wrote:
...
No. Proper Linux drivers must support deferred probing mechanism and there
should be no assumptions about probing orders. Using other initcall level
than module_initcall for particular drivers is strongly discouraged.
That's true for "end-point" devices. It's not true for
"infrastructure": Memory, CPU, DMA, Interrupt handling, etc. Those
need to be in place before "normal" drivers get called. This SysMMU
driver provides DMA services for "normal" device drivers. Or do I see
that wrong?
Of course using an early initcall level would give you some kind of
guarantees, but it wouldn't guarantee that someone couldn't lower
initcall level for some MMU client driver and break the ordering anyway.
As I said, AFAIK the trend is to get rid of ordering by initcalls and
make sure that drivers can handle missing dependencies properly, even
for "services" such as DMA, GPIO, clocks and so on, which after all are
provided by normal drivers like other.
thanks,
grant
ps. I've written IOMMU support for four different IOMMUs on three
operating systems (See drivers/parisc for two linux examples). But I
still feel like I at best have 80% understanding of how this one is
organized/works. Abstract descriptions and convoluted code have been
handicapping me (and lack of time to dig further).
Well, this is one of my concerns with this driver. It isn't easy to read
(and so review, maintain, extend and debug found issues).
Best regards,
Tomasz
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